RESEARCH ARTICLE
Is mass drug administration against lymphatic
filariasis required in urban settings? The
experience in Kano, Nigeria
Dung D. Pam1‡, Dziedzom K. de Souza2‡*, Susan D’Souza3, Millicent Opoku2,
Safiya Sanda4, Ibrahim Nazaradden4, Ifeoma N. Anagbogu5, Chukwu Okoronkwo5,
Emmanuel Davies5, Elisabeth Elhassan4, David H. Molyneux6, Moses J. Bockarie7,
Benjamin G. Koudou6,8
1 Applied Entomology and Parasitology Unit, Department of Zoology, University of Jos, Jos, Nigeria,
a1111111111
2 Parasitology Department, Noguchi Memorial Institute for Medical Research, University of Ghana, Legon,
a1111111111
Ghana, 3 Sightsavers International, UK Office, London, United Kingdom, 4 Sightsavers International, Nigeria
a1111111111 Office, Kaduna, Nigeria, 5 NTD Division, Federal Ministry of Health, Abuja, Nigeria, 6 Centre for Neglected
a1111111111 Tropical Diseases and Department of Parasitology, Liverpool School of Tropical Medicine, Liverpool, United
a1111111111 Kingdom, 7 European and Developing Countries Clinical Trials Partnership, Africa Office, Cape Town, South
Africa, 8 UFR Science de la Nature, Université Nangui Abrogoua, Abidjan, Cote d’Ivoire
‡ These authors are joint senior authors on this work.
* DDeSouza@noguchi.ug.edu.gh
OPENACCESS
Citation: Pam DD, de Souza DK, D’Souza S, Opoku Abstract
M, Sanda S, Nazaradden I, et al. (2017) Is mass
drug administration against lymphatic filariasis
required in urban settings? The experience in Kano,
Background
Nigeria. PLoS Negl Trop Dis 11(10): e0006004.
https://doi.org/10.1371/journal.pntd.0006004 The Global Programme to Eliminate Lymphatic Filariasis (GPELF), launched in 2000, has
Editor: Wilma A. Stolk, Erasmus MC, the target of eliminating the disease as a public health problem by the year 2020. The strat-
NETHERLANDS egy adopted is mass drug administration (MDA) to all eligible individuals in endemic commu-
Received: February 8, 2017 nities and the implementation of measures to reduce the morbidity of those suffering from
chronic disease. Success has been recorded in many rural endemic communities in which
Accepted: October 2, 2017
elimination efforts have centered. However, implementation has been challenging in several
Published: October 11, 2017
urban African cities. The large cities of West Africa, exemplified in Nigeria in Kano are chal-
Copyright: © 2017 Pam et al. This is an open lenging for LF elimination program because reaching 65% therapeutic coverage during
access article distributed under the terms of the
MDA is difficult. There is therefore a need to define a strategy which could complement
Creative Commons Attribution License, which
permits unrestricted use, distribution, and MDA. Thus, in Kano State, Nigeria, while LF MDA had reached 33 of the 44 Local Govern-
reproduction in any medium, provided the original ment Areas (LGAs) there remained eleven ‘urban’ LGAs which had not been covered by
author and source are credited.
MDA. Given the challenges of achieving at least 65% coverage during MDA implementation
Data Availability Statement: All relevant data are over several years in order to achieve elimination, it may be challenging to eliminate LF in
within the paper and its Supporting Information
such settings. In order to plan the LF control activities, this study was undertaken to confirm
files.
the LF infection prevalence in the human and mosquito populations in three urban LGAs.
Funding: The study was sponsored by NTD/United
Programmes supported by DFID. DHM was
Methods
supported in part from the COUNTDOWN
partnership (grant ID PO 6407) a multi-disciplinary The prevalence of circulating filarial antigen (CFA) of Wuchereria bancrofti was assessed by
research consortium dedicated to investigating
an immuno-chromatography test (ICT) in 981 people in three urban LGAs of Kano state,
cost-effective, scaled-up and sustainable solutions,
necessary to control and eliminate Neglected Nigeria. Mosquitoes were collected over a period of 4 months from May to August 2015
Tropical Diseases. COUNTDOWN is funded by using exit traps, gravid traps and pyrethrum knock-down spray sheet collections (PSC) in
PLOS Neglected Tropical Diseases | https://doi.org/10.1371/journal.pntd.0006004 October 11, 2017 1 / 15
Evidence against MDA in urban Kano, Nigeria
UKAID, part of the Department for International different households. A proportion of mosquitoes were analyzed for W. bancrofti, using dis-
Development (DFID). The funders had no role in section, loop-mediated isothermal amplification (LAMP) assay and conventional polymer-
study design, data collection and analysis, decision
ase chain reaction (PCR).
to publish, or preparation of the manuscript.
Competing interests: DHM acknowledges support
from GlaxoSmithKline and Sightsavers. The
authors have declared that no competing interests Results
exist. The results showed that none of the 981 subjects (constituted of <21% of children 5–10
years old) tested had detectable levels of CFA in their blood. Entomological results showed
that An. gambiae s.l. had W. bancrofti DNA detectable in pools in Kano; W. bancrofti DNA
was detected in between 0.96% and 6.78% and to a lesser extent in Culex mosquitoes
where DNA was detected at rates of between 0.19% and 0.64%. DNA analysis showed that
An. coluzzii constituted 9.9% of the collected mosquitoes and the remaining 90.1% of the
mosquitoes were Culex mosquitoes.
Conclusion
Despite detection of W. bancrofti DNA within mosquito specimens collected in three Kano
urban LGAs, we were not able to find a subject with detectable level of CFA. Together with
other evidence suggesting that LF transmission in urban areas in West Africa may not be of
significant importance, the Federal Ministry of Health advised that two rounds of MDA be
undertaken in the urban areas of Kano. It is recommended that the prevalence of W. ban-
crofti infection in the human and mosquito populations be re-assessed after a couple of
years.
Author summary
Mass drug administration (MDA) for the control of elephantiasis in the state of Kano in
Nigeria, started in the year 2010. It was estimated that by 2015, the MDA programme will
be extended to 11 remaining urban Local Government Areas (LGAs). However, MDA in
urban areas faces specific challenges, the most prominent being the need to achieve cover-
age rates of 65% and above. As such MDA alone may not be sufficient to achieve the
required programme impacts of reducing LF transmission to levels below which transmis-
sion cannot be sustained, and additional interventions may be required. This study set out
to confirm the LF infection prevalence in the human and mosquito populations in three
urban LGAs in Kano. Individuals were tested for signs of the disease, and mosquito sam-
ples were collected and also tested for the worms that cause the disease. The study revealed
that of 981 people tested, none had circulating filarial antigen in the blood. However, the
mosquitoes collected revealed the presence of the disease-causing worms, but the level of
infection was low. The infection in the mosquitoes was also detected in two different types
of mosquitoes. Based on the outcomes of this study, and evidence from other West Afri-
can cities on the transmission of LF, the Federal Ministry of Health recommended that
two rounds of MDA be undertaken in urban areas of Kano. A further reassessment after a
couple of years is warranted.
PLOS Neglected Tropical Diseases | https://doi.org/10.1371/journal.pntd.0006004 October 11, 2017 2 / 15
Evidence against MDA in urban Kano, Nigeria
Introduction
Lymphatic filariasis (LF) is a disease caused by Nematode worms that live in the lymphatic ves-
sels of humans. There are three species of filarial parasites which infect humans—Wuchereria
bancrofti, Brugia malayi and Brugia timori. In Africa, LF is caused by W. bancrofti and is trans-
mitted by Anopheles mosquitoes in rural settings and Anopheles and culicine mosquitoes in
urban areas [1,2]. LF is a significant health problem in many developing countries with about
1.4 billion people known to live in endemic areas, with one quarter potentially infected [3]. LF
is also the second leading cause of permanent disability and undermines the social and eco-
nomic welfare of affected people and communities [4]. The World Health Assembly passed a
resolution in 1997 to eliminate LF as a public health problem by the year 2020. The World
Health Organization has since 2000 launched a Global Programme to Eliminate Lymphatic
Filariasis (GPELF) [5]. Annual mass treatment with single-dose diethylcarbamazine (DEC) or
ivermectin (IVM) in combination with albendazole (ALB) for 4–6 years is the principal tool of
the elimination strategy. This has resulted in dramatic progress in reducing the prevalence of
LF in many areas around the world through MDA [6].
The problem of urban LF remains a matter of debate, yet it is recognized as being a key
challenge to the ongoing global efforts to eliminate LF as a public health problem [7]. This is,
in part, due to the challenges of translating MDA procedures that were developed for rural
areas to the urban environment, with its distinctive patterns of human organization and
behaviour, and in part due to the proliferation of potential urban vectors in poorly planned
urban settlements [2]. In West Africa where Anopheles mosquitoes are the main vectors of LF
and Culex plays little, if any, role in LF transmission, the status of urban transmission remains
ill- defined as studies of LF transmission in cities in Sierra Leone and Guinea found no evi-
dence of transmission [8,9]. Given the rapid expansion of urban centres in West Africa over
recent decades, driven by population increases, insecurity and rural-urban migration the pol-
icy for treatment of these populations needs to be defined based on the evidence that transmis-
sion is ongoing and is likely to be sustained.
In the State of Kano, Nigeria, LF MDA started in 2010 and as of 2014, had reached 33 of the
44 Local Government Areas (LGAs) known to be LF endemic. Under the plans for 2015 LF
MDA was to be extended to the remaining 11 LGAs including, six ‘urban’ LGAs. In 2010, base-
line ICT prevalence surveys conducted in these six urban LGAs revealed high ICT prevalence
rates between 2 and 22%. Given such high pre-control endemicity levels added to the chal-
lenges of MDA implementation in urban settings, it may be useful to confirm the prevalence
rates before embarking on MDA. The main goal of this study was to verify previous survey
results carried out in Kano urban settings which suggested that LF is endemic. Entomological
surveys were then conducted to determine the intensity of ongoing transmission in large cities
in the light of recent findings that LF transmission is not sustainable in the capitals of Sierra
Leone [8] and Guinea [9] despite the presence of antigen positives.
Materials and methods
Ethics statement
Ethical Clearance (MOH/OFF/797/Ti/15) was given by the Kano State Ministry of Health Eth-
ical Committee. Additionally, all surveys were conducted in accordance with the study proto-
col approved by the Institutional Ethics Review Board of the Liverpool School of Tropical
Medicine (1189RS). All levels of leadership in the three Local Government Areas used for this
study were met and their approval of the work was received. Written informed consent was
obtained from all study participants above the age of 18 years, as well as parental consent from
PLOS Neglected Tropical Diseases | https://doi.org/10.1371/journal.pntd.0006004 October 11, 2017 3 / 15
Evidence against MDA in urban Kano, Nigeria
children below the age of 18 years. The children below 18 years provided oral consent for the
study.
Study area and sites
Selection of study communities was based on a previous mapping by the Federal Ministry of
Health, which indicated that urban LGAs were endemic for LF in Kano State. The mapping sur-
vey was undertaken in 2010, following WHO recommendations [10]. Communities were
selected in LGAs, based on key informant identification of communities most likely to be
endemic for filariasis. Following community sensitization, 50–100 consenting volunteers were
invited to a designated place where they were examined for W. bancrofti antigenemia using the
ICT cards. The results of the mapping survey are presented in Table 1. The current study was
carried out in three of the urban LGAs included in the mapping survey (Ungogo, Fagge and
Nasarawa). The LGAs and study communities were randomly selected among those having the
lowest and the highest antigenemia rates recorded during the mapping survey. However, in
Nasarawa LGA Goji, which was peri-urban, was replaced by Gama (an urban community). Jaba
in Fagge LGA and Dankukuru in Ungogo LGA were also urban communities. In these LGAs
neither LF MDA nor MDA for onchocerciasis based on ivermectin has been previously con-
ducted. Kano State is located in Northern Nigeria, on latitude 110 300 N—110 500 N and longi-
tude 80 300 E—80 500 E. The state is bound by four other states, all of which are endemic for LF-
Katsina State to the North-west, Jigawa State to the North-east, Kaduna State to the South-west
and Bauchi State on the South-eastern border. The status of Kano State as an LF endemic state
has previously been established as a 1.6% prevalence was found in some villages [11].
Circulating filarial antigen (CFA) survey
A serological survey was carried out following the WHO guidelines [12] in May 2015. Individu-
als living in the selected communities were sensitized and informed by community health work-
ers and health officers of the urban LGAs about the survey. The sensitization was done in
churches and mosques and other socio-economic groups. Additionally, a town crier was used
in the selected communities to inform community members about the survey and individuals
5 years willing to take part in the survey were then invited to a designated community location
(schools and urban health center) where finger-prick blood samples were taken. We used the
immune-chromatography card test (ICT) (Alere, NOW, ICT filariasis kits; Binax, Portland,
USA) for the detection of circulating filarial antigen in finger-prick blood samples taken during
the day. All batches of ICT cards used were tested for quality control using serum from LF posi-
tive individuals, provided by the Noguchi Memorial Institute for Medical Research (NMIMR).
All test results were read after 10 minutes according to the manufacturer’s instructions.
Mosquito sampling
Mosquitoes were collected over a 4-month period from May to August 2015, using exit traps,
gravid traps and pyrethrum knock-down spray sheet collections (PSC) in different households.
The use of these various trapping methods was to augment the number of samples collected
and analyzed for the study. The estimated sample size was 1000 vector mosquitoes (100 pools
of 20 mosquitoes per pool per site) required in order to estimate an infection rate of 1% with a
power of 0.80 [13]. Mosquito collections were done in the same communities where the parasi-
tological surveys were undertaken. According to the information provided by the district
health officers of the three urban communities, mosquito collection points were also selected
based on the observation of risk factors such as presence of mosquito breeding sites, increasing
potential exposure of the population to mosquito bites.
PLOS Neglected Tropical Diseases | https://doi.org/10.1371/journal.pntd.0006004 October 11, 2017 4 / 15
Evidence against MDA in urban Kano, Nigeria
Table 1. Results of 2010 mapping survey in Kano state.
IU Locality No. Examined No. Positives ICT Prevalence (%)
Ajingi Ungu War Bai 47 7 14.9
Albasu Faragai 50 1 2.0
Bagwai Rimin Dako 50 5 10.0
Bebeji Ran Tan 45 2 4.4
Bichi YanaIami 45 1 2.2
Bunkure Bunkure 50 1 2.0
Dala DaIa 50 6 12.0
Dambatta Ajumawa 47 2 4.3
Dawakin-Kudu Kogar Kaza 50 5 10.0
Dawakin-Tofa Sarauniya 47 3 6.4
Doguwa Natsohuwa 49 5 10.2
Fagge Jaba 50 2 4.0
Gabasawa Gunduwa 46 6 13.0
Garko Kafinchiri 50 2 4.0
Garun-Malam G/Babba 49 5 10.2
Gaya Gaya North 50 1 2.0
Gezawa Mesa Tudu 50 1 2.0
Gwale Ja’en 50 1 2.0
Gwarzo Koya 48 2 4.2
Kabo Durun 50 5 10.0
Kano Municipal Sharada 50 4 8.0
Karaye Turawa 39 4 10.3
Kibiya Tarai 50 1 2.0
Kiru Bauda 48 1 2.1
Kumbosto Yan-Shana 50 2 4.0
Kunchi Shuwaki 50 5 10.0
Kura DaIiIi Kura 100 2 2.0
Madobi Rikadawa 50 1 2.0
Makoda Makoda city 50 3 6.0
Minjibir Wasai 35 2 5.7
Nasarawa K/Goji 50 11 22.0
Rano Rano S/G 49 5 10.2
Rimin Gado Rimin Gado 50 4 8.0
Rogo Tajaye 42 4 9.5
Shanono Marabutawa 50 4 8.0
Sumaila SumaiIa 49 4 8.2
Takai Faruruwa 50 12 24.0
Tarauni Dantsinke 50 3 6.0
Tofa Gajida 50 6 12.0
Tsanyawa Tsanyawa 50 4 8.0
Tudun-Wada Yar Yaso 50 6 12.0
Ungogo Dankunkuru 50 6 12.0
Warawa Jigawa 50 1 2.0
Wudil Darki 50 2 4.0
https://doi.org/10.1371/journal.pntd.0006004.t001
Firstly, exit (window) traps, targeting host-seeking adults were installed in fifteen different
randomly selected households, five in each LGA. Householders were asked to collect
PLOS Neglected Tropical Diseases | https://doi.org/10.1371/journal.pntd.0006004 October 11, 2017 5 / 15
Evidence against MDA in urban Kano, Nigeria
mosquitoes for 10-days, each morning, during the mosquito collection period—for which they
received a small remuneration. This yielded a total of 600 sampling days (3 LGAs x 5 traps x 10
days x 4 months). Both exit traps and PSC were performed in different households on the
same day. However, when mosquito catches were consistently low in any household, such
households were replaced by others in the neighborhood.
Pyrethrum spray catches (PSC) targeting resting adult mosquitoes were carried out inside
the sleeping room of three randomly selected households (different from those used for the
exit trap) in each site. Each month the collection period lasted for 7 days, therein yielding a
total sampling effort of 252 sampling days (3 LGAs x 4 months x 7 days per month x 3 house-
holds per sampling day). A different set of three houses was sampled on each of the seven sam-
pling days per month. The PSC method consisted of spraying an insecticide (pyrethroid) in
selected rooms. Mosquitoes were collected on a white sheet covering the floor space of the
sleeping room 10 minutes after spraying the rooms.
Gravid trap collections were performed outside five randomly selected collection points in
each LGA. Each month the collection period lasted 7 days therein yielding a total sampling
effort of 420 days (3 LGAs x 4 months x 7 days per month x 5 traps / site). Gravid traps are
highly efficient for sampling Culex species. The trap attracts females with an oviposition attrac-
tant medium contained in a pan below the trap [14]. Previous studies in West African cities
have shown that the mosquito fauna is dominated by Culex species [8,9,15], as a result of the
polluted breeding environments. While Culex is considered as a non-vector species in West
Africa [16], it has been shown that parasite DNA can be identified in both vector and non-vec-
tor species after ingestion of parasite positive blood [17,18]. As such, identifying W. bancrofti
parasite or DNA in any mosquito species is enough to reveal the presence of an infected indi-
vidual. The use of Culex gravid traps was therefore to augment the chances of identifying
infected mosquitoes in the study areas.
Mosquito processing
Each month, during the entomology survey mosquitoes collected by each trapping method
were taken to the nearest suitable field laboratory for further processing. Mosquitoes collected
were identified to the genus and species level using morphological identification keys [19,20].
Following identification, the specimens were placed individually in coded vials and kept dry in
tins containing silica gel for future processing. The mosquitoes were then sent to the NTD Ref-
erence laboratory of the Noguchi Memorial Institute for Medical Research, for molecular iden-
tification and processing for W. bancrofti infection.
Species and molecular forms of Anopheles gambiae complex
For the species identification of the members of the An. gambiae complex, a maximum of 100
mosquitoes were processed from each community. Where the number was less than 100, all
mosquitoes were processed.
Genomic DNA was extracted from the legs of each mosquito, using the boiling preparation
method; the legs were crushed in 100ml of distilled water and boiled at 95˚C for 10 minutes.
The supernatant was subsequently used as template for the PCR. Mosquitoes in the An. gam-
biae complex were then identified to species and molecular forms using the PCR method of
Fanello et al. [21].
Molecular identification of W. bancrofti DNA in mosquitoes
Mosquitoes were pooled according to community, trapping method and abdominal status.
The pool range was 1–20. DNA was extracted from each pool using the Qiagen DNEasy tissue
PLOS Neglected Tropical Diseases | https://doi.org/10.1371/journal.pntd.0006004 October 11, 2017 6 / 15
Evidence against MDA in urban Kano, Nigeria
kit. The identification of W. bancrofti DNA was performed using the LAMP method [22] and
the conventional PCR method [23], for confirmation. The LAMP method uses four primers
that are simultaneously used to initiate DNA synthesis from the original unamplified DNA to
generate a stem-loop DNA for subsequent LAMP cycling, and is thus faster, more sensitive
and less susceptible to inhibition, compared to the conventional PCR method. We did not
assess the infectivity rate of W. bancrofti stage specific L3 parasites. Only the presence of W.
bancrofti DNA in mosquitoes was assessed, hence we cannot conclude on the status of
transmission.
Quality control
All assays included a known positive control (DNA extracted from a mosquito pool seeded
with W. bancrofti microfilariae), and a negative control. All W. bancrofti positive pools were
confirmed, by repeating the assay a second time. If a positive pool turn negative after repeat,
the sample is re-run a third time for confirmation. If it is still negative, it is considered
negative.
Statistical analysis
The numbers of Anopheles and Culex mosquitoes were collated and calculated as percentages
of the totals for site trapping method and month of collection. The pool screening software
(Version 2.0) was used to estimate the maximum likelihood estimates (MLE) of the prevalence
of W. bancrofti infection in the mosquitoes [24,25].
Results
During this survey, 305, 304 and 372 individuals were examined for circulating filarial antigen
(CFA) from Fagge, Ungogo and Nasarawa, respectively, giving a total of 981 individuals
(Table 2). None of the subjects had detectable circulating W. bancrofti parasite antigen.
A total of 19,690 mosquitoes consisting of 2,600 An. gambiae, 17,082 Culex mosquitoes and
8 mosquitoes belonging to other species were collected (Table 3). The number of Anopheles
mosquitoes collected was low in the dry season months of May, June and July, but peaked at
the beginning of the rainy season in August.
A proportion of the mosquitoes were dissected to determine infection with W. bancrofti. In
all, 8,809 mosquitoes were dissected- 1324 An. gambiae and 7,485 Culex mosquitoes. All mos-
quitoes dissected to examine for larvae of W. bancrofti were negative suggesting that transmis-
sion was not taking place. Molecular identification of W. bancrofti identification revealed the
presence of DNA in both An. gambiae and Culex mosquitoes. 602 pools of mosquitoes (pool
ranges of 1–20) were analyzed out of which 62 pools were positive for W. bancrofti DNA.
Overall, higher prevalences were observed in Anopheles compared to Culex (Table 4). The
prevalence of W. bancrofti DNA in Fagge was 0.69% in the An. gambiae and 0.64% in Culex
spp. In Nasarawa, the prevalence of DNA in samples was 6.78% and 0.48% in An. gambiae and
Culex, respectively, while in Ungogo it was 4.55% and 0.19% in An. gambiae and Culex, respec-
tively. The data was also analyzed based on the trapping method used (Table 5). It can be
observed that the use of the PSC and the gravid traps resulted in higher infection rates, com-
pared to the used of the exit traps.
Molecular analysis of samples of the An. gambiae s.l. showed that most members of the spe-
cies complex in the three study communities were An. coluzzii, previously known as the M
form of An. gambiae s.s. Only one An. gambiae s.s. and one An. arabiensis were identified
(Table 6).
PLOS Neglected Tropical Diseases | https://doi.org/10.1371/journal.pntd.0006004 October 11, 2017 7 / 15
Evidence against MDA in urban Kano, Nigeria
Table 2. ICT results for three urban LGAs of Kano state.
L.G.A(Community) Sex No. Tested Age Group (years) No. (%) +ve
<11 11–20 21–30 31–40 >41
Fagge (Jaba) Females 167 41 45 34 23 24 0 (0.0)
Males 138 32 51 27 11 17 0 (0.0)
Nasarawa (Gama) Females 158 17 19 15 15 92 0 (0.0)
Males 214 27 58 19 12 98 0 (0.0)
Ungogo (Dankunkuru) Females 126 35 39 25 14 13 0 (0.0)
Males 178 54 53 25 23 23 0 (0.0)
Total Females 451 93 103 74 52 129 0 (0.0)
Males 530 113 162 71 46 138 0 (0.0)
https://doi.org/10.1371/journal.pntd.0006004.t002
Discussion
A cross-sectional ICT antigen detection survey carried out in May 2015 in the three urban
LGAs of Kano state revealed that none of the 981 individuals aged5 years had detectable lev-
els of CFA. This contradicts the mapping results undertaken by the NTD program from the
Federal Ministry of Health in the study area in 2010 (5 years earlier) which reported prevalence
of circulating filarial antigen varying between 2% and 12% in these LGAs. It will be important
to know what factors have led to the reduction in LF prevalence from the mapping records or
if the ICT tests available were recording false positives. It is known that vector control inter-
ventions have the potential to impact LF elimination activities [26,27] and the level of vector
control interventions implemented between previous mapping and the current study could
provide further evidence for LF elimination using vector control in Africa. In Kano state free
distribution of insecticide treated nets was reported, which showed ITN ownership increasing
more than 10-fold, from 6% to 71% [28]. It is further possible that the insecurity in northern
Nigeria could have contributed significantly to the increase in the number of people migrating
from rural areas to cities such as Kano. 3.3 million persons were displaced due of Boko Haram
attacks from Borno, Yobe and Adamawa States to Kano in the last 5 years [29]. As a result it
may be possible that the LF prevalence in urban Kano in 2010 may be a result of rural to urban
migration of antigen positive individuals that are likely to have acquired the infection
elsewhere.
Table 3. Monthly collections of mosquito species in the three urban L.G.A.s of Kano.
Month Species L.G.A. (Community) Total
Fagge (Jaba) Nasarawa (Gama) Ungogo (Dankunkuru)
May An. gambiae 2 0 21 25
Cx. quinquefascitus 1257 2613 2312 6182
Other species 0 0 1 1
June An. gambiae 4 0 7 11
Cx. quinquefascitus 435 628 144 1207
Other species 0 0 2 2
July An. gambiae 22 0 9 31
Cx. quinquefascitus 684 820 101 1605
Other species 0 0 0 0
August An. gambiae 1304 76 1153 2533
Cx. quinquefascitus 4545 1266 2277 8088
Other species 2 1 2 5
https://doi.org/10.1371/journal.pntd.0006004.t003
PLOS Neglected Tropical Diseases | https://doi.org/10.1371/journal.pntd.0006004 October 11, 2017 8 / 15
Evidence against MDA in urban Kano, Nigeria
Table 4. W. bancrofti infection rates in pools of Anopheles and Culex mosquitoes by PCR examined from the study sites.
LGA Species Abdominal Condition No. of mosquitoes Pools examined Pools positive MLE (%) 95% CI
Fagge An. gambiae Unfed 311 17 1 0.33 0.01, 1.67
Fed 192 14 2 1.04 0.12, 3.61
Gravid 83 5 1 1.24 0.04, 6.24
Total 586 36 4 0.69 0.18, 1.77
Culex spp. Unfed 730 42 2 0.28 0.03, 0.97
Fed 265 19 3 1.21 0.23, 3.46
Gravid 2636 141 17 0.69 0.38, 1.13
Total 3631 202 22 0.64 0.38, 0.99
Nasarawa An. gambiae Unfed 20 2 0 - -
Fed 14 2 1 18.37 0.49, 93.84
Gravid 3 2 1 42.27 1.60, 96.87
Total 37 6 2 6.78 0.81, 22.66
Culex spp. Unfed 1396 73 8 0.61 0.24, 1.22
Fed 365 24 2 0.57 0.07, 1.97
Gravid 1463 81 5 0.35 0.11, 0.83
Total 3224 178 15 0.48 0.26, 0.82
Ungogo An. gambiae Unfed 302 18 9 3.96 1.69, 7.68
Fed 84 8 3 4.86 0.94, 14.11
Gravid 38 4 2 12.55 1.32, 55.99
Total 424 30 14 4.55 2.34, 7.85
Culex. spp Unfed 1472 78 3 0.21 0.04, 0.60
Fed 497 32 0 - -
Gravid 657 40 2 0.31 0.04, 1.08
Total 2626 150 5 0.19 0.06, 0.46
https://doi.org/10.1371/journal.pntd.0006004.t004
The two main mosquito species observed in the study sites were Culex quinquefasciatus and
An. gambiae s.l. The higher proportion of An. coluzzii (formally the M form of An. gambiae)
could be explained by the fact that these prefer ephemeral breeding sites, found more in urban
and arid areas compared to An. gambiae s.s [30].
The study demonstrated the presence of An. gambiae s.l (principally An. coluzzi) and Culex
quinquefasciatus specimens containing DNA of W. bancrofti in urban settings of Kano state.
The prevalence of W. bancrofti DNA in Culex species from Fagge, Nasarawa and Ungogo
LGAs were low (0.65%, 0.48% and 0.19% respectively) compared to An. gambiae in which
0.96%, 6.78% and 4.55% DNA positivity were recorded respectively. Despite these levels of W.
bancrofti DNA prevalence, we are unable to confirm transmission by An. gambiae and Culex
quinquefasciatus as vectors of W. bancrofti in Kano because the detection of parasite DNA in
mosquitoes does not necessarily imply that LF transmission is ongoing in a given setting. Stud-
ies have shown that mosquitoes that fed on people with very low levels of MF sometimes ingest
MF but rarely produced infective larvae [27]. In Fagge LGA, a low DNA detection level
(0.69%) was recorded after processing 586 specimens of An. gambiae s.l. To confirm on-going
LF transmission in Ungogo LGA where a high infection rate of W. bancrofti has been reported
within An. gambiae species, the use of newer generation diagnostic tools, such as Wb123 [31],
might prove useful in the identification of current and active transmission in the untreated
population.
Similar to other investigations elsewhere [9,32], this study does point to the fact that molec-
ular xenomonitoring methods are superior to parasitological surveys in humans. Nonetheless,
PLOS Neglected Tropical Diseases | https://doi.org/10.1371/journal.pntd.0006004 October 11, 2017 9 / 15
Evidence against MDA in urban Kano, Nigeria
Table 5. W. bancrofti infection rates in pools of Anopheles and Culex mosquitoes by trapping method.
LGA Species Method No. of mosquitoes Pools examined Pools positive MLE (%) 95% CI
Fagge An. gambiae Exit Trap 346 20 1 0.29 0.009, 1.47
Cx. Gravid Trap 13 1 1 - -
Pyrethrum Spray 227 15 2 0.89 0.11, 3.09
Total 586 36 4 0.69 0.18, 1.77
Culex spp. Exit Trap 311 21 1 0.33 0.01, 1.67
Cx. Gravid Trap 3056 161 20 0.69 0.40, 1.10
Pyrethrum Spray 264 20 1 0.38 0.01, 1.95
Total 3631 202 22 0.64 0.38, 0.99
Nasarawa An. gambiae Exit Trap 19 1 0 - -
Cx. Gravid Trap 0 - - - -
Pyrethrum Spray 18 5 2 24.49 2.69, 74.99
Total 37 6 2 6.78 0.81, 22.66
Culex spp. Exit Trap 25 7 0 - -
Cx. Gravid Trap 2841 147 12 0.44 0.21, 0.79
Pyrethrum Spray 358 24 3 0.87 0.17, 2.51
Total 3224 178 15 0.48 0.26, 0.82
Ungogo An. gambiae Exit Trap 326 20 11 4.63 2.16, 8.50
Cx. Gravid Trap 14 4 0 - -
Pyrethrum Spray 84 6 3 5.44 1.04, 16.10
Total 424 30 14 4.55 2.34, 7.85
Culex. spp Exit Trap 737 26 0 - -
Cx. Gravid Trap 1605 90 4 0.25 0.06, 0.65
Pyrethrum Spray 284 34 1 0.17 0.005, 0.89
Total 2626 150 5 0.19 0.06, 0.46
https://doi.org/10.1371/journal.pntd.0006004.t005
defining the elimination thresholds using molecular xenomonitoring requires defining at
which prevalence estimate, in mosquitoes, transmission can be said to be interrupted. The
observed prevalence of parasite DNA in the mosquitoes fall within the cut-off points of 0.25%,
0.5% and 1% suggested for Culex areas [33–35], and 0.65% and 1.0% for Anopheles areas
[13,36]. However, these cut-offs are only suggestive. The challenge therefore is to clearly define
the elimination thresholds in vectors considering, vector control activities, vector species and
abundance, biting rates etc.
A limitation to this survey was the inability to attain the required sample sizes, and as such,
the wide confidence intervals, especially in the Anopheles collections indicate the need for
much larger sample sizes. This could be due to the period of mosquito collection, as the mos-
quitoes were collected mostly during the dry season. As such the timing of xenomonitoring
surveys, barring programmatic difficulties, is very important to make meaningful assessments.
While Anopheles species are considered the major vectors of W. bancrofti in West Africa, ear-
lier studies in rural settings of Kano State revealed L3 W. bancrofti infection in Culex
Table 6. Distribution of members of the An. gambiae complex in the study sites.
LGA No. analyzed An. coluzzii (M Form) An. gambiae s.s (S Form) M/S An. arabiensis
Fagge 100 99 0 0 1
Nasarawa 35 34 1 0 0
Ungogo 100 99 0 1 0
https://doi.org/10.1371/journal.pntd.0006004.t006
PLOS Neglected Tropical Diseases | https://doi.org/10.1371/journal.pntd.0006004 October 11, 2017 10 / 15
Evidence against MDA in urban Kano, Nigeria
quinquefasciatus [11]. Other studies elsewhere in Nigeria also revealed high infection and
infectivity rates in Culex mosquitoes [37,38]. The identification of DNA of the parasite in both
mosquito genera goes to lend support to these earlier findings. Further, An. coluzzii is believed
to be a more efficient vector of LF compared to An. gambiae s.s [39,40], and the predominant
nature of the former could imply a more efficient transmission of LF in the study locations.
However, the promotion of environmental sanitation, coupled with vector control measures
would go a long way in reducing LF infection and transmission. It is note-worthy that while
the parasitological survey did not detect any infection, entomological surveys targeted at mos-
quito breeding sites identified infections, indicating these as being more sensitive in detecting
any ongoing transmission. The parasitological surveys would also have identified infections in
the community, if these were targeted at high-risk individuals such as those living in the vicin-
ity of those breeding sites. Future assessments should therefore aim at identifying such individ-
uals and stratifying the study communities so as to improve the outcome of parasitological
surveys.
The higher local prevalence of infection observed in the mosquitoes, compared to lower
aggregated values may reflect the spatial heterogeneity and clustering of LF prevalence and
transmission [41,42]. Analyzing disaggregated data to the trap level (especially if the coordi-
nates of trapping sites were taken) might have been useful in identifying focal areas of trans-
mission, considering that mosquitoes have limited flight ranges. This study also reveals the
utility of analyzing mosquitoes that have recently fed in determining mosquito infection preva-
lence [13]. As can be seen from Table 4, fed and gravid mosquitoes generally had higher infec-
tion levels compared to unfed mosquitoes. While some pools of unfed mosquitoes were found
positive, parity dissection were not done in this study. This is because the mosquitoes sent to
the NMIMR were stored dry on silica gel, and parity dissections are best done on fresh sam-
ples. Thus, the positive unfed mosquitoes may represent parous mosquitoes. Filaria DNA can
be detected in mosquitoes that have processed W. bancrofti infected blood [43] and it is there-
fore important that molecular xenomonitoring studies aimed at analyzing unfed mosquitoes,
limit these analyses to parous mosquitoes in order to minimize cost. Further the analysis based
on the trapping methods (Table 5) reveal that trapping of indoor resting mosquitoes using the
PSC and gravid mosquitoes may be better tools in xenomonitoring than exit traps.
Assessing W. bancrofti DNA within mosquito specimens is an indicator of the presence of
infected humans and possible ongoing transmission [41,44]. However, confirming the trans-
mission of LF requires the identification of infective stage larvae either through molecular
methods or through dissection. While our results revealed widespread presence of W. bancrofti
DNA in the mosquito population, we were unable to find a single positive mosquito given the
number of mosquitoes dissected. Even though PCR is far more sensitive than dissection [13], a
limitation of this study is that the mosquitoes dissected for W. bancrofti larvae were not also
subjected to the more sensitive molecular analysis. Such mosquitoes were teased, examined
and discarded, and only un-dissected mosquitoes were shipped to the NMIMR for analyses.
Additionally, assessing W. bancrofti DNA within mosquitoes is not a good indicator to con-
firm the presence of L3 larvae of LF parasite. But due to financial and logistic challenges related
to assessment of the infectivity–L3 –rate (because mosquito specimens should be stored with
RNA processed through real time PCR technique) we were not able to evaluate the infectivity
rate. Molecular xenomonitoring, however, proved more effective in this study and has also
been shown to be a promising tool in post-MDA surveillance [32,33].
In conclusion, despite the fact that infection of W. bancrofti DNA within Anopheles gambiae
specimens was above 1% in some areas, the decline in antigen prevalence from the 2010 survey
to the current survey led to the conclusion that LF transmission is not sustainable in the three
urban LGAs of Kano state. While the mosquito biting rate could not be determined in this
PLOS Neglected Tropical Diseases | https://doi.org/10.1371/journal.pntd.0006004 October 11, 2017 11 / 15
Evidence against MDA in urban Kano, Nigeria
study, it is believed that the low numbers of An. gambiae collected is not sufficient to sustain
transmission, as studies suggest that 2700 to over 100,000 infective bites are required for a new
infection to be established [45]. The increased use and coverage of insecticide treated nets [28],
and other activities such as mosquito-proofing houses with screens and ceilings [46], will lead
to a reduction in the indoor densities of mosquitoes. These in turn will further decrease the
vector-human contact in these urban areas, and ultimately the inefficient transmission of the
parasite by mosquitoes. Based on these we could not recommend MDA. However, the Federal
Ministry of Health advised that two rounds of MDA should be undertaken. The first round of
MDA was undertaken in 2016. This study demonstrated that entomological surveys are proba-
bly more sensitive indicators of the presence of infection. However, we could not demonstrate
evidence for active transmission as we did not assess the infectivity rate for technical reasons.
While no individual was found positive for antigen in the sample population surveyed, it is
possible that antigen positive and potentially microfilaremic adults could potentially be con-
tributing to transmission, especially since positive mosquitoes were detected. The use of the
wb123 antibody assays may provide further evidence to the presence or absence of active trans-
mission. Re-assessing the prevalence of W. bancrofti infection (both in the human and mos-
quito population) after a couple of years is recommended.
Acknowledgments
We are grateful to the leaders and inhabitants of the study communities and the field/research
assistants who carried out the fieldwork.
Author Contributions
Conceptualization: Dung D. Pam, Susan D’Souza, Safiya Sanda, Ibrahim Nazaradden, Ifeoma
N. Anagbogu, Elisabeth Elhassan, David H. Molyneux, Moses J. Bockarie, Benjamin G.
Koudou.
Formal analysis: Dung D. Pam, Dziedzom K. de Souza, Millicent Opoku.
Funding acquisition: Susan D’Souza, Safiya Sanda, Ibrahim Nazaradden, Elisabeth Elhassan,
David H. Molyneux, Moses J. Bockarie, Benjamin G. Koudou.
Investigation: Dung D. Pam, Dziedzom K. de Souza, Millicent Opoku, Ifeoma N. Anagbogu,
Chukwu Okoronkwo, Emmanuel Davies.
Methodology: Dziedzom K. de Souza, Benjamin G. Koudou.
Project administration: Safiya Sanda, Ibrahim Nazaradden.
Resources: Dziedzom K. de Souza.
Supervision: Dung D. Pam, Ibrahim Nazaradden.
Writing – original draft: Dung D. Pam.
Writing – review & editing: Dung D. Pam, Dziedzom K. de Souza, Susan D’Souza, Millicent
Opoku, Safiya Sanda, Ibrahim Nazaradden, Ifeoma N. Anagbogu, Chukwu Okoronkwo,
Emmanuel Davies, Elisabeth Elhassan, David H. Molyneux, Moses J. Bockarie, Benjamin
G. Koudou.
References
1. Ottesen EA, Duke BO, Karam M, Behbehani K (1997) Strategies and tools for the control/elimination of
lymphatic filariasis. Bull World Health Organ 75: 491–503. PMID: 9509621
PLOS Neglected Tropical Diseases | https://doi.org/10.1371/journal.pntd.0006004 October 11, 2017 12 / 15
Evidence against MDA in urban Kano, Nigeria
2. Simonsen PE, Mwakitalu ME (2013) Urban lymphatic filariasis. Parasitol Res 112: 35–44. https://doi.
org/10.1007/s00436-012-3226-x PMID: 23239094
3. WHO (2015) Global programme to eliminate lymphatic filariasis: progress report, 2014. Weekly epide-
miological record / Health Section of the Secretariat of the League of Nations 90(38): 489–504.
4. Wijesinghe RS, Wickremasinghe AR, Ekanayake S, Perera MS (2007) Physical disability and psycho-
social impact due to chronic filarial lymphoedema in Sri Lanka. Filaria J 6: 4. https://doi.org/10.1186/
1475-2883-6-4 PMID: 17391538
5. Ottesen EA, Hooper PJ, Bradley M, Biswas G (2008) The Global Programme to Eliminate Lymphatic
Filariasis: Health Impact after 8 Years. PLoS Negl Trop Dis 2: e317. https://doi.org/10.1371/journal.
pntd.0000317 PMID: 18841205
6. Molyneux DH, Savioli L, Engels D (2017) Neglected tropical diseases: progress towards addressing the
chronic pandemic. The Lancet 389: 312–325.
7. Addiss D GAELF (2010) The 6th Meeting of the Global Alliance to Eliminate Lymphatic Filariasis: A
half-time review of lymphatic filariasis elimination and its integration with the control of other neglected
tropical diseases. Parasites and Vectors 3: 100. https://doi.org/10.1186/1756-3305-3-100 PMID:
20961435
8. de Souza DK, Sesay S, Moore MG, Ansumana R, Narh CA, et al. (2014) No Evidence for Lymphatic Fil-
ariasis Transmission in Big Cities Affected by Conflict Related Rural-Urban Migration in Sierra Leone
and Liberia. PLoS Negl Trop Dis 8: e2700. https://doi.org/10.1371/journal.pntd.0002700 PMID:
24516686
9. Kouassi BL, de Souza DK, Goepogui A, Narh CA, King SA, et al. (2015) Assessing the presence of
Wuchereria bancrofti in vector and human populations from urban communities in Conakry, Guinea.
Parasites & Vectors 8: 492.
10. WHO (2000) Operational guidelines for rapid mapping of bancroftian filariasis in Africa. WHO/CDS/
CPE/CEE/2000.9. Geneva, Switzerland: World Health Organization.
11. Dogara M, Nock H, Agbede R, Ndams S, Joseph K (2012) Entomological Survey of Mosquitoes
Responsible for the Tranmission of Lymphatic Filariasis in Three Endemic Villages of Kano State, Nige-
ria. The Internet Journal of World Health and Societal Politics 7.
12. WHO (2011) Monitoring and epidemiological assessment of mass drug administration in the global pro-
gramme to eliminate lymphatic filariasis: a manual for national elimination programmes. Geneva:
WHO. 1–79 p.
13. WHO (2009) The role of polymerase chain reaction techniques for assessing lymphatic filariasis trans-
mission. WHO/HTM/NTD/PCT/20091: 1–59.
14. Barbosa RM, Souto A, Eiras AE, Regis L (2007) Laboratory and field evaluation of an oviposition trap
for Culex quinquefasciatus(Diptera: Culicidae). Memórias do Instituto Oswaldo Cruz 102: 523–529.
PMID: 17612774
15. de Souza DK, Koudou BG, Bolay FK, Boakye DA, Bockarie MJ (2013) Filling the Gap 115 Years after
Ronald Ross: The Distribution of the Anopheles coluzzii and Anopheles gambiae s.s from Freetown
and Monrovia, West Africa. PLoS ONE 8: e64939. https://doi.org/10.1371/journal.pone.0064939
PMID: 23741429
16. de Souza DK, Koudou B, Kelly-Hope L, Wilson MD, Bockarie MJ, et al. (2012) Lymphatic filariasis vec-
tors and the implications for accelerated elimination of Anopheles-transmitted filariasis in West Africa.
Parasites & Vectors 5: 259.
17. Ramzy RM (2002) Field application of PCR-based assays for monitoring Wuchereria bancrofti infection
in Africa. Ann Trop Med Parasitol 96 Suppl 2: S55–59.
18. Fischer P, Wibowo H, Pischke S, Ruckert P, Liebau E, et al. (2002) PCR-based detection and identifica-
tion of the filarial parasite Brugia timori from Alor Island, Indonesia. Ann Trop Med Parasitol 96: 809–
821. https://doi.org/10.1179/000349802125002239 PMID: 12625936
19. Gillies MT, Coetzee M (1987) A supplement to the Anophelinae of Africa south of the Sahara. S Afr Inst
Med Res 55: 1–143.
20. Gillies MT, De Meillon B (1968) The Anophelinae of Africa South of the Sahara (Ethiopian Zoographical
Region). South African Institute for Medical Research, Johannesburg 54: 343.
21. Fanello C, Santolamazza F, della Torre A (2002) Simultaneous identification of species and molecular
forms of the Anopheles gambiae complex by PCR-RFLP. Med Vet Entomol 16: 461–464. PMID:
12510902
22. Takagi H, Itoh M, Kasai S, Yahathugoda TC, Weerasooriya MV, et al. (2011) Development of loop-
mediated isothermal amplification method for detecting Wuchereria bancrofti DNA in human blood and
vector mosquitoes. Parasitology International 60: 493–497. https://doi.org/10.1016/j.parint.2011.08.
018 PMID: 21930238
PLOS Neglected Tropical Diseases | https://doi.org/10.1371/journal.pntd.0006004 October 11, 2017 13 / 15
Evidence against MDA in urban Kano, Nigeria
23. Ramzy RMR, Farid HA, Kamal IH, Ibrahim GH, Morsy ZS, et al. (1997) A polymerase chain reaction-
based assay for detection of Wuchereria bancrofti in human blood and Culex pipiens. Trans R Soc Trop
Med Hyg 91: 156–160. PMID: 9196756
24. Katholi C, Toé L, Merriweather A, Unnasch T (1995) Determining the prevalence of Onchocerca volvu-
lus infection in vector populations by PCR screening of pools of black flies. J Infect Dis 172: 1414–
1417. PMID: 7594692
25. Katholi CR, Unnasch TR (2006) Important experimental parameters for determining infection rates in
arthropod vectors using pool screening approaches. Am J Trop Med Hyg 74: 779–785. PMID:
16687680
26. Kelly-Hope LA, Molyneux DH, Bockarie MJ (2013) Can malaria vector control accelerate the interrup-
tion of lymphatic filariasis transmission in Africa; capturing a window of opportunity?. Parasites & Vec-
tors 6: 39.
27. Bockarie MJ, Pedersen EM, White GB, Michael E (2009) Role of vector control in the global program to
eliminate lymphatic filariasis. Annu Rev Entomol 54.
28. Garley AE, Ivanovich E, Eckert E, Negroustoueva S, Ye Y (2013) Gender differences in the use of
insecticide-treated nets after a universal free distribution campaign in Kano State, Nigeria: post-cam-
paign survey results. Malaria Journal 12: 119–119. https://doi.org/10.1186/1475-2875-12-119 PMID:
23574987
29. Internal Displaced Monitoring Centre and the Norwegian Refugee Council (2014) Global Overview
2014 Report: people internally displaced by conflict and violence. In: Lennard J, editor. Geneva:
Imprimerie Harder.
30. de Souza D, Kelly-Hope L, Lawson B, Wilson M, Boakye D (2010) Environmental Factors Associated
with the Distribution of Anopheles gambiae s.s in Ghana; an Important Vector of Lymphatic Filariasis
and Malaria. PloS One 5: e9927. https://doi.org/10.1371/journal.pone.0009927 PMID: 20360950
31. Steel C, Golden A, Kubofcik J, LaRue N, de Los Santos T, et al. (2013) Rapid Wuchereria bancrofti-spe-
cific antigen Wb123-based IgG4 immunoassays as tools for surveillance following mass drug adminis-
tration programs on lymphatic filariasis. Clin Vaccine Immunol 20: 1155–1161. https://doi.org/10.1128/
CVI.00252-13 PMID: 23740923
32. Rao RU, Samarasekera SD, Nagodavithana KC, Punchihewa MW, Dassanayaka TDM, et al. (2016)
Programmatic Use of Molecular Xenomonitoring at the Level of Evaluation Units to Assess Persistence
of Lymphatic Filariasis in Sri Lanka. PLOS Neglected Tropical Diseases 10: e0004722. https://doi.org/
10.1371/journal.pntd.0004722 PMID: 27196431
33. Rao RU, Nagodavithana KC, Samarasekera SD, Wijegunawardana AD, Premakumara WDY, et al.
(2014) A Comprehensive Assessment of Lymphatic Filariasis in Sri Lanka Six Years after Cessation of
Mass Drug Administration. PLoS Negl Trop Dis 8: e3281. https://doi.org/10.1371/journal.pntd.0003281
PMID: 25393404
34. Farid HA, Morsy ZS, Helmy H, Ramzy RMR, Setouhy ME, et al. (2007) A Critical Appraisal of Molecular
Xenomonitoring as a Tool for Assessing Progress toward Elimination of Lymphatic Filariasis. The Amer-
ican journal of tropical medicine and hygiene 77: 593–600. PMID: 17978055
35. Michael E, Malecela-Lazaro MN, Kabali C, Snow LC, Kazura JW (2006) Mathematical models and lym-
phatic filariasis control: endpoints and optimal interventions. Trends in Parasitology 22: 226–233.
https://doi.org/10.1016/j.pt.2006.03.005 PMID: 16564745
36. Pederson EM, Stolk WA, Laney SJ, Michael E (2009) The role of monitoring mosquito infection in the
global programme to eliminate lymphatic filariasis. Trends Parasitol 25: 319–327. https://doi.org/10.
1016/j.pt.2009.03.013 PMID: 19559649
37. Udonsi JK (1988) Bancroftian filariasis in the Igwun Basin, Nigeria. An epidemiological, parasitological,
and clinical study in relation to the transmission dynamics. Acta Tropica 45: 171–179. PMID: 2901204
38. Anosike JC, Nwoke BE, Ajayi EG, Onwuliri CO, Okoro OU, et al. (2005) Lymphatic filariasis among the
Ezza people of Ebonyi State, Eastern Nigeria. Ann Agric Environ Med 12: 181–186. PMID: 16457471
39. Hunter JM (1992) Elephantiasis: a disease of development in north east Ghana. Social Science and
Medicine 35: 627–645. PMID: 1359648
40. Amuzu H, Wilson M, Boakye D (2010) Studies of Anopheles gambiae s.l (Diptera: Culicidae) exhibiting
different vectorial capacities in lymphatic filariasis transmission in the Gomoa district, Ghana. Parasites
& Vectors 3: 85.
41. Gambhir M, Bockarie M, Tisch D, Kazura J, Remais J, et al. (2010) Geographic and ecologic heteroge-
neity in elimination thresholds for the major vector-borne helminthic disease, lymphatic filariasis. BMC
Biology 8: 22. https://doi.org/10.1186/1741-7007-8-22 PMID: 20236528
PLOS Neglected Tropical Diseases | https://doi.org/10.1371/journal.pntd.0006004 October 11, 2017 14 / 15
Evidence against MDA in urban Kano, Nigeria
42. Joseph H, Moloney J, Maiava F, McClintock S, Lammie P, et al. (2010) First evidence of spatial cluster-
ing of lymphatic filariasis in an Aedes polynesiensis endemic area. Acta Tropica 120 (Supplement 1):
S29–S47.
43. Pilotte N, Zaky WI, Abrams BP, Chadee DD, Williams SA (2016) A Novel Xenomonitoring Technique
Using Mosquito Excreta/Feces for the Detection of Filarial Parasites and Malaria. PLoS Neglected Trop-
ical Diseases 10: 1–14.
44. de Souza DK, Ansumana R, Sessay S, Conteh A, Koudou B, et al. (2015) The impact of residual infec-
tions on Anopheles-transmitted Wuchereria bancrofti after multiple rounds of mass drug administration.
Parasites & Vectors 8: 1–8.
45. Southgate BA (1984) Recent advances in the epidemiology and control of filarial infections including
entomological aspects of transmission. Trans R Soc Trop Med Hyg 78: 19–27.
46. Ogoma SB, Lweitoijera DW, Ngonyani H, Furer B, Russell TL, et al. (2010) Screening mosquito house
entry points as a potential method for integrated control of endophagic filariasis, arbovirus and malaria
vectors. PLoS Negl Trop Dis 4: e773. https://doi.org/10.1371/journal.pntd.0000773 PMID: 20689815
PLOS Neglected Tropical Diseases | https://doi.org/10.1371/journal.pntd.0006004 October 11, 2017 15 / 15