Vector competence, for Wuchereria bancrofti, of the Anopheles populations in the Bongo district of Ghana

The ability of vector mosquitoes to transmit the microfilariae (mff) of Wuchereria bancrofti, especially when the levels of microfilaraemia in the humans on which the mosquitoes are feeding are very low, is very important for understanding the transmission dynamics of lymphatic filariasis. Data on the correlation between vector competence and the microfilarial load in the human host are also relevant to those trying to improve transmission models for this disease. The majority of the relevant studies have involved culicine rather than anopheline vectors. The competence of populations of Anopheles mosquitoes to transmit W. bancrofti in a district in the Upper East region of Ghana has now been investigated. The wild mosquitoes that fed on 20 volunteers under natural conditions were collected hourly during the night, from 21.00 hours on one day to 06.00 hours on the next. Overall, 1348 fed female mosquitoes--665 Anopheles, 662 Culex and 21 Aedes--were collected. Approximately 50% of the mosquitoes caught were killed immediately post-collection and dissected so that the number of W. bancrofti mff each had ingested could be counted. The remaining mosquitoes where dissected when they died (if this was within 12 days of collection) or when they were killed on day 12 post-collection. With the exception of one Culex mosquito that harboured one microfilaria, none of the Culex and Aedes mosquitoes were found infected with W. bancrofti. All of the other mosquitoes found infected were An. gambiae s.l. or An. funestus. When fingerprick samples of blood, collected hourly from the volunteers during the mosquito infection, were used to estimate the microfilaraemias in the blood on which these mosquitoes had fed, microfilarial uptake and the number of developing larvae were found to vary considerably even when the microfilaraemias in the bloodmeal source were similar. The results of a regression analysis on the pooled data for the Anopheles mosquitoes indicated the process of limitation, although larger samples need to be investigated to determine whether this process occurs only in An. gambiae s.l. or An. funestus or in both of these taxa.     

Relationship between malaria and filariasis transmission indices in an endemic area along the Kenyan Coast

BACKGROUND AND OBJECTIVES: An entomological survey was conducted to determine the relationship between malaria and lymphatic filariasis transmission by Anopheles gambiae s.l. and An. funestus in two inland villages along the Kenyan coast. METHODS: Mosquitoes were sampled inside houses by pyrethrum spray sheet collection (PSC). In the laboratory, the mosquitoes were sorted to species, dissected for examination of filarial infection and the anophelines later tested for Plasmodium falciparum circumsporozoite proteins by an enzyme-linked immunosorbent assay (ELISA). RESULTS: From a total of 2,032 female mosquitoes collected indoors, An. gambiae s.l constituted 94.4% while the remaining 5.6% comprised of An. funestus and Culex quinquefasciatus. None of the Cx. quinquefasciatus was positive for filarial worms. P. falciparum sporozoite rate for An. gambiae s.l. from both villages was significantly higher than Wuchereria bancrofti infectivity rate. Similarly, the entomological inoculation rate for An. gambiae s.l. was significantly higher than the corresponding W. bancrofti infective biting rate and transmission potential for both the villages. Mass treatment of people with filaricidal drugs in Shakahola in the ongoing global elimination of lymphatic filariasis campaign seemed to have reduced the indices of filariasis transmission but had no effect on malaria transmission. INTERPRETATION AND CONCLUSION: These results indicate the intensity of malaria transmission by anophelines to be much higher than that of lymphatic filariasis in areas where both diseases co-exist and re-emphasise the need to integrate the control of the two diseases in such areas.     

Impact of insecticide-treated materials on filaria transmission by the various species of vector mosquito in Africa

Nocturnally periodic bancroftian filariasis is maintained by three mainly endophilic vectors in East Africa: Culex quinquefasciatus, Anopheles funestus and the An. gambiae complex. Permethrin-impregnated bednets provide considerable protection against these mosquitoes, but the species respond differently. The degree of protection conferred by treated bednets was determined in Kenyan communities where all three vectors actively transmit Wuchereria bancrofti. The annual transmission potential in the communities (i.e. an estimate of the number of human infective, third-stage larvae of W. bancrofti inoculated into each villager each year) was reduced by 92%, through the nets' impact on vector biting rates (reduced by 22%) and their cumulative impact on the annual infective biting rate (reduced by 95%). Thus a modest reduction in the numbers of mosquitoes biting humans, attributable to the use of the insecticide-treated nets, strongly suppressed the risk of W. bancrofti transmission.     

Bancroftian filariasis: house-to-house variation in the vectors and transmission -- and the relationship to human infection -- in an endemic community of coastal Tanzania

The house-to-house variation in Wuchereria bancrofti vector abundance and transmission intensity, and the relationship of these parameters to human infection, were investigated in an endemic community in coastal Tanzania. Vector mosquitoes were collected in light traps set up in 50 randomly selected households once weekly for 1 year. They were identified, dissected and checked for filarial larvae. Vector densities and transmission potentials varied markedly between households, both for all vectors combined and for the individual vector species (Anopheles gambiae s.1., An. funestus and Culex quinquefasciatus), even between households located close to each other. The variation in vector abundance was probably mainly attributable to differences in the distance to breeding sites, to specific household features likely to ease mosquito entry and hiding, and to the number of household inhabitants. Household annual biting rates (ABR) correlated positively with household annual transmission potentials (ATP), indicating that intense vector biting led to a high transmission intensity. Intriguingly, however, the human filarial-infection status (as indicated by microfilaraemia or circulating filarial antigenemia) did not differ significantly between households with relatively high and lower ABR or ATP. Possible reasons for this result include the long time required for W. bancrofti infection to establish in humans, human behaviour affecting exposure, the sharing of mosquito populations between households, and differential susceptibility of humans to infection. The marked heterogeneity in exposure between households, and the lack of immediate relationship between transmission and detectable human infection at household level, should be taken into account when considering the transmission pattern of lymphatic filariasis.     

Effects of combined diethylcarbamazine and albendazole treatment of bancroftian filariasis on parasite uptake and development in Culex pipiens L

We studied effects of combined diethylcarbamazine (DEC) and albendazole (ALB) treatment on Wuchereria bancrofti microfilaria (MF) uptake and development of infective larvae (L3) in Culex pipiens. Consenting Egyptian adults with microfilaremia (MF > 300/mL) were treated with one or seven daily doses of DEC/ALB. Laboratory-reared mosquitoes were fed on subjects before and after treatment. MF uptake and infectivity (assessed by mosquito dissection) were reduced by 89.6% and 82.9%, respectively, 12 months after single-dose treatment and by 96.2% and 99.7%, respectively, after multi-dose treatment. The L3:mosquito ratio decreased by 88% to 0.082 after single-dose treatment and by 99.8% to 0.001 after multi-dose treatment. If high coverage rates can be achieved for several annual cycles, mass drug administration (MDA) with DEC/ALB has the potential to decrease transmission to unsustainable levels and eliminate filariasis in populations. Multi-dose MDA (especially in the first year) might interrupt transmission with fewer cycles than single-dose treatment.     

The impact of six rounds of single-dose mass administration of diethylcarbamazine or ivermectin on the transmission of Wuchereria bancrofti by Culex quinquefasciatus and its implications for lymphatic filariasis elimination programmes

Lymphatic filariasis (LF) is targeted for global elimination. Transmission interruption through repeated annual single-dose mass administration of anti-filarial drugs is the mainstay of the LF elimination strategy. This study examined the ability of six rounds of mass administration of diethylcarbamazine (DEC) or ivermectin (IVM) to interrupt transmission of Wuchereria bancrofti by Culex quinquefasciatus, the predominant parasite and vector species, respectively. After six rounds of mass drug administration (MDA), received by 54-75% of the eligible population (> or =15 kg body weight), the resting vector infection and infectivity rates fell by 83% and 79% in the DEC arm, 85% and 84% in the IVM arm and 31% and 45% in the placebo arm, respectively. The landing vector infection and infectivity rates fell by 83% and 94% in the DEC arm, 63% and 75% in the IVM arm and 1% each in the placebo arm, respectively. The filarial larval load per resting mosquito declined by 92% and 93% and per landing mosquito by 83% and 69% in the DEC and IVM arms, respectively. The annual infective biting rate (AIBR) fell from 735 to 93 (87%) in the DEC arm, 422 to 102 (76%) in the IVM arm and 472 to 398 (16%) in the placebo arm. The annual transmission potential (ATP) declined from 2514 to 125 (95%), 1212 to 241 (80%) and 1547 to 1402 (9%) in the DEC, IVM and placebo arms, respectively. However, mosquitoes with infection [microfilaria/larva 1/larva 2 (Mf/L1/L2)] were found in all study villages. Three of five villages in the IVM arm and two of five in the DEC arm recorded no resting mosquitoes with infective-stage (L3) larva. Although the ATP, after six rounds of MDA, fell substantially and remained at 125 and 241 in the DEC and IVM arms, respectively, the cumulative exposure to infective stage larvae (ATP) during the treatment period of 6 years was as high as 2995 in the DEC arm and 1522 in the IVM arm, because of considerable level of transmission during the initial (1-3) rounds of MDA. We conclude that (i) six rounds of MDA, even with 54-75% treatment coverage, can reduce LF transmission very appreciably; (ii) better treatment coverage and a few more rounds of MDA may achieve total interruption of transmission; (iii) high vector densities may partly nullify the reductions achieved in vector infection and infectivity rates by MDA and (iv) achievement of 'true zero' Mf prevalence in communities and 0% infection rate (mosquitoes with Mf/L1/L2) in mosquitoes may be necessary to totally interrupt Culex-transmitted LF.     

Impact of long-term ivermectin (Mectizan) on Wuchereria bancrofti and Mansonella perstans infections in Burkina Faso: strategic and policy implications

Parasitological and clinical surveys were used to determine the long-term impact of ivermectin on the prevalence of Wuchereria bancrofti and Mansonella perstans filarial infections, when the drug was given under community-directed-treatment strategies for onchocerciasis control. The study was undertaken in 11 communities in south-western Burkina Faso. Six of the villages investigated had been treated with ivermectin at least once a year for five of 6 years, with a mean coverage of approximately 65% in each round. The other five, adjacent villages, which were matched with the ivermectin-treated communities by size, ethnicity and social and economic activities, had never been treated because they were not endemic for onchocerciasis. Each subject was checked by the microscopical examination of a smear of 'night' blood, by measurement of the level of circulating antigens from adult W. bancrofti, and by clinical examination for hydrocele (if male) and lymphoedema. The prevalences of lymphoedema and hydrocele in the treated villages were similar to those in the untreated. The prevalences and intensities of W. bancrofti and M. perstans microfilaraemia were, however, significantly lower in the ivermectin-treated communities. The implications of this study are discussed in relation to the old Onchocerciasis Control Programme (OCP) and to the ongoing African Programme for Onchocerciasis (APOC), where extensive and sustained ivermectin distribution is planned through community-based treatment programmes. As with onchocerciasis in Africa, the success of annual treatments to control lymphatic filariasis will depend not only on the number of regular rounds of treatment given but on adequate coverages being achieved in each round. Wherever ivermectin is being distributed alone, for onchocerciasis control, its impact on other filarial infections, notably W. bancrofti, should be evaluated routinely. Any opportunity to add donated albendazole to such distributions should be taken, both to limit the transmission of W. bancrofti and for the wider public-health benefits.     

The prevalences of Wuchereria bancrofti antigenaemia in communities given six rounds of treatment with diethylcarbamazine, ivermectin or placebo tablets

The ICT filariasis card test was used to determine the prevalences of Wuchereria bancrofti antigenaemia among villagers in India. Prior to the tests, those living in the 15 study villages had been treated six times, in six rounds of mass treatment (with 54%-75% coverage) spread over 6 years, with single doses of diethylcarbamazine (five villages), ivermectin (five villages) or placebo (five villages). The corresponding overall prevalences (and ranges) of filarial antigenaemia were 20.2% (13.7%-28.6%), 22.6% (15.3%-34.3%) and 25.9% (22.6%-29.3%), respectively. The overall prevalence of antigenaemia in the villages where diethylcarbamazine (DEC) had been distributed (but not that in the 'ivermectin' villages) was significantly lower than that recorded in the 'placebo' villages (z =2.56; P <0.05). The prevalences of antigenaemia among the villagers aged 1-5 years (18.9%, 15.6% and 22.4% in the DEC, ivermectin and placebo villages, respectively) did not differ significantly with treatment (P >0.05). The results indicate that annual mass treatments based on DEC or ivermectin, with 54%-75% treatment coverage, may have only a limited effect on the prevalence of infection with adult W. bancrofti. The possible reasons for the antigenaemias observed are discussed.     

Non-filarial elephantiasis in the Mt. Elgon area (Kapchorwa District) of Uganda

Following reports of a high frequency of elephantiasis in Kwen County (Kapchorwa District) on the slopes of Mt. Elgon in Uganda, a baseline survey for lymphatic filariasis was carried out in three villages in the affected area. Individuals aged 1 year and above were examined for chronic manifestations of lymphatic filariasis, and for specific circulating filarial antigens and microfilariae of Wuchereria bancrofti. Elephantiasis was observed in all age groups from 10 years and above. The overall prevalence was 4.5%, and the prevalence among individuals aged >/=20 years was 8.2%. Males and females were equally affected. However, there were only few cases of hydrocele (overall prevalence in males of 1.0%) and blood examinations were negative for W. bancrofti circulating antigens and microfilariae. Sampling of potential filariasis mosquito vectors revealed low densities of Anopheles gambiae s.l. and An. funestus, and none of these were infected with filarial larvae. In view of the low hydrocele to elephantiasis ratio, the absence of filarial infection in humans and mosquitoes, the high altitude (1500-2200 m above sea level) and the volcanic soil type, it is concluded that elephantiasis seen in this area is not of filarial origin but most likely is due to podoconiosis (endemic non-filarial elephantiasis).     

Dry season refugia of malaria-transmitting mosquitoes in a dry savannah zone of east Africa

Dry season survival of Anopheles funestus, Anopheles gambiae and Anopheles arabiensis in the Kilombero valley a dry savannah zone of east Africa, was investigated with over 400 collections from 23 areas, covering 300 sq km of the valley. Anopheles gambiae was found only in association with humans, in forested areas of high annual rainfall, while An. funestus occurred at high densities at the valley edge where large non-moving bodies of water remained. A large population of An. arabiensis was present along the river system throughout the middle of the valley, and mosquitoes probably derived from this population were occasionally caught in villages bordering the valley. No evidence was obtained of aestivation in any mosquito species. Anopheles gambiae was the most long lived, 6.3% compared to 2.0% of the An. arabiensis and 4% of the An. funestus surviving for four or more gonotrophic cycles, the approximate duration of the extrinsic cycle of most malaria parasites. Oocysts of malaria parasites were found in 5.4% of An. funestus and 2.3% of An. arabiensis from villages. Oocyst rates in An. funestus differed significantly between areas but not between houses within areas. Anopheles funestus is the most important dry season malaria vector in the valley, and remains in foci closely associated with groups of houses. All three species survive at high densities but as otherwise hidden refugia populations.     

Spatial and temporal heterogeneity of Anopheles mosquitoes and Plasmodium falciparum transmission along the Kenyan coast

The seasonal dynamics and spatial distributions of Anopheles mosquitoes and Plasmodium falciparum parasites were studied for one year at 30 villages in Malindi, Kilifi, and Kwale Districts along the coast of Kenya. Anopheline mosquitoes were sampled inside houses at each site once every two months and malaria parasite prevalence in local school children was determined at the end of the entomologic survey. A total of 5,476 Anopheles gambiae s.l. and 3,461 An. funestus were collected. Species in the An. gambiae complex, identified by a polymerase chain reaction, included 81.9% An. gambiae s.s., 12.8% An. arabiensis, and 5.3% An. merus. Anopheles gambiae s.s. contributed most to the transmission of P. falciparum along the coast as a whole, while An. funestus accounted for more than 50% of all transmission in Kwale District. Large spatial heterogeneity of transmission intensity (< 1 up to 120 infective bites per person per year) resulted in correspondingly large and significantly related variations in parasite prevalence (range = 38-83%). Thirty-two percent of the sites (7 of 22 sites) with malaria prevalences ranging from 38% to 70% had annual entomologic inoculation rates (EIR) less than five infective bites per person per year. Anopheles gambiae s.l. and An. funestus densities in Kwale were not significantly influenced by rainfall. However, both were positively correlated with rainfall one and three months previously in Malindi and Kilifi Districts, respectively. These unexpected variations in the relationship between mosquito populations and rainfall suggest environmental heterogeneity in the predominant aquatic habitats in each district. One important conclusion is that the highly non-linear relationship between EIRs and prevalence indicates that the consistent pattern of high prevalence might be governed by substantial variation in transmission intensity measured by entomologic surveys. The field-based estimate of entomologic parameters on a district level does not provide a sensitive indicator of transmission intensity in this study.     

Assessment of combined ivermectin and albendazole for treatment of intestinal helminth and Wuchereria bancrofti infections in Haitian schoolchildren.

This randomized, placebo-controlled trial investigated the efficacy and nutritional benefit of combining chemotherapeutic treatment for intestinal helminths (albendazole) and lymphatic filariasis (ivermectin). Children were infected with Ascaris (29.2%), Trichuris (42.2%), and hookworm (6.9%), with 54.7% of children having one or more of these parasites. Wuchereria bancrofti microfilaria were found in 13.3% of the children. Children were randomly assigned to treatment with placebo, albendazole, ivermectin, or combined therapy. Combination treatment reduced the prevalence of Trichuris infections significantly more than either drug alone. Combination therapy also significantly reduced the prevalence and density of W. bancrofti microfilaremia compared with placebo or ivermectin alone. Only combination therapy resulted in significantly greater gains in height (hookworm-infected children) or weight (Trichuris-infected children) compared with the placebo group. Combined albendazole and ivermectin was a more efficacious treatment for intestinal helminth and W. bancrofti infections in children and resulted in nutritional benefits not found with either drug alone.     

Dynamics and intensity of Wuchereria bancrofti transmission in the savannah and forest regions of Liberia.

In four villages in the savannah and in the rain forest of Liberia, regular assessment of the biting activity and infection rates of anthropophilic mosquitoes have been carried out through full annual cycles. The microfilaremia rates in the localities in the savannah were 18.3% and 20.0% and in those of the forest 10.3% and 12.5%. The all-night catches were performed inside ordinary inhibited houses at monthly or fortnightly intervals. Presence of infective larvae of Wuchereria bancrofti proved Anopheles gambiae, A. funestus and A. nili to be the local vectors. Biting densities were high in the savannah, and low in the forest. From the mosquito catches and the results of their dissections for filarial larvae it could be estimated, that during the observation year a person in the savannah villages would be bitten annually by 18,165 and 36,450 vector mosquitoes respectively, and would receive 236 and 536 infective bites with 570 and 1211 infective larvae. In the two forest villages the number of vector bites per person per year was calculated to be in the order of 6120 and 1102 of which 64 and 8 would be infective bites transmitting 101 and 8 larvae. The findings of considerable differences in transmission intensities between villages of the same bioclimatic zone and of comparable microfilaremia rates indicates instable epidemiological conditions in at least some of the localities investigated.     

Culex quinquefasciatus in Phitsanulok as a possible vector of nocturnally periodic Wuchereria bancrofti transmission in Myanmar immigrants

The present study was undertaken in order to study whether Culex quinquefasciatus collected in Phitsanulok Province can be an insect host for the development of Wuchereria bancrofti larvae. W. bancrofti infected blood from Myanmar workers in Mae Sot, Tak Province was fed to mosquitoes by using the artificial membrane feeding. An infection of W. bancrofti was found with the highest density of L3 in the mosquito thorax on the 14th day after feeding. The infection rate also correlated to the density of microfilaria found in the donor's blood. Our results showed that Cx. quinquefasciatus in Phitsanulok is a possible vector of nocturnally periodic W. bancrofti.     

Contribution of Anopheles funestus, An. gambiae and An. nili (Diptera: Culicidae) to the perennial malaria transmission in the southern and western forest areas of Côte d'Ivoire

The involvement of members of the Anopheles gambiae complex Giles and An. funestus Giles and An. nili Theobald groups in the transmission of Plasmodium falciparum was recently investigated in the villages of Gbatta and Kpéhiri, which lie, respectively, in forest areas in the west and south of C?te d'Ivoire. Adult female mosquitoes were collected, using human landing catches, inside and outside dwellings. After identification and dissection, the heads and thoraces of all the anopheline mosquitoes were tested, in an ELISA, for circumsporozoite protein (CSP). All the female anopheline mosquitoes collected and identified to species using PCR were found to be An. gambiae s.s., An. nili s.s. or An. funestus s.s., with An. gambiae s.s. and An. funestus s.s. predominant in Gbatta but An. nili s.s. the most common species in Kpéhiri. In Gbatta, 3·1% of the female An. gambiae collected, 5·0% of the female An. funestus and 1·8% of the female An. nili were found CSP-positive. The corresponding values in Kpéhiri were even higher, at 5·9%, 6·2% and 2·4%, respectively. The estimated entomological inoculation rates (EIR) were very high: 302 infected bites (139 from An. gambiae, 146 from An. funestus and 17 from An. nili)/person-year in Gbatta and 484 infected bites (204 from An. gambiae, 70 from An. funestus and 210 from An. nili)/person-year in Kpéhiri. In Gbatta, An. gambiae s.s. was responsible for most of the rainy-season transmission while An. funestus became the main malaria vector in the dry seasons. In Kpéhiri, however, An. nili appeared to be the main vector throughout the year, with An. gambiae of secondary importance and An. funestus only becoming a significant vector during the rainy season. Although, in both study sites, intense transmission was therefore occurring and the same three species of anopheline mosquito were present, the relative importance of each mosquito species in the epidemiology of the human malaria at each site differed markedly.     

A simple and rapid DNA extraction method for the detection of Wuchereria bancrofti infection in the vector mosquito,Culex quinquefasciatus by Ssp I PCR assay

A simple, rapid and inexpensive method for the extraction of DNA from filarial vector, Culex quinquefasciatus, useful in Ssp I PCR assay for xenomonitoring of infection with Wuchereria bancrofti is presented. The DNA extracted by this method was found suitable for PCR detection of W. bancrofti infection in pools of 10-30 mosquitoes. The PCR assay employing the simplified DNA extraction method was evaluated for its sensitivity on field caught Cx. quinquefasciatus, in comparison with the conventional dissection and microscopy technique. When assayed on dissection washings of vector mosquitoes the PCR assay detected 45 pools out of 49 dissection positive pools as positive for infection and hence found to be less sensitive than the conventional technique. The reason for detecting four dissection positive pools as negatives by the PCR assay may be due to the loss of a few numbers of parasites (1-3) present in these pools during the transfer of washings of dissected mosquitoes. The PCR assay detected ten out of 72 dissection negative pools as positives, while it did not detect any of the 62 known negative (laboratory reared, uninfected) mosquito pools as positives. When 38 pools (10 mosquitoes/pool) of intact mosquitoes were assessed for infection by each method, the infection rates obtained by the two methods were almost similar (3.35 and 3.01%, respectively, for conventional method and PCR assay). The results thus show that the DNA extraction method, which is simple, rapid, safe and inexpensive, is efficient to generate DNA from vector mosquitoes useful in PCR assay and hence has potential application in xenomonitoring.     

Usage of personal-protection measures against mosquitoes and the low prevalences of Wuchereria bancrofti microfilaraemia in the Indian city of Chennai

The usage of personal-protection measures against mosquitoes and the prevalence of Wuchereria bancrofti microfilaraemia were assessed in different areas of the city of Chennai, a large urban area in southern India. Most of the households investigated (75% to 92%, depending on socio-economic status) used some form of personal protection (such as mosquito coils, vaporizing mats and liquids and mosquito nets). The study households spent a mean (S.D.) of 109.45 (141.65) Indian rupees/month on personal protection, such expenditure increasing significantly with increasing household income (F=2.95; P=0.03). Over the last three decades the prevalence of W. bancrofti microfilaraemia has been slowly declining in Chennai. Most of the 'moderate-income' areas of the city investigated in the present study appeared free of such microfilaraemia, and the prevalences recorded in about half of the low- and very-low-income study areas did not exceed 1.0%. The mean prevalences recorded in the moderate-, low- and very-low-income areas were 0.51%, 1.15% and 1.30%, respectively. Given their very low prevalences of microfilaraemia, relatively good housing, sanitation and health care and extensive use of personal-protection measures, the 100 million Indians living in (mostly urban) moderate- and high-income areas may not require active mass drug administrations (MDA) against lymphatic filariasis. The need to develop simple methods to stratify urban areas, into those that require and those that do not require active MDA, remains. If lymphatic filariasis is to be eliminated from India in a reasonable time-frame, at least as a public-health problem, MDA should now be focused on the poorer localities.     

Application of a polymerase chain reaction-ELISA to detect Wuchereria bancrofti in pools of wild-caught Anopheles punctulatus in a filariasis control area in Papua New Guinea

Chemotherapy-based eradication programs are aimed at stopping transmission of Wuchereria bancrofti by its obligatory mosquito vector. This study compares one year post-treatment W. bancrofti infection rates of Anopheles punctulatus, the main vector of lymphatic filariasis in Papua New Guinea, using traditional dissection techniques and a polymerase chain reaction (PCR)-based ELISA of a parasite-specific Ssp I repeat. A total of 633 mosquitoes in 35 batches were dissected. Six batches contained W. bancrofti-infected mosquitoes, giving a minimum infection rate of 0.9%. This value was not different than the actual infection rate, which was 9 (1.4%) of 633 mosquitoes (P = 0.48). The DNA was extracted from 47 pools containing a mean of 13.2 mosquitoes per pool. A total of 621 mosquitoes were processed for the PCR-ELISA, including 486 caught by human bait and 135 by light trap, which included both dead and live mosquitoes. Of 23 pools of alcohol-preserved human-bait mosquitoes, seven were positive by the PCR-ELISA, giving an infection rate identical to that obtained by dissection of individual mosquitoes (1.4%). The minimum infection rates for pools of light-trap mosquitoes found dead and alive were 2.7% (2 of 74) and 4.9% (3 of 61), respectively. These values did not differ from each other (P = 0.84), but the overall infection rate of light-trap mosquitoes was greater than that of mosquitoes captured by human bait (3.7% versus 1.4%; P = 0.09). These data indicate that the PCR-ELISA of a W. bancrofti Ssp I repeat using pools of mosquitoes is comparable to traditional dissection techniques for monitoring transmission intensity following introduction of mass chemotherapy. This approach may also be useful for rapid and cost-effective assessment of transmission in endemic areas where the frequency of overt lymphatic pathology is low.     

Clinical characteristics of post-treatment reactions to ivermectin/albendazole for Wuchereria bancrofti in a region co-endemic for Mansonella perstans

Post-treatment reactions to single-dose ivermectin (200 microg/kg) and albendazole (400 mg) were studied in a filarial endemic region of Mali. The prevalence of Wuchereria bancrofti in this region was 48.3% (69 of 143), and coinfection with Mansonella perstans was common (30 of 40, 75%). Microfilarial levels of M. perstans correlated positively with age (P = 0.006) and with W. bancrofti microfilarial levels (P = 0.006). Forty individuals (28 infected and 12 uninfected) were treated, with mild post-treatment reactions occurring in 35.7% (7 of 28) of the W. bancrofti-infected subjects. Reaction severity correlated with pretreatment W. bancrofti microfilarial levels (P = 0.001). There were no significant differences in the prevalence or severity of post-treatment reactions in those who were co-infected with M. perstans. It is concluded that co-infection with M. perstans does not significantly alter the post-treatment reaction profile to single-dose ivermectin/albendazole in W. bancrofti infection in this community, and that acute post-treatment reactions should not limit patient compliance in community-based programs to eliminate lymphatic filariasis.     

The rise and fall of malarial sporozoite rates in Anopheles gambiae s.l. and An. funestus in north-eastern Tanzania, between 1934 and 1999.

The proportion of Anopheles mosquitoes found to be carrying Plasmodium sporozoites, usually called the 'malarial sporozoite rate', has often been used as a measure of mosquito infectivity. Although the sporozoite rates found in Anopheles gambiae and An. funestus in Muheza, north-eastern Tanzania, showed a marked decline between the mid-1930s and the mid-1970s, they then began to rise again. This fall and rise in mosquito infectivity is attributed to the widespread use of antimalarial drugs, which initially tended to reduce the infectivity of patients for mosquitoes, and the subsequent development of resistance to these drugs in the malarial parasites. The rise observed in the sporozoite rates in Muheza in the 1980s-1990s may be attributed to widespread resistance of P. falciparum to chloroquine, until recently the drug of choice for the treatment of malaria in Tanzania. Changes in the survival rates, abundance, or predominant species of the mosquito vectors are unlikely to have influenced the pattern observed. The role of antimalarial drugs in malaria transmission risk is discussed.