Human Bancroftian Filariasis Research Articles

Scrotal Filariasis, the Importance of Filarial Dance Sign in Scrotal Ultrasound

Objective: To study the value of the filarial dance sign as a diagnostic sign in scrotal ultrasonography in human Bancroftian filariasis. Methods: We studied 3 patients with scrotal pain, with high-resolution ultrasonography (HRUS) of scrotum including power and color Doppler study. All patients underwent peripheral blood smear. Results: Multiple cystic spaces containing motile echogenic twisted tubular structures were observed in the 3 patients. Peripheral blood smears in the 3 patients confirmed the presence of microfilaria. Mild hydrocele in two patients. Conclusions: HRUS is a useful technique for diagnosing scrotal filariasis in symptomatic patients and is very useful in the follow-up treatment.

Human Lymphatic Filariasis: Genetic Polymorphism of Endothelin-1 and Tumor Necrosis Factor Receptor II Correlates With Development of Chronic Disease

Hydrocele and elephantiasis are 2 clinically very diverse and often mutually exclusive chronic manifestations of human bancroftian filariasis. Plasma levels of endothelin-1 (ET-1), a major angiogenic factor, and tumor necrosis factor receptors (TNFRs) that regulate host inflammation have been associated with development of chronic filariasis, although their genetic basis are not known. We studied polymorphisms of ET-1 (Ala288Ser) and TNFR-II (Met196Arg) genes by means of the polymerase chain reaction confronting 2 pairs primers method and restriction fragment length polymorphism, respectively. Plasma ET-1 level was measured by enzyme-linked immunosorbent assay. Met196Arg genotype frequency of TNFR-II polymorphism was significantly greater in hydrocele patients, compared with elephantiasis patients (OR, 4.34 [95% CI, 2.04-9.20]). Conversely, a significantly high prevalence of the Ala288Ser mutation of ET-1 was observed in elephantiasis patients, compared with hydrocele cases (OR, 2.15 [95% CI, 1.13-4.10]). Decreased plasma ET-1 levels associated significantly with Ala288Ser mutation in the study population. A combined analysis indicated a 23-fold higher risk for developing elephantiasis in individuals with TNFR-II (Met196Met) and ET-1 mutants (Ala288Ser + Ser288Ser). ET-1 (Ala288Ser) and TNFR-II (Met196Arg) polymorphisms are associated with development of one or the other form of chronic disease in bancroftian filariasis.

Protective Immunity in Human Filariasis: A Role for Parasite‐Specific IgA Responses

Filaria-specific antibodies of immunoglobulin (Ig) G, IgE, and IgM isotypes have been correlated with acquired immunity in the literature, but the status of filaria-specific IgA and its role in human filariasis has not been addressed. The present study attempts to fill this lacuna. Both total and filaria-specific IgA to different developmental stages of filarial parasites were quantified by solid-phase immunoassays in 412 clinically and parasitologically defined cases occurring in an area endemic for human bancroftian filariasis in Orissa, India. Compared with other clinical categories, microfilariae carriers were deficient in total as well as filaria-specific IgA. More crucially, significantly high levels were observed in putatively immune control subjects from areas of endemicity. These associations were also related to sex; female subjects in each category displayed higher levels of filaria-specific IgA than did male subjects. The study demonstrates, for the first time, a positive correlation between protective immunity and increased levels of filaria-specific IgA in human bancroftian filariasis. Furthermore, filaria-specific IgA appears to be an immunological window for the sex-related differences in susceptibility to infection observed in human filariasis.

Wuchereria bancrofti: Effect of single and multiple larval inoculations on infection dynamics and development of clinical manifestations in non-human primate Presbytis entellus

We earlier reported the successful experimental transmission of Wuchereria bancrofti from humans to the Indian leaf monkey ( Presbytis entellus) [Misra, S., Tyagi, K., Chatterjee, R.K., 1997. Experimental transmission of nocturnally periodic Wuchereria bancrofti to Indian leaf monkey ( Presbytis entellus). Experimental Parasitology 86,155–157.; Dube, A., Murthy, P.K., Puri, S.K., Misra-Bhattacharya, S., 2004. Presbytis entellus: a primate model for parasitic disease research. Trends in Parasitology 20(8), 358–360.] using a small number of animals. The present study, involving 27 langur monkeys, found the development of pathological manifestations ranging from filarial fever, lymphangitis, lymphadenitis, hydrocoele, and limb edema to minor histopathological changes in tissues after single, double, triple, or multiple inoculations of infective larvae of W. bancrofti recovered from Culex quinquefasciatus fed on human microfilaraemic blood. Thirty-eight percent of the infected langurs developed detectable microfilaraemia in their blood. Single or double larval exposure resulted in better worm establishment than multiple exposures with small numbers of larvae. All of the langurs receiving a single large inoculum and 85.71% of those receiving two inoculations harbored adult parasites. Worm establishment decreased with increasing number of larval inoculations. In all, 60% of infected langurs developed classical gross-pathological symptoms of lymphatic filariasis. Of these, 29.16% developed thickening of the lymphatics, 25% suffered from periodic rise in rectal temperature, and 16.66% developed scrotal swelling with presence of microfilariae in the hydrocoele fluid. Only one out of 25 langurs (4%) developed acute limb edema. It appeared that a single inoculum of a large number of infective larvae was able to induce maximum pathology. Fifty-six percent of the infected langurs acquired a peculiar sitting posture, retracting both the hind limbs, usually after 4–5 months of larval inoculation and eventually resulting in reduced mobility. Oral administration of diethylcarbamazine (citrate) at 12 mg/kg for 12 consecutive days to one langur caused 80% suppression in microfilaraemia on day 8, killing all the adult parasites. Of the two immunosuppressed (cortisone- or prednisolone-treated) male rhesus monkeys included in the study, neither developed any of the above lymphatic symptoms or parasites after receiving larval inoculations on two or three occasions; however, a rise in rectal temperature in one of the animals was noticed. The present study thus reveals that the Indian leaf monkey, P. entellus, may serve as an ideal non-human primate model of human bancroftian filariasis for carrying out longitudinal studies on pathology, host–parasite interactions, and preclinical evaluation of candidate anti-filarial drugs or vaccines.

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.

A 26-year follow-up of bancroftian filariasis in two communities in north-eastern Tanzania.

The results of surveys, for human bancroftian filariasis, carried out in 1975 and 1991 in endemic communities in north-eastern Tanzania have already been reported. In 2001, all consenting individuals from two of these communities (Tawalani and Kwale) were re-surveyed, and many of the individuals examined in the earlier surveys were re-identified. The findings revealed an extraordinarily static pattern of infection and disease over the 26 years of follow-up. By 2001, despite brief interventions introduced after the first two surveys, the community prevalences and mean intensities of microfilaraemia had almost returned to pre-treatment levels. The majority of re-identified individuals who had been found microfilaraemic in 1975 and 1991 were also microfilaraemic in 2001. Being found microfilaraemic in the first survey was a highly significant risk factor for being found microfilaraemic in the subsequent surveys. These observations strongly indicate that re-infection with Wuchereria bancrofti commonly takes place, and that, compared with an individual who has never been infected, an individual who has been infected in the past has a much higher chance of acquiring a new, detectable infection. As most of the re-identified individuals who were amicrofilaraemic in 2001 but microfilaraemic in one or both of the earlier surveys were still positive for circulating filarial antigens in 2001, it seems that, once an infection has been acquired, the chance of ever becoming free of infection is small. No relationship between past microfilaraemia and the development of chronic filariasis was observed but the number of clinical cases seen in 2001, among the re-identified individuals, was low. The significance of these findings to our understanding of the natural history of W. bancrofti infection is discussed.

Human Bancroftian filariasis: loss of patent microfilaraemia is not associated with production of antibodies to microfilarial sheath.

Antisheath antibodies have been incriminated in elimination of circulating microfilariae in human filariasis since a very significant inverse association has been consistently demonstrated between the two parameters. An attempt was made in the present study to seek empirical proof for the above proposal. Two cohorts of 43 and 73 microfilariae (mf) carriers were examined after 13 and 10 years, respectively, for mf as well as antisheath antibodies. The first cohort was also examined for the presence of circulating filarial antigen (CFA). Of the 43 mf carriers examined after 13 years, 62.8% were free of circulating mf although only 3.7% of them had demonstrable antisheath antibodies. Approximately 93% of this cohort (with or without current microfilaraemia) tested positive for CFA after 13 years indicating continued presence of adult filarial worms in the host after loss of mf in circulation. When the second cohort of 73 mf carriers were examined after 10 years, 30 were found to be amicrofilaraemic and only 6.66% of them had demonstrable antisheath antibodies. We conclude that, in human Bancroftian filariasis, elimination of circulating microfilariae may not be mediated by antibodies to microfilarial sheath.

Protective immunity in human Bancroftian filariasis: inverse relationship between antibodies to microfilarial sheath and circulating filarial antigens.

The existence and the nature of protective immunity in human filariasis continues to be a subject of intense debate. While there is no broad consensus on functional immunity against larval and adult stage parasites, anti-microfilarial immunity has been demonstrated to be mediated by antibodies to the microfilarial sheath. In the present study, circulating filarial antigens (CFA), a marker of active filarial infection in human Bancroftian filariasis, was found to be inversely associated with antibodies to microfilarial sheath in a cohort of 411 subjects representing all categories of filariasis across the clinical spectrum of the disease. Approximately 80% of humans of all age groups (5-65 years) were found to have either CFA or anti-sheath antibodies. The inverse relationship observed between these two parameters was found to be independent of the clinical manifestation; both symptomatic and asymptomatic cases were found to display similar inverse association between CFA and anti-sheath antibodies. The prevalence of anti-sheath antibodies in the paediatric group was found to be very high as compared to adults; 78% of children below the age of 10 years tested positive for anti-sheath antibodies although the mf rate and CFA rate were only 4.5% and 22.7%, respectively, in this age group, indicating that developing larvae or juvenile adult stage parasites could have been the source of antigenic stimulus for induction of antibodies to the microfilarial sheath.

Biased TCR Repertoire in Infiltrating Lesional T Cells in Human Bancroftian Filariasis

To investigate the hypothesis that T cells recognizing specific Ags localize to the site of disease activity in human bancroftian filariasis, we have compared the repertoire of TCR Vbeta gene segments in lesions vs blood in individual patients by RT-PCR ELISA. Vbeta14 and Vbeta24 were overrepresented (5% greater in tissue compared with PBMCs and/or tissue/PBMC ratios in the highest 5% of all tissue/PBMC ratios for all Vbetas for all subjects) in 50% and 40% of study subjects, respectively. Overrepresentation of these two Vbetas did not occur in any control subject. In comparing three patient groups, the proportion of individuals meeting at least one criterion for Vbeta14 overrepresentation was shown to increase in tandem with our current concepts of disease progression (asymptomatic filariasis = 25%; clinical filariasis with active infection = 60%; clinical filariasis without active infection = 71%). In 6 of the 10 individuals with Vbeta14 overrepresentation, Vbeta14 represented >20% of the entire lesional Vbeta repertoire. All but one of the 20 study subjects had at least one Vbeta gene segment that was overrepresented in tissue compared with PBMCs. Only a small number of Vbetas, usually three or less, were overrepresented in any single filariasis patient. However, in the same tissue, no differences between patient groups were found when IFN-gamma, TNF-alpha, IL-4, IL-5, and IL-12 mRNA expression were examined. Taken together, these findings suggest that, in principle, in essentially all patients, whether with subclinical or with clinical filariasis, distinct and limited T cell populations are concentrated in affected tissue.

A role for tumour necrosis factor-alpha in acute lymphatic filariasis.

A spectrum of clinical manifestations is a feature of human lymphatic filariasis. The acute disease is characterized by periodic and self limiting episodes of adenolymphangitis, fever and associated constitutional symptoms, while the chronic disease includes long lasting manifestations such as lymphoedema and/or hydrocoele. The microfilariae carriers are generally free of clinical symptoms. In the present study circulating Tumour Necrosis Factor (TNF-alpha) was measured in human bancroftian filariasis with different clinical manifestations. Significantly elevated levels were observed only in patients with acute disease and not in microfilariae carriers or in patients with chronic manifestations. A detailed analysis of the acute cases indicated an absence of correlation between TNF-alpha levels and duration of the episodes. However, a significant positive correlation was observed between the severity of the disease and the TNF-alpha levels. About 85% of the acute cases with severe manifestations showed raised levels of TNF-alpha while only 6.5% of mild cases showed such levels. Manifestation of fever was also significantly associated with higher levels of TNF-alpha-while 80% of acute cases with fever had significant levels only 24% of acute cases without fever had high levels of TNF-alpha. Based on these observations we propose a mediatory role for TNF-alpha in acute filariasis and the possible use of TNF-alpha inhibitors for clinical management of the disease.

Live Adult Worms Detected by Ultrasonography in Human Bancroftian Filariasis

Ultrasonographic examination of the scrotal area was performed in 14 asymptomatic individuals with bancroftian filariasis and microfilaremia. While in seven subjects (50%) the ultrasonographic findings were normal, lymphatic dilation and tortuosity were observed in the other seven. In these vessels, structures with peculiar aleatory movements (filaria dance sign) were detected. A segment of the lymphatic tract containing these mobile intraluminal structures that was resected surgically from the left spermatic cord of one individual confirmed that these structures were living Wuchereria bancrofti adult worms (two females and one male). Our study demonstrates for the first time the feasibility of using a low-cost, widely available, noninvasive technique (ultrasonography) to detect and monitor living adult worms and lymphatic dilation in patients with bancroftian filariasis.