Bancroftian Filariasis Research Articles

Possibility of Acorus calamus L. rhizome oil as repellent against Culex quinquefasciatus L. mosquito

Culex quinquefasciatus L. is a vector mosquito for bancroftian filariasis in an urban area. One way to prevent the mosquito bites is the use of repellents. The study aims to reveal the potency of Acorus calamus rhizome oil as a repellent against Cx. quinquefasciatus. Experimental 90 mosquitoes were divided into three groups and two groups were treated with different repellents. One group was treated with sari puspa and another group with Calamus rhizome oil. The fluid group was the control group. Each group was treated four times. ANOVA test gave F test > F table, and t test (α = 5%) showed that t test > t table. This statistic test supported a conclusion that Calamus rhizome oil (Acorus calamus L.) was a potential repellent against Cx. quinquefasciatus.

Bancroftian filariasis: effect of repeated treatment with diethylcarbamazine and albendazole on microfilaraemia, antigenaemia and antifilarial antibodies

Diethylcarbamazine/albendazole (DEC/ALB) therapy is widely used in mass drug administration (MDA) programmes aimed at eliminating lymphatic filariasis. We studied the effects of repeated annual treatments with DEC/ALB on Wuchereria bancrofti microfilaraemia, filarial antigenaemia and IgG4 antibodies to Bm14 antigen. Fifty-seven subjects with asymptomatic microfilaraemia were treated with one or seven daily doses of DEC/ALB at time zero. All subjects were re-treated with single-dose DEC/ALB 12, 24 and 36 months later. The two treatment groups had comparable pre-treatment microfilaria counts. Multidose treatment cleared microfilaraemia more effectively than single-dose treatment. Filarial antigen levels decreased equally in both treatment groups. Total antigen clearance was observed in 29.6%, 52.0%, 63.6% and 79.5% of subjects at 12, 24, 36 and 48 months. These clearance rates are much higher than those observed in prior treatment trials with DEC or ivermectin. Antibody levels increased 4 weeks after treatment and then slowly decreased in most subjects. Antibody tests turned negative in 20%, 35%, 39.4% and 52.5% of treated subjects at 12, 24, 36 and 48 months post treatment. These results show that the studied parameters decline at different rates and to differing degrees following DEC/ALB treatment. These findings have important implications regarding strategies for monitoring the effects of MDA in populations.

Concomitant infections of Plasmodium falciparum and Wuchereria bancrofti on the Kenyan coast

BackgroundAnopheles gambiae s.l. and An. funestus are important vectors of malaria and bancroftian filariasis, which occur as co-endemic infections along the Kenyan Coast. However, little is known about the occurrence and prevalence of concomitant infections of the two diseases in mosquito and human populations in these areas. This study reports the prevalence of concomitant infections of Plasmodium falciparum and Wuchereria bancrofti in mosquito and human populations in Jilore and Shakahola villages in Malindi, Kenya.MethodsMosquitoes were sampled inside houses by pyrethrum spray sheet collection (PSC) while blood samples were collected by finger prick technique at the end of entomological survey.ResultsA total of 1,979 female Anopheles mosquitoes comprising of 1,919 Anopheles gambiae s.l and 60 An. funestus were collected. Concomitant infections of P. falciparum sporozoites and filarial worms occurred in 1.1% and 1.6% of An. gambiae s.l collected in Jilore and Shakahola villages respectively. Wuchereria-infected mosquitoes had higher sporozoite rates compared to non-infected mosquitoes, but multiple infections appeared to reduce mosquito survivorship making transmission of such infections rare. None of the persons examined in Shakahola (n = 107) had coinfections of the two parasites, whereas in Jilore (n = 94), out of the 4.3% of individuals harbouring both parasites, 1.2% had P. falciparum gametocytes and microfilariae and could potentially infect the mosquito with both parasites simultaneously.ConclusionConcerted efforts should be made to integrate the control of malaria and bancroftian filariasis in areas where they co-exist.

Periocular filarial lymphoedema

Nine filarial species infect man but the lymphatic dwellers Wuchereria bancrofti, Brugia malayi and the subcutaneous Onchocerca volvulus are responsible for most infections worldwide. The species most commonly involved in lymphatic filariasis are W bancrofti, B malayi and B timori of which bancroftian filariasis is the most frequent. B malayi is mostly confined to South-East Asia [1]. B timori is restricted to Indonesian islands [2]. The common manifestations of lymphatic filariasis include asymptomatic microfilaraemia, early filariasis (filarial fever, lymphadenitis, lymphangitis, funiculitis, epididymitis, filarial orchitis and filarial abscess), chronic obstructive filariasis (lymph node enlargement, thickened lymphatic channels, hydrocele, chyluria, chylocele, chylous ascitis, chylous diarrhoea, elephantiasis and lymphoedema) and occult filariasis (tropical pulmonary eosinophilia, filarial arthritis, diffuse mesangial proliferative glomerulonephritis, pericardial and endomyocardial fibrosis, raised intracranial pressure with nerve palsies and allergic response to helminths leading to vesiculobullous lesions and urticaria). Though involvement of the eye in lymphatic filariasis has been reported, it is rare. We report a rare case of filarial lymphoedema involving the periocular tissues.

Bancroftian filariasis in children and adolescents: clinical–pathological observations in 22 cases from an endemic area

In areas where bancroftian filariasis is endemic, the clinical manifestations of the disease, which are often very varied, appear most frequently during early adulthood or later. In consequence, very little attention, if any, has been given to the signs and symptoms of the disease in childhood. In an attempt to fill this gap, clinical and pathological observations were made, in Brazil, on 22 children (aged 2-15 years) who were infected with Wuchereria bancrofti. There was a predominance of lymph-node involvement. In all but three (14%) of the children (who had adult parasites in their intrascrotal lymphatic vessels), the adult worms were located in the afferent or efferent vessels of draining lymph nodes, predominantly in the inguinal region. None of the patients presented with distal lymphoedema, and the adenopathy was characterized by painless, localized, lymph-node enlargement, without signs of inflammation in the overlying skin. Histologically, the alterations in the lymphatic vessels and surrounding structures were similar to those described in adult patients, and depended essentially on adult-parasite viability. The localization of the adult worms in the paediatric cases was peculiar and distinct from that observed in adult patients, in whom the adult parasites are usually found in extra-nodal lymphatic vessels. In areas endemic for bancroftian filariasis, therefore, filarial infection should be considered as a possible cause of adenopathy. For the differential diagnosis of adenopathy in young patients from endemic areas, the authors recommend the use of ultrasound and other non-invasive diagnostic tools, as alternatives to excisional biopsies, which are often unnecessary in bancroftian filariasis.

A case of exposure to Bancroftian filariasis in a traveller to Thailand

A New Zealander travelling recreationally to Asia became exposed to Bancroftian filariasis. The traveller had presented incidentally with gastrointestinal illness. In addition to diarrhoea, the traveller's symptoms were non-specific and there was no eosinophilia, lymphoedema, lymphangitis, lymphadenitis, or pain. The immunochromatographic test for Wuchereria bancrofti was positive indicating that there was or had been an adult filarial worm. The illness resolved completely following treatment with ivermectin.

Distended Thoracic Duct and Diffuse Lymphangiectasia Caused by Bancroftian Filariasis

3Department of Pathology, Tripler Army Medical Center, Honolulu, HI. ilariasis is a disease endemic to subtropical areas that is rarely encountered in North America. Because this infection rarely occurs in the United States, our knowledge of CT and MRI findings associated with it is limited. To date, the CT and MRI features of filarial lymphangiectasia in a human have not been described. We present a case of diffuse lymphangiectasia in a patient with filariasis as revealed by CT and MRI findings. Case Report A 23-year-old U.S. marine, who was born and raised in Guyana, South America, before emigrating to the United States at age 21, presented to a primary care facility in Japan, his military duty station, with fever and acute abdominal pain radiating to the right groin. Bilateral inguinal adenopathy was found, and a whole-body CT scan revealed what was thought to be diffuse posterior mediastinal, retroperitoneal, pelvic, and inguinal lymphadenopathy. He had no scrotal F

DETECTION AND CHARACTERIZATION OF WOLBACHIA INFECTIONS IN WUCHERERIA BANCROFTI (SPIRURIDA: ONCHOCERCIDAE) VAR. PACIFICA AND AEDES (STEGOMYIA) POLYNESIENSIS (DIPTERA: CULICIDAE)

Despite control programs based on mass drug administration (MDA) of microfilaricidal compounds, Bancroftian lymphatic filariasis remains a problem in French Polynesia. For an alternative strategy to MDA, we investigated the potential role of Wolbachia to control filarial transmission. Wolbachia are intracellular alpha-proteobacteria endosymbionts that infect a broad range of insects and nematodes. These bacteria have a suspected role in the pathogenesis of filariasis. They also may be useful in mosquito control through cytoplasmic incompatibility. To detect and characterize these bacteria in the filarial and mosquito-vectors in French Polynesia, a survey was conducted on field-collected mosquitoes and microfilariae from infected people. Samples were analyzed by a polymerase chain reaction and gene sequencing. The results indicate that these bacteria are widespread. Sequence analysis of the wsp and ftsZ genes positioned the Aedes polynesiensis Wolbachia in cluster A and Wuchereria bancrofti var. pacifica Wolbachia in cluster D. The implications for possible improved treatment and vector control are discussed.

Six new species of the Anopheles leucosphyrus group, reinterpretation of An. elegans and vector implications

Among Oriental anopheline mosquitoes (Diptera: Culicidae), several major vectors of forest malaria belong to the group of Anopheles (Cellia) leucosphyrus Dönitz. We have morphologically examined representative material (> 8000 specimens from seven countries) for taxonomic revision of the Leucosphyrus Group. Six new species are here described from adult, pupal and larval stages (with illustrations of immature stages) and formally named as follows: An. latens n. sp. (= An. leucosphyrus species A of Baimai et al., 1988b), An. cracens n. sp., An. scanloni n. sp., An. baimaii n. sp. (formerly An. dirus species B, C, D, respectively), An. mirans n. sp. and An. recens n. sp. Additionally, An. elegans (James) is redescribed and placed in the complex of An. dirus Peyton & Harrison (comprising An. baimaii, An. cracens, An. dirus, An. elegans, An. nemophilous Peyton and Ramalingam, An. scanloni and An. takasagoensis Morishita) of the Leucosphyrus Subgroup, together with An. baisasi Colless and the An. leucosphyrus complex (comprising An. balabacensis Baisas, An. introlatus Baisas, An. latens and An. leucosphyrus). Hence, the former Elegans Subgroup is renamed the Hackeri Subgroup (comprising An. hackeri Edwards, An. pujutensis Colless, An. recens and An. sulawesi Waktoedi). Distribution data and bionomics of the newly defined species are given, based on new material and published records, with discussion of morphological characters for species distinction and implications for ecology and vector roles of such species. Now these and other members of the Leucosphyrus Group are identifiable, it should be possible to clarify the medical importance and distribution of each species. Those already regarded as vectors of human malaria are: An. baimaii[Bangladesh, China (Yunnan), India (Andamans, Assam, Meghalaya, West Bengal), Myanmar, Thailand]; An. latens[Borneo (where it also transmits Bancroftian filariasis), peninsular Malaysia, Thailand]; probably An. cracens (Sumatra, peninsular Malaysia, Thailand); presumably An. scanloni (Thailand); perhaps An. elegans (the Western Ghat form of An. dirus, restricted to peninsular India); but apparently not An. recens (Sumatra) nor An. mirans[Sri Lanka and south-west India (Karnataka, Kerala, Tamil Nadu)], which is a natural vector of simian malarias. Together with typical An. balabacensis, An. dirus and An. leucosphyrus, therefore, the Leucosphyrus Group includes about seven important vectors of forest malaria, plus at least a dozen species of no known medical importance, with differential specific distributions collectively spanning > 5000 km from India to the Philippines.

Bancroftian filariasis in an endemic area of Brazil: differences between genders during puberty

Gender differences in susceptibility to infectious diseases have been observed in various studies. A survey was performed in a bancroftian filariasis endemic area in the city of Olinda, Brazil. All residents aged 5 years or older were examined by thick blood film. People aged 9 to 16 years were interviewed and also tested for filarial antigenaemia. Data were analyzed by contingency table methods and regression models. The risk of microfilaraemia for males was significantly higher. Among those aged 9 to 16 years, the analysis of gender and filariasis by age showed that boys from 15 to 16 years had a higher risk of infection than girls. No association was found between menarche and filariasis in girls. The data suggest that variations between gender in filariasis could result, at least in part, from an increase in susceptibility of men. This epidemiologic feature needs to be considered while formulating elimination plans.

Bancroftian filariasis: patterns of vector abundance and transmission in two East African communities with different levels of endemicity

Intensive monitoring of Wuchereria bancrofti vector abundance and transmission intensity was carried out in two communities, one with high-level endemicity for bancroftian filariasis (Masaika, Tanzania) and the other with low-level (Kingwede, Kenya), on the East African coast. Mosquitoes were collected in light traps, from 50 randomly selected households in each community, once weekly for 1 year. They were identified, dissected and checked for parity and filarial larvae. Anopheles gambiae s. l., An. funestus and Culex quinquefasciatus transmitted W. bancrofti in the two communities but the importance of each of these taxa differed between the communities and by season. The overall vector densities and transmission intensities were significantly higher in Masaika than in Kingwede (the annual biting rate by 3.7 times and the annual transmission potential by 14.6 times), primarily because of differences in the available breeding sites for the vectors and in the vectorial capacity of the predominant vector species. A marked seasonal variation in vector abundance and transmission potential contributed to the complex transmission pattern in the communities. Generally, these indices were higher during and shortly after the rainy seasons than at other times of the year. Considerable differences in W. bancrofti transmission were thus observed between communities within a relatively small geographical area (mainly because of environmentally-determined differences in vector habitats), and these were reflected in the marked differences in infection level in the human populations. The variation in vector abundance, vector composition and transmission intensity in the two communities is discussed in respect to its cause, its effects, and its significance to those attempting to control bancroftian filariasis.

Changes in the haemocyte population of the mosquito, Culex quinquefasciatus, following infection with the filarial parasite, Wuchereria bancrofti

The mosquito Culex quinquefasciatus Say (Diptera: Culicidae) is the vector of the filarial parasite Wuchereria bancrofti (Cobbold) (Spirurida: Onchocercidae), which causes human bancroftian filariasis. Information on the mosquito humoral response against the filarial parasite during the process of its infection and development is important, as it decides the vector competence of the mosquito. Visible changes in the haemocyte population of mosquito, if any, will be an indicator of the possible humoral factors. The present study was aimed at investigating changes in the populations of various types of haemocytes of Cx. quinquefasciatus following infection with W. bancrofti. On day 2 post-feeding on microfilaraemic blood, the haemolymph perfusate of infected mosquitoes with L1 stage of the parasite showed 44.1% granulocytes, 42% prohaemocytes and 13.9% plasmatocytes, whereas that of the control mosquitoes fed on amicrofilaraemic blood showed 63.4% plasmatocytes, 22.2% prohaemocytes and 14.4% granulocytes. Differences in the population numbers of haemocyte types between the infected and control were significant (P > 0.05). However, the mosquitoes examined on day 6 post-feeding, when the parasite was in L2 stage, did not show any such changes. But, similar changes reappeared on day 12 in mosquitoes with L3 stage of the parasite. The observed haemocyte population changes indicate the possibility of some amount of humoral immune response, through the production of certain immune molecules, in Cx. quinquefasciatus infected with W. bancrofti. The nature and exact role of such a response on the filarial parasite development need further investigation.

Management of filariasis using prediction rules derived from data mining.

The present paper demonstrates the application of CART (classification and regression trees) to control a mosquito vector (Culex quinquefasciatus) for bancroftian filariasis in India. The database on filariasis and a commercially available software CART (Salford systems Inc. USA) were used in this study. Baseline entomological data related to bancroftian filariasis was utilized for deriving prediction rules. The data was categorized into three different aspects, namely (1) mosquito abundance, (2) meteorological and (3) socio-economic details. This data was taken from a database developed for a project entitled "Database management system for the control of bancroftian filariasis" sponsored by Ministry of Communication and Information Technology (MC&IT), Government of India, New Delhi. Predictor variables (maximum temperature, minimum temperature, rain fall, relative humidity, wind speed, house type) were ranked by CART according to their influence on the target variable (month). The approach is useful for forecasting vector (mosquito) densities in forthcoming seasons.

Soluble cellular adhesion molecules, selectins, VEGF and endothelin‐1 in patients with Wuchereria bancrofti infection and association with clinical status

Lymphatic filariasis, a mosquito-transmitted disease commonly known as Bancroftian filariasis, is characterized by debilitating pathology linked to the progression of lymphoedema to a chronic state of elephantiasis. We performed longitudinal measurements of endothelial adhesion and angiogenic molecules in 63 Polynesian patients living in an hyperendemic focus of Wuchereria bancrofti. Decreased serum concentrations of soluble (s-) L selectin (CD62L) were noticed in sera of of patients with chronic conditions (hydrocele and elephantiasis). Chyluria was associated with increased vascular endothelial growth factor (VEGF) levels, whereas elephantiasis presented a high endothelin-1 (ET-1) profile. By contrast, increased serum concentrations of soluble intercellular (sICAM-1, CD54), but not of vascular cell (sVCAM-1, CD106), adhesion molecules were observed in sera of patients with bacterial lymphangitis used as controls. These trends are consistent with the increased permeability of vascular structures, a major clinical feature observed in acute lymphatic pathology (of bacterial or filarial origin), and of fundamental differences in the pathogenesis of hydrocele and elephantiasis. Using markers correlated with the clinical status (high ET-1 and VEGF levels for elephantiasis and chyluria, respectively; low CD62L levels for hydrocoele and elephantiasis) it should be possible to monitor disease progression in lymphatic filariasis.

Impact of two rounds of mass drug administration using diethylcarbamazine combined with albendazole on the prevalence of Brugia timori and of intestinal helminths on Alor Island, Indonesia

BackgroundAnnual mass drug administration (MDA) using diethylcarbamizine (DEC, 6 mg/kg) combined with albendazole (alb, 400 mg) is recommended by the Global Programme to Eliminate Lymphatic Filariasis (GPELF). This strategy has been shown to be efficient in the of control bancroftian filariasis, but data on brugian filariasis as well as on the positive side effects on intestinal helminths are lacking.MethodsThe effect of one selective treatment and two rounds of MDA using DEC and alb on the prevalence and intensity of Brugia timori infection were studied on Alor island using a cross-sectional and a cohort approach. Before the campaign and ten months after each treatment cycle microfilariae (mf) were assessed by filtration of night blood. Before and ten months after MDA, stool samples were collected and the prevalence of intestinal helminths were determined.ResultsIn all, the mf-rate dropped from 26.8% before any treatment to 3.8% following the second MDA. Almost all mf-positive, treated individuals showed very low mf densities. The crude prevalence of hookworm dropped from 25.3% to 5.9%. The reduction of prevalence of Ascaris lumbricoides (32.3% to 27.6%) and Trichuris trichiura (9.4% to 8.9%) was less pronounced. Within a cohort of 226 individuals, which was examined annually, the prevalence of A. lumbricoides dropped from 43.8% to 26.5% and of T. trichiura from 12.8% to 6.6%. The results indicate that this MDA approach reduces not only the mf prevalence of B. timori but also the prevalence of hookworm and to a lesser extent also of A. lumbricoides and T. trichiura.ConclusionThe MDA using DEC and alb as recommended by GPELF is extremely effective for areas with brugian filariasis. The beneficial effect of MDA on intestinal helminths may strengthen the national programme to eliminate lymphatic filariasis in Indonesia and may set resources free which are otherwise used for deworming campaigns of schoolchildren.

Bancroftian filariasis in 12 villages in Kwale district, Coast province, Kenya — variation in clinical and parasitological patterns

As part of a larger study on the effects of permethrin-impregnated bednets on the transmission of Wuchereria bancrofti, subjects from 12 villages in the Coastal province of Kenya, south of Mombasa, were investigated. The aims were to update the epidemiological data and elucidate the spatial distribution of W. bancrofti infection. Samples of night blood from all the villagers aged i 1 year were checked for the parasite, and all the adult villagers (aged >/= 15 years) were clinically examined for elephantiasis and, if male, for hydrocele. Overall, 16.0% of the 6531 villagers checked for microfilariae (mff) were found microfilaraemic, although the prevalence of microfilaraemia in each village varied from 8.1%-27.4%. The geometric mean intensity of infection among the microfilaraemic was 322 mff/ml blood. At village level, intensity of the microfilaraemia was positively correlated with prevalence, indicating that transmission has a major influence on the prevalence of microfilaraemia. Clinical examination of 2481 adults revealed that 2.9% had elephantiasis of the leg and that 19.9% of the adult men (10.8%-30.1% of the men investigated in each village) had hydrocele. Although the overall prevalence of microfilaraemia in the study villages had not changed much since earlier studies in the 1970s, both prevalence and intensity varied distinctly between the study villages. Such geographical variation over relatively short distances appears to be a common but seldom demonstrated feature in the epidemiology of bancroftian filariasis, and the focal nature of the geographical distribution should be carefully considered by those mapping the disease.

Histopathologic Improvement with Lymphedema Management, Léogâne, Haiti

In countries where bancroftian filariasis is endemic, lymphedema of the leg is a public health problem, particularly for women, who are disproportionately affected. We investigated the effect of basic lymphedema management (hygiene, skin care, and lower limb movement and elevation) on the histologic features of lymphedema. A total of 118 skin-punch biopsy specimens were collected from the legs of 91 patients enrolled in a lymphedema treatment clinic in Léogâne, Haiti. Follow-up biopsy specimens were collected from 27 patients succeeds, equals 12 months later. Keratinocyte hyperproliferation, condensed dermal collagen, and mononuclear perivascular infiltrate increased with lymphedema stage, which suggested progressive chronic inflammation and fibrosis. Follow-up biopsies showed reductions in perivascular mononuclear infiltrate in the superficial dermis (41% decrease in prevalence), perivascular fibrosis in the deep dermis (58% decrease), and periadnexal mononuclear infiltrate (53% decrease). These data suggest that the clinical improvement commonly observed with basic lymphedema management has a histologic basis.

The efficacies of affected-limb care with penicillin, diethylcarbamazine, the combination of both drugs or antibiotic ointment, in the prevention of acute adenolymphangitis during bancroftian filariasis

Repeated attacks of adenolymphangitis (ADL) contribute significantly to the progression of chronic lymphoedema in lymphatic filariasis. They are a cause of stigma and, since they may prevent work and require treatment for which payment must be made, of economic loss. The aim of the present study was to improve the treatment of ADL attacks, which is currently mostly empirical. In a double-blind, placebo-controlled, clinical study, 150 subjects who had each suffered at least two ADL attacks in the preceding year were enrolled and randomly allocated to a programme of self-care of the affected limb (after an intensive training programme) and one of five treatments for 12 months. The subjects were supplied with tablets and ointment so that they could take oral penicillin (800 mg/day), oral diethylcarbamazine (DEC; 1 mg/kg.day) or both of these drugs (at the same doses), or apply framycetin ointment to the affected limb, or just take placebo tablets and apply placebo (zinc-oxide) ointment. Placebo tablets and placebo ointment were used so that neither the subjects nor those assessing the responses to treatment were aware of the treatment arm to which each subject had been assigned. The subjects were requested to continue with the affected-limb care after they had stopped taking the tablets and applying the cream, and were followed-up for 24 months from the first treatment.Overall, the mean incidence of ADL attacks decreased from 2.7 episodes/person-year in the pre-treatment year to just 0.38 episode/person-year during the treatment year (P< 0.01). The greatest reduction in incidence was seen in the 58 subjects who received penicillin (with or without DEC). Even in the placebo group, however, the incidence of ADL in the treatment year was significantly lower than that seen in the pre-treatment year, indicating that affected-limb care on its own helps to prevent some attacks. In all groups except the placebo, the incidence of ADL attacks in the year post-treatment exceeded that seen in the treatment year, indicating that chemoprophylaxis needs to be continued for more than a year if such attacks are to be prevented. In most (84%) of the attacks recorded, titres of anti-streptococcal antibodies were seen to be elevated (compared with those recorded during convalescence),indicating that streptococci have a role in the aetiology of ADL. It is recommended that a combination of penicillin prophylaxis and affected-limb care be incorporated into filariasis-control programmes, to decrease morbidity.

Characterization ofWolbachiaInfections and Interspecific Crosses ofAedes(Stegomyia)polynesiensisandAe.(Stegomyia)riversi(Diptera: Culicidae)

Prior studies have identified a complicated pattern of interspecific hybridization between members of the Aedes (Stegomyia) scutellaris (Walker) mosquito group, which includes medically important vectors of bancroftian filariasis and dengue. Here, we report that two members of the group, Aedes polynesiensis Marks and Aedes riversi Bohart & Ingram, are both infected with intracellular Wolbachia bacteria. Sequencing of the Wolbachia wsp gene demonstrates that the infections differ from each other and from Wolbachia infections previously reported in mosquitoes. Aedes polynesiensis is the first mosquito identified with a wMel Wolbachia type. Intraspecific crosses of infected and aposymbiotic lines generated via antibiotic treatment show that the Wolbachia infections in both species cause high levels of cytoplasmic incompatibility. Interspecific crosses show that the two species are reproductively isolated. However, repeating the interspecific crosses with aposymbiotic mosquito strains demonstrates that the Wolbachia infections play a role in preventing hybrid offspring. We discuss Wolbachia infections in relation to better defining the evolutionary relationships and causes of speciation within the group, understanding the basis for the observed east-to-west gradient in filarial refractoriness, and developing novel genetic control measures.

Long-term effect of three different strategies for mass diethylcarbamazine administration in bancroftian filariasis: follow-up at 10 years after treatment

The long-term effect of three different strategies for mass diethylcarbamazine (DEC) administration in bancroftian filariasis was assessed 10 years after start of treatment in three endemic communities in Tanzania. The strategies were the standard 12 day treatment (strategy I); a semi-annual single-dose treatment (strategy II); and a monthly low-dose treatment (strategy III). Treatment was given only during the first year. Following reductions immediately after treatment, overall community microfilaraemia levels were approaching pre-treatment levels in all three communities, 10 years later. In individuals who were microfilaria-positive and treated at baseline, the treatment had a long-term effect on microfilarial intensities, with geometric mean intensities being only 11%, 13% and 2% of pre-treatment levels 10 years later for strategies I, II and III, respectively. This suppressive effect was most pronounced for strategy III, which also cleared microfilaraemia and circulating filarial antigenaemia in a larger proportion of treated individuals than the other strategies. Most of the follow-up individuals who developed microfilaraemia between 2 and 10 years after start of treatment had also been microfilaraemic before treatment, suggesting that reappearance of microfilaraemia may be due to surviving female worms and/or that previously microfilaraemic individuals have a higher chance of reinfection than previously amicrofilaraemic individuals.