Impact of cyfluthrin (Solfac EW050) impregnated bed nets on malaria transmission in the city of Mbandjock : lessons for the nationwide distribution of long-lasting insecticidal nets (LLINs) in Cameroon.

BACKGROUND: Insecticide treated materials remain the mainstay for malaria prevention. The current study reports on the entomological impact of cyfluthrin impregnated bed nets on malaria transmission in Mbandjock, a semi urban locality in southern Cameroon. Several findings pertaining to the recent distribution of LLINs across Cameroon are discussed. METHODS: Malaria transmission and vector bionomics were monitored before and after impregnated net coverage. Bed nets were distributed in Mbandjock, whereas the locality of Nkoteng was free of bed nets during the entire study period. January to June 1997 represented the period before bed net coverage and September 1997 to September 1998 was the period after bed net coverage. Adult mosquitoes were collected by human landing catches. Mosquito genus and species were identified with morphological and molecular diagnostic tools. Anopheline salivary glands and ovaries were dissected to determine female infectious status and parity rates respectively. RESULTS: A total of 6959 anophelines corresponding to 6029 in Mbandjock and 930 in Nkoteng were collected in the course of the study. Seven species were recorded in both cities : Anopheles coustani, An. funestus, An. gambiae sl, An. moucheti, An. ziemanni, An. nili and An. paludis. An. gambiae s.l. (>95% An. gambiae S molecular form) was the most abundant species representing 75.6% and 86.6% of the total anophelines caught in Mbandjock before and after bed net coverage respectively. The human biting rate (HBR) in Mbandjock decreased from 17 bites/human/night before bed net coverage to less than 4 bites/human/night during the first 7 months following impregnated bed net coverage. A significant decrease of mosquito parity rate was recorded when comparing the period before (52%) and after (46.5%) bed net distribution. The average infection rate of malaria vectors significantly decreased from 5.3% before to 1.8% after bed net coverage (p < 0.0001). The entomological inoculation rate in Mbandjock was reduced by 74% varying from 124.1 infected bites/human/year before bed net distribution, to 32.5 infected bites/human/year after bed net coverage. All entomological indexes were relatively stable in Nkoteng and no reduction of malaria transmission was recorded in this locality. CONCLUSION: The study confirms the effectiveness of cyfluthrin impregnated nets in reducing malaria transmission. Lessons from this study could be essential to draw guidelines for the management of the recent nationwide distribution of LLINs across Cameroon in 2011.

Laboratory colonization of Anopheles pseudopunctipennis (Diptera: Culicidae) without forced mating.

Anopheles pseudopunctipennis is one of the main malaria vectors in the Andean regions of South America. Few experimental data exist on this species because it is not very available in laboratories due to its eurygamic status that makes colony maintenance difficult. Indeed, individuals do not mate in the confined space of insectary cages. To avoid this problem, forced artificial mating can be used. However, this technique is time consuming, requires a well-trained technician, and is inadequate for easy mass production, which is sometimes necessary for certain experimental works. This study presents a technique based on exposure of adult mosquitoes to a blue stroboscopic light for 20 min during several nights, which encourages them to copulate naturally under laboratory conditions. After some generations, a self-free-mating strain was obtained. The technique is simple, inexpensive and is probably effective whatever the An. pseudopunctipennis strain considered.

Host choice and human blood index of Anopheles pseudopunctipennis in a village of the Andean valleys of Bolivia.

BACKGROUND: The Human Blood Index (HBI, proportion of bloodmeals of a mosquito population obtained from man) is relevant to epidemiological assessment and to the modification of measures to interrupt malaria transmission since the vectorial capacity of the vector varies as the square of the HBI. Anopheles pseudopunctipennis is a main malaria vector in South America. Unfortunately, few data exist concerning HBI values in its range of distribution and none from Bolivia where this species is considered as an important malaria vector in the central Andes. METHODS: The host choice of An. pseudopunctipennis has been studied in Mataral, a characteristic village of the central Andes of Bolivia. Mosquito host feeding preference experiments (equal accessibility to host in homogenous environment) were monitored using baited mosquito nets in latin square designs. Host feeding selection experiments (natural feeding pattern in heterogeneous environment) was measured by bloodmeal analysis, using ELISA to determine the origin of blood. Mosquito bloodmeals were collected on various occasions, using various techniques in a variety of sampling sites. A survey of the possible blood sources has also been carried out in the village. Data were analysed with the forage ratio method. RESULTS: An. pseudopunctipennis chooses amongst hosts. Sheep, goats, donkeys and humans are the preferred hosts, while dogs, pigs and chicken are rarely bitten. An. pseudopunctipennis has an opportunistic behaviour, in particular within the preferred hosts. The HBI in Mataral is approximately 40% and in the central Andes, may range from 30-50%, in accordance to other findings. A high proportion of mixed meals were encountered (8%), and cryptic meals are likely more numerous. There was no difference amongst the HBI from parous and nulliparous mosquitoes. CONCLUSION: Forage ratio analysis is a powerful tool to interpret mosquito host choices. However, refinements in sampling strategies are still needed to derive accurate and precise HBIs that could be computed to compare or follow epidemiological situations. The low antropophily of An. pseudopunctipennis, associated with changing environmental conditions, leads to unstable malaria (Plasmodium vivax) transmission in the central Andes. The opportunistic behaviour of this vector may be used to attract mosquitoes to insecticide. Zooprophylaxis is a promising alternative control strategy.

Bioefficacy of cyfluthrin (SOLFAC EW050) impregnated bed-nets against Anopheles gambiae in southern Cameroon.

The bioefficacy of cyfluthrin-impregnated bed-nets was evaluated in the agro-industrial town of Mbandjock (southern Cameroon). The objectives were to assess the knockdown and mortality rates, the protection against bloodfeeding mosquitoes, and the irritant effect of cyfluthrin (SOLFAC EW050)-impregnated bed-nets against a susceptible strain of Anopheles gambiae. Polyester bed-nets were impregnated and distributed to inhabitants of Mbandjock for use, then nets were retreated after 6 months. The uptake of active ingredient on nets ranged from 30.8 mg/m2 to 75.1 mg/m2 at the initial treatment and from 131.0 mg/m2 to 225.0 mg/m2 at retreatment. The susceptible Kisumu reference strain of Anopheles gambiae reared in our laboratory was used for bioassays. The knockdown rate on freshly treated nets (2 wk after treatment) ranged from 93 to 96% and the mortality rate ranged from 52 to 70%. During the 12-month trial, knockdown and mortality rates showed 2 peaks, respectively, in the 4th month (94-97% knockdown and 61-96% mortality) and 7th month (i.e., soon after retreatment; 89-98% knockdown and 86-100% mortality), separated by breakdowns on the 5th through 6th and 12th months (46-77% knockdown and 8-69% mortality). Knockdown and mortality rates decreased faster on the lower part of nets than on the top, suggesting that some external factors such as dirt and daily hand manipulation could impede the efficacy of treated nets. Exceedingly dirty nets were less effective than clean nets. The protective rate against bloodfeeding mosquitoes ranged from 60 to 100% during the 1st 4 months and decreased at 40-70% during the 5th and 6th months after the initial treatment. After retreatment, the protective rate ranged from 50 to 90% for the 1st 5 months and from 35 to 64% at the 6th month. More than 70% of mosquitoes that attempt to feed through treated or retreated nettings died within 24 h after contact. Cyfluthrin was found to be mildly irritant during the whole evaluation. This trial reveals that cyfluthrin EW050-treated nets were effective against a susceptible strain of An. gambiae.