Prevalence Of Lymphatic Filariasis Research Articles

A geostatistical analysis of the geographic distribution of lymphatic filariasis prevalence in southern India.

Gaining a better understanding of the spatial population structure of infectious agents is increasingly recognized as being key to their more effective mapping and to improving knowledge of their overall population dynamics and control. Here, we investigate the spatial structure of bancroftian filariasis distribution using geostatistical methods in an endemic region in Southern India. Analysis of a parasite antigenemia prevalence dataset assembled by sampling 79 villages selected using a World Health Organization (WHO) proposed 25 x 25 km grid sampling procedure in a 225 x 225 km area within this region was compared with that of a corresponding microfilaraemia prevalence dataset assembled by sampling 119 randomly selected villages from a smaller subregion located within the main study area. A major finding from the analysis was that once large-scale spatial trends were removed, the antigenemia data did not show evidence for the existence of any small-scale dependency at the study sampling interval of 25 km. By contrast, analysis of the randomly sampled microfilaraemia data indicated strong spatial contagion in prevalence up to a distance of approximately 6.6 kms, suggesting the likely existence of small spatial patches or foci of transmission in the study area occurring below the sampling scale used for sampling the antigenemia data. While this could indicate differences in parasite spatial population dynamics based on antigenemia versus microfilaraemia data, the result may also suggest that the WHO recommended 25 x 25 km sampling grid for rapid filariasis mapping could have been too coarse a scale to capture and describe the likely local variation in filariasis infection in this endemic location and highlights the need for caution when applying uniform sampling schemes in diverse endemic regions for investigating the spatial pattern of this parasitic infection. The present results, on the other hand, imply that both small-scale spatial processes and large-scale factors may characterize the observed distribution of filariasis in the study region. Our preliminary analysis of a mountain range associated large-scale trend in the antigenemia data suggested that a nonlinear relationship of infection prevalence with elevation might be a factor behind such observed global spatial patterns. We conclude that geostatistic methods can provide a powerful framework for carrying out the empirical investigation and analysis of parasite spatial population structure. This study shows that their successful application, however, will crucially depend on our gaining a more thorough understanding of the appropriate geographic scales at which spatial studies should be carried out.

Developments in lymphatic filariasis research

Lymphatic Filariasisedited by T.B. Nutman, Imperial College Press, 2000. £30.00 (283 pages) ISBN 1 86094 059 5The book Lymphatic Filariasis is part of the series Tropical Medicine: Science and Practice edited by G. Pasvol and S.L. Hoffman. Lymphatic Filariasis is a comprehensive book, which consists of ten chapters written by 13 internationally well recognized scientists working in the field of lymphatic filariasis. Emphasis is on clinical and laboratory diagnosis, immunology in addition to treatment and control. This book is particularly helpful for readers who are medically oriented, and is recommended for graduate students and scientists involved in teaching and research of parasitic diseases. Many new developments in lymphatic filariasis research, especially recent insights in lymphatic pathology and the new strategies for treatment are summarized in this book. Hence, it is a must have for those working or involved in filariasis control programmes. This book covers almost all aspects of lymphatic filariasis, except for entomology and ecology of the infection. The editor mentioned in the preface that dramatic advances have been made during recent years. Therefore, frequent revisions will be needed to include the current research progress. With a lymphatic filariasis elimination programme under way, which aims to eliminate lymphatic filariasis as a public health problem by the year 2020, such updates will be essential to reflect the future status of lymphatic filariasis.Minor points to be criticized include the repetitions between the chapters: for example, four chapters mention the estimated prevalence of lymphatic filariasis (128 million cases) in their first paragraphs. Lymphatic filariasis is caused by three different filarial species, therefore the morphological description for each developmental stage should pay more attention on the examined species. Furthermore, different strains of Brugia malayi have been described, which differ in their degree of anthropophily, their periodicity and their mosquito vectors, and only few of these strains can be maintained for several generations in laboratory rodents. Some statements appear contradictory and need clarification. For example, it is cited that, ‘in bancroftian filariasis, recurrent attacks of fever associated with lymphadenitis are less frequently seen as in brugian filariasis,’ whereas four pages further, it is stated that, ‘the frequency of acute attacks is generally higher in bancroftian filariasis as compared to brugian filariasis’. In the chapter on the diagnosis, it should be noted that microfilariae of Brugia timori are significantly longer than those of B. malayi and cannot, therefore, be summarised within one group. Although not recommended for routine treatment of filariasis, it should be mentioned that the use of antibiotics to target the Wolbachia endobacteria in filarial parasites could be a promising new strategy for chemotherapy. The observation that worms and microorganisms can cause lymphatic disease is probably a new and noteworthy issue for some readers. However, most underlying studies have been performed on Wuchereria bancrofti and need to be confirmed for Brugia. One important tool to study is the localisation of adult worms in humans by ultrasound, which, so far, has only been reported for W. bancrofti. The authors describe, ‘fundamental differences in the pathogenesis of lymphoedema and hydroceles’. Because no hydroceles are found in brugian filariasis, the authors should stress that also differences in the pathogenesis of bancroftian and brugian filariasis have to be postulated.The form and the layout of the book are good, but it contains only a few colour images of low quality. Apart from a few gaps in biological aspects of the infection and some minor inaccuracies, the book gives a comprehensive overview of lymphatic filariasis.

Hydrocelectomy: a proxy for hydrocele prevalence in coastal Kenya.

To assess the value of hydrocelectomy as an indicator of the prevalence of lymphatic filariasis, the frequency of hydrocelectomy was investigated in five hospitals in an area of coastal Kenya where filariasis is endemic. Two of the hospitals studied (Kinango and Msambweni) were in Kwale district, two (Kilifi and Malindi) in Kilifi district and one (the Coast Provincial General Hospital) in Mombasa. Surgical operations performed between January 1991 and August 1993 were tallied from the main theatre registers. Additionally, admission files for hydrocelectomy patients were examined prospectively between September 1993 and February 1994, to obtain age profiles. Hydrocelectomies accounted for 27.6%, 16.6%, 13.6%, 4.3% and 2.0% of the major operations (totalling 6339) recorded in Kinango, Msambweni, Kilifi, Malindi and Coast Provincial General Hospital, respectively. The proportion of operations involving hydrolectomy was significantly higher in the two hospitals in Kwale district, in the southern part of the study area, than in the two hospitals in Kilifi district, in the northern part (23.4%, with 95% confidence intervals of 20.9%-25.9%, v. 10.3%, with 95% confidence intervals of 8.7%-11.9%; P < 0.001). The generally high frequencies of hydrocelectomy in the study area are evidence of the heavy social and economic burden imposed by hydrocele-attributable morbidity and its management. The age distribution pattern of the hydrocelectomy patients paralleled that of the individuals with hydrocele in the surrounding area.