A Comparative Study of Human Landing Catches and Pyrethrum Spray Catches Used in Malaria Vector Studies in the Kasena Nankana District (KND) of Ghana

Abstract

The most direct and reliable method for estimating the man-biting rate is the human landing catches (HLC). It is considered the most representative and usually considered as the “Gold standard”, for determining human biting activity of mosquitoes. However, of recent there has been concerns about the ethics of using humans as baits to collect mosquitoes and therefore there is the need for an alternative method. This study compared Human Landing and Pyrethrum Spray methods in estimating malaria transmission intensity in an irrigated area in Kassena Nankana District of Northern Ghana. Both methods were used to collect mosquitoes during the wet and dry seasons of 2001-2002. Man biting rates, sporozoite rates and Entomological inoculation rates (EIR) were estimated for both methods. Using Human landing catches with a total of 192 man-nights of yielded 59.8% (6270) of Anopheles gambiae s.I., whereas Pyrethrum spray catches (PSC) contributed 40.2% (4220). Biting rates estimated from HLC during the wet season were significantly higher (P<0.05) than that of the dry season (60.9 versus 26.6), whereas, rates from PSC during the wet and dry seasons were not different (P>0.05). There were significant differences (P<0.05) between the biting rates obtained for Anopheles funestus for the two seasons using both methods. The overall sporozoite rate estimated using PSC, 7.1% (29/407) was significantly higher (P<0.05) than 4.9% (204/4353) for HLC. EIR per year using HLC was 123.9 and 1323.0 infective bites/ man/ year for the dry and wet seasons respectively while, it was 34.3 and 52.3 respectively using PSC. The annual EIR estimated for the two vectors, Anopheles gambiae and Anopheles funestus from HLC were similar (731 vrs 517.9) whilst that estimated from PSC was higher for Anopheles gambiae than Anopheles funestus (36.0 vrs 13.0). Although the estimated values using the two methods varied considerably, the transmission patterns were similar. In areas where mosquito numbers may be very low, for example, in the dry season, PSC may be useful in the assessment of malaria transmission intensity. The study provides information on the comparative use of HLC and PSC in vector transmission studies, which is necessary for the planning and implementation of future vector control strategies.