Parasitological, serological, and clinical studies of Wuchereria bancrofti in Limbe, Haiti

Wuchereria bancrofti infection in Haitian immigrants and the risk of re-emergence of lymphatic filariasis in the Brazilian Amazon

INTRODUCTION:

Lymphatic filariasis (LF) is a public health problem in Haiti. Thus, the emigration of Haitians to Brazil is worrisome because of the risk for LF re-emergence.

METHODS:

Blood samples of Haitian immigrants, aged ≥18 years, who emigrated to Manaus (Brazilian Amazon), were examined using thick blood smears, membrane blood filtration, and immunochromatography.

RESULTS:

Of the 244 immigrants evaluated, 1 (0.4%) tested positive for W. bancrofti; 11.5% reported as having received LF treatment in Haiti.

CONCLUSIONS:

The re-emergence of LF in Manaus is unlikely, due to its low prevalence and low density of microfilaremia among the assessed Haitian immigrants.

Spatial clustering of filarial transmission before and after a Mass Drug Administration in a setting of low infection prevalence

BACKGROUND: In the global program for the elimination of lymphatic filariasis (LF) longitudinal assessment of the prevalence of microfilaremia and antigenemia is recommended to monitor the effect of mass treatment on transmission. Additional monitoring tools such as entomologic and antibody methods may be useful in identifying residual foci of infection. In this study, we characterized serologic markers of infection and exposure spatially both before and after mass treatment, in an area of initial low Wuchereria bancrofti infection prevalence. METHODS: Consenting persons in the sentinel community were tested for circulating microfilaria and antigen (by immunochromatographic test) before and after the 1st annual mass drug administration of diethylcarbamazine and albendazole. A cohort of 161 persons provided serum specimens both years that were tested for antifilarial IgG (1 and 4) antibody. Every house was mapped using a differential Global Positioning System; this information was linked to the serologic data. W. bancrofti infection in the mosquito vector was assessed with year-round collection. Multiple linear regression was used to investigate the influence of antigen-positive persons on the antifilarial antibody responses of antigen-negative neighbors. RESULTS: After mass treatment, decreases were observed in the sentinel site in the overall prevalence of antigen (10.4% to 6.3%) and microfilaremia (0.9 to 0.4%). Of the persons in the cohort that provided serum specimens both years, 79% received treatment. Antigen prevalence decreased from 15.0% to 8.7%. Among 126 persons who received treatment, antigen and antifilarial IgG1 prevalence decreased significantly (p = 0.002 and 0.001, respectively). Among 34 persons who did not receive treatment, antifilarial IgG1 prevalence increased significantly (p = 0.003). Average antifilarial IgG1 levels decreased in households with high treatment coverage and increased in households that refused treatment. Each 10-meter increase in distance from the residence of a person who was antigen-positive in 2000 was associated a 4.68 unit decrease in antifilarial IgG1 level in 2001, controlling for other factors (p = 0.04). DISCUSSION: Antifilarial antibody assays can be used as a measure of filarial exposure. Our results suggest that micro-scale spatial heterogeneity exists in LF exposure and infection. Treatment appeared to be associated with reduced exposure at the sub-community level, suggesting the need to achieve high and homogeneous coverage. Public health messages should note the benefits of having one's neighbors receive treatment with antifilarial drugs.

Prevalence of diurnally subperiodic bancroftian filariasis among the Nicobarese in Andaman and Nicobar Islands, India: effect of age and gender

We conducted a cross-sectional survey to assess the prevalence of disease and microfilaraemia caused by diurnally subperiodic strain of Wuchereria bancrofti transmitted by day biting Aedes niveus in Teressa Island, remotely located in the Nicobar district of Andaman and Nicobar Islands. Lymphatic filariasis is a considerable public health problem on this island with an overall endemicity rate of 16.2%. There was a gradual increase in microfilaraemia prevalence with age, reaching a plateau above 30 years. Both the microfilaraemia and disease rates were significantly higher in males (14.7% and 5.2%) than females (8.6% and 1.5%, P < 0.001). The age and gender specific distribution of chronic manifestations show a gradual increase with age, whereas acute disease started to occur from age 40 in males. Hydrocele (84.6%) was the commonest disease manifestation among males, whereas lymphoedema was the only manifestation encountered among females. As vector control measures are not practicable in this setting, chemotherapy using diethylcarbamazine (DEC) is the only potential option to control this disease.

Filariose bancroftiana em áreas urbanas do Estado de Alagoas, nordeste do Brasil: estudo em população geral

Com objetivo de estudar a situação da filariose linfática em Alagoas, foi realizado um inquérito hemoscópico na população geral de áreas urbanas das três diferentes regiões fisiográficas do estado. Dos 101 municípios, foram pesquisados aleatoriamente 10, sendo a bancroftose detectada somente na capital, Maceió. Em um estudo seccional feito com a população geral de 4 bairros desta cidade foram examinados 10.973 indivíduos sendo detectados 226 microfilarêmicos, com prevalências nos bairros variando de 0 a 5,4%. Tanto a prevalência de microfilarêmicos como a microfilaremia média foram significativamente maiores em indivíduos do sexo masculino. Entre os examinados não nascidos em Maceió, o tempo de residência na área endêmica foi significativamente maior entre microfilarêmicos que entre amicrofilarêmicos. Baseado nestes dados, medidas de controle já foram implementadas visando a eliminação da filariose linfática na região.

Epidemiology of acute filarial episodes caused by Wuchereria bancrofti infection in two rural villages in Tamil, Nadu, south India

This year-long study investigated the epidemiology of acute filarial episodes due to Wuchereria bancrofti in 2 rural villages in south India. The annual incidence of 96.5 episodes/1000 population was significantly higher in males (108.5) than females (84.1) an strongly age dependent. First occurrence of acute disease was observed in 0.86% of the population, and the average duration of each episode was 3.6 +/- 2.0 d. Although more than half (63.5%) of the affected individuals suffered only 1 episode, a few experienced as many as 8 over the one-year period. Individuals with chronic disease were more prone to acute attacks, with 82.9% of the total episodes occurring in this group. No seasonal pattern was observed in the frequency of episodes. Probit analysis showed that the number of episodes per affected person was dependent on sex and chronic condition. Swelling of lymph nodes in the inguinal region and fever were the most common symptoms of acute disease. The high incidence and resulting debility observed in this study suggest that acute episodes are a significant health problem associated with lymphatic filariasis. There is clearly a need for more studies on this acute form of filarial disease to aid the understanding of the aetiology and epidemiology of acute episodes, in planning appropriate control interventions, and in evaluating the resulting health burden.

Re-assessing the global prevalence and distribution of lymphatic filariasis

This paper estimates the global burden of lymphatic filariasis based on a review of the published literature on infection and disease surveys. A method for aggregating and projecting prevalence data from individual studies to national, regional and global levels, which also facilitates the estimation of gender and age-specific burdens, is presented. The method weights in favour of the larger, and hence presumbably more reliable, studies and relies on estimated empirical relationships between gender, age, infection and disease in order to correct studies with incomplete data. The results presented here suggest that although the overall prevalence of filariasis cases is 2.0% globally (approximately totalling 119 million cases), the disease continues to be of considerable local importance, particularly in India and Sub-Saharan Africa. Estimates by age and gender clearly show that, unlike other helminth infections, filariasis is mainly a disease of the adult and older age-classes and appears to be more prevalent in males. This work suggests that the derivation of more accurate estimates of the burden of filariasis will require a better understanding of both the epidemiology and the spatial aspects of infection and disease. It also suggests that filariasis is preventable based on a geographically targeted strategy for control.

Clinical epidemiology of bancroftian filariasis: effect of age and gender

A cross-sectional survey was used to determine the prevalence of disease (n = 6493) and microfilaraemia (n = 24,946) due to Wuchereria bancrofti in Pondicherry, south India. The total disease attributable to filariasis was significantly higher in males (13.67%) than females (2.26%), due to the occurrence of hydrocele in males. While the prevalence of chronic signs was clearly age-dependent in both sexes, that of acute signs was independent of age. Thus the age and gender structure of the survey sample will crucially influence apparent prevalence. Examination of the gender differences in the point prevalence of disease in 12 areas of India showed a significant relationship between occurrence of disease and gender, but this relationship did not significantly differ between northern and southern Indian populations. The study suggested that the failure to appreciate the importance of age and gender in disease prevalence has led to misconception about disease patterns in India.

Sex differentials in susceptibility to lymphatic filariasis and implications for maternal child immunity

This paper reviews epidemiological data to see if there are sex differentials in prevalence, density and clinical pathology due to lymphatic filariasis. Of 53 studies from Africa, South East Asia, the Indian Subcontinent and The Americas, 43 showed a lower mean prevalence of infection in females than in males. Prevalence is consistently lower in women of reproductive age and this is statistically significant in 16 of 32 studies classified by age and sex. Density of infection is also lower in the reproductive age but may be higher in children and in older women. Clinical disease is also lower in women and pathology has a later age of onset and rise to peak prevalence than in males. The paper assesses the evidence that lower rates of infection and clinical pathology are due to less exposure of females to infective vectors. It seems unlikely that exposure alone could account for these differences which are observed for both bancroftian and brugian filariasis, irrespective of periodicity. Several investigators have suggested that females have increased resistance to infection and this is supported by serological studies showing high antibody positivity to adult worm antigens in females. The review concludes that the association with the reproductive years suggests a pregnancy-associated mechanism. This has important implications for maternal-fetal interactions and maternal filarial infection may influence the development of immunity in children.

Microfilaraemia, serum antibody and development of clinical disease in microfilaraemic subjects infected with Wuchereria bancrofti and treated with diethylcarbamazine citrate

A seroepidemiological survey of bancroftian filariasis was carried out in 2 townships in Sri Lanka with the objectives of determining the microfilaraemia rates, dependence on age and sex, susceptibility to re-infection, effect of diethylcarbamazine therapy on serum antibodies to microfilarial surface antigens, and the predictive value of the indirect fluorescent antibody test. The mean microfilaraemia rate was 5.4%. Microfilaraemia was not sex-dependent but a marginally elevated incidence was seen in the 6-35 year age groups. In up to 58% of the microfilaraemic patients who had been treated for microfilaraemia previously, a second phase of microfilaraemia was seen 2-7 years after treatment. This was unlikely to have been due to incomplete parasite elimination. Antibodies to microfilarial surface were found in 24-35% of microfilaraemic patients and in 14-63% of amicrofilaraemic symptomatic subjects. Serum anti-microfilarial surface antibody levels did not alter with chemotherapy with diethylcarbamazine citrate. The findings of follow-up investigations of microfilaraemic subjects were compatible with the notion that microfilaraemia does not necessarily lead to clinical disease.

Epidemiology of Wuchereria bancrofti in Leogane, Haiti

A survey for Wuchereria bancrofti in Leogane, Haiti, revealed that 140 of 421 individuals (33%) had a patent infection, of which 40% lived in the suburban outskirts of the city. The median microfilaria density was 19.1 per 20 mm3 of blood for suburban dwellers compared with only 8.8 for those living in the city. The vector, Culex quinquefasciatus (Say), breeds mostly in and around numerous rum distilleries, located exclusively around the periphery of the city, and this undoubtedly accounts for the higher prevalence and intensity of infection among suburban dwellers.