Sampling outdoor, resting Anopheles gambiae and other mosquitoes (Diptera: Culicidae) in western Kenya with clay pots.

Clay pots were analyzed as devices for sampling the outdoor resting fraction of Anopheles gambiae Giles (Diptera: Culicidae) and other mosquito species in a rural, western Kenya. Clay pots (Anopheles gambiae resting pots, herein AgREPOTs), outdoor pit shelters, indoor pyrethrum spray collections (PSC), and Colombian curtain exit traps were compared in collections done biweekly for nine intervals from April to June 2005 in 20 housing compounds. Of 10,517 mosquitoes sampled, 4,668 An. gambiae s.l. were sampled in total of which 63% were An. gambiae s.s. (46% female) and 37% were An. arabiensis (66% female). The clay pots were useful and practical for sampling both sexes of An. gambiae s.l. Additionally, 617 An. funestus (58% female) and 5,232 Culex spp. (males and females together) were collected. Temporal changes in abundance of An. gambiae s.l. were similarly revealed by all four sampling methods, indicating that the clay pots could be used as devices to quantify variation in mosquito population density. Dispersion patterns of the different species and sexes fit well the negative binomial distribution, indicating that the mosquitoes were aggregated in distribution. Aside from providing a useful sampling tool, the AgREPOT also may be useful as a delivery vehicle for insecticides or pathogens to males and females that enter and rest in them.

Effect of permethrin-impregnated nets on exiting behavior, blood feeding success, and time of feeding of malaria mosquitoes (Diptera: Culicidae) in western Kenya.

The impact of permethrin-treated bednets on the feeding and house entering/exiting behavior of malaria vectors was assessed in two studies in western Kenya. In one study, matched pairs of houses were allocated randomly to receive bednets or no bednets. Exiting mosquitoes were collected in Colombian curtains hung around half of each house; indoor resting mosquitoes were collected by pyrethrum spray catches. The number of Anopheles gambiae Giles and An. arabiensis Patton estimated to have entered the houses was unaffected by the presence of bednets; Anopheles funestus Giles was less likely to enter a house if bednets were present. Anopheles gambiae and An. funestus were less likely to obtain a blood meal and significantly more likely to exit houses when bednets were present. No difference was detected in An. arabiensis rates of blood feeding and exiting. In a second experiment, hourly night biting collections were done on 13 nights during the rainy season to assess whether village-wide use of permethrin-treated bednets caused a shift in the time of biting of malaria vectors. A statistically significant shift was detected in the biting times of An. gambiae s.l., although the observed differences were small. No change was observed in the hourly distribution of An. funestus biting. Our study demonstrated that, at least in the short-term, bednets reduced human-vector contact and blood feeding success but did not lead to changes in the biting times of the malaria vectors in western Kenya.

Helminth parasites in the intestinal tract of indigenous poultry in parts of Kenya.

A study was carried out on 456 indigenous poultry intestinal specimens from various towns in Kenya to determine the occurrence and distribution of helminth parasites in the intestinal tract of the birds. Of the specimens examined, 414 had parasites whereas the remaining 42 had none, which is an infection rate of 90.78%. The main species of helminths found in the intestines were Raillietina sp. (47.53%), Heterakis gallinarum (21.33%), Ascaridia galli (10.03%), Strongyloides avium (9.96%), Choanotaenia infundibulum (4.61%), Cotugnia digonopora (3.6%), Capillaria sp. (1.5%), Trichostrongylus tenius (1.04%) and Syngamus trachea (0.40%). Most helminths were present in both the mid- and hindguts. Syngamus trachea and C. digonopora were only found in the foregut and midgut, respectively. Although chickens from which the specimens were collected appeard healthy, the high prevalence of helminthiasis observed shows the poor level of helminth infection control practiced by the indigenous poultry keepers in the country, which might affect the health status of the birds and their growth rates. Poultry keepers should be encouraged to prevent, control and treat such cases.

Effect of puparia incubation temperature: increased infection rates of Trypanosoma congolense in Glossina morsitans centralis, G. fuscipes fuscipes and G. brevipalpis.

Puparia of Glossina morsitans centralis (Machado), G.fuscipes fuscipes (Newstead) and G.brevipalpis (Newstead) were incubated at 25 +/- 1 degrees C, 28 +/- 1:25 +/- 1 degrees C, day:night or 29 +/- 1 degrees C throughout the puparial period, and maintained at 70-80% relative humidity. Puparial mortality was higher at 29 than at 25 degrees C (optimum temperature) in all three species, particularly in G.f.fuscipes and G.brevipalpis. Adults of G.m.centralis from puparia incubated at 29 degrees C, and those of this subspecies, G.f.fuscipes and G.brevipalpis from puparia incubated at 28:25 degrees C, day:night or 25 degrees C throughout, were infected as tenerals (27 h old) by feeding them at the same time on goats infected with Trypanosoma congolense (Broden) IL 1180 after the parasites were detected in the wet blood film. Infection rates on day 25 post-infected feed were higher in G.m.centralis from puparia incubated at 29 degrees C and in adults of the three different tsetse species from puparia incubated at 28:25 degrees C, day:night, than in those from puparia incubated at 25 degrees C. However, in G.f.fuscipes the labral and hypopharyngeal infection rates were not significantly different from those of the tsetse produced by puparia kept at 25 degrees C.

Development of an exposure-free bednet trap for sampling Afrotropical malaria vectors.

An exposure-free bednet trap (the 'Mbita trap') for sampling of Afrotropical malaria vectors was developed during preliminary studies of mosquito behaviour around human-occupied bednets. Its mosquito sampling efficiency was compared to the CDC miniature light-trap and human landing catches under semi-field conditions in a screen-walled greenhouse using laboratory-reared Anopheles gambiae Giles sensu stricto (Diptera: Culicidae). When compared in a competitive manner (side by side), the Mbita trap caught 4.1+/-0.5 times as many mosquitoes as the CDC light-trap, hung beside an occupied bednet (P < 0.000 1) and 43.2+/-10% the number caught by human landing catches (P < 0.0001). The ratio of Mbita trap catches to those of the CDC light trap increased with decreasing mosquito density. Mosquito density did not affect the ratio of Mbita trap to human-landing catches. In a non-competitive comparison (each method independent of the other), the Mbita trap caught 89.7+/-10% the number of mosquitoes caught by human landing catches (P < 0.0001) and 1.2+/-0.1 times more mosquitoes than the CDC light trap (P = 0.0008). Differences in Mbita trap performance relative to the human landing catch under noncompetitive vs. competitive conditions were explained by the rate at which each method captured mosquitoes. Such bednet traps do not expose people to potentially infectious mosquito bites and operate passively all night without the need for skilled personnel. This trap is specifically designed to catch host-seeking mosquitoes only and may be an effective, sensitive, user-friendly and economic alternative to existing methods for mosquito surveillance in Africa.

Analysis of genetic variability in Anopheles arabiensis and Anopheles gambiae using microsatellite loci.

We analysed genetic variability in Anopheles arabiensis and Anopheles gambiae populations using microsatellite loci to determine whether the Rift Valley restricts the flow of genes. Deviations from Hardy-Weinberg expectations were significant, and were most likely to be due to the high frequency of null alleles observed. An. arabiensis populations occurring between 40 and 700 km apart across the Eastern arm of the Rift Valley were not differentiated (pair-wise F(ST) range: 0.0033-0.0265, P > 0.05). Neither were An. gambiae populations from Asembo Bay and Ghana (F(ST): 0.0063, P > 0.05) despite a geographical separation of about 5000 km. In contrast, significant differentiation was observed between An. gambiae populations from Asembo Bay and Kilifi (about 700 km apart; F(ST) = 0.1249, P < 0.01), suggesting the presence of a barrier to gene flow.