Efficient assessment of filariasis endemicity by screening for filarial antigenaemia in a sentinel population.

We have previously reported that a monoclonal antibody-based antigen detection assay (AD12) is sensitive and specific for Bancroftian filariasis in Egypt. The purpose of the present study was to demonstrate the use of this assay in a sentinel population as a means of efficiently screening for filariasis endemicity. Antigen testing was performed with finger-prick blood collected during the day from 743 schoolchildren (ages 11-16 years). The school draws students from 5 villages in Qalubia Governorate, 35 km north-east of Cairo, Egypt. The prevalence of filarial antigenaemia in the school was 17.2%. Antigenaemia rates in children from the 5 villages were 29, 20, 18, 17, and 10% (non-uniformity significant by chi 2 analysis, P = 0.02). These data agree with Ministry of Health rankings of relative endemicity for these villages based on prior night blood surveys. The village with the highest antigen prevalence in children was surveyed one year before the present study. Prevalence rates of antigenaemia and microfilaraemia at that time for a different sample of children aged 11-16 years were 33% and 22%, respectively. We conclude that antigen detection in schoolchildren of this age group is an efficient means of assessing filariasis endemicity in Egypt.

Community diagnosis of Bancroftian filariasis.

The objective of this study was to find the best tests for efficiently estimating the true prevalence of Bancroftian filariasis in endemic areas. The study population comprised 427 people over 10 years of age in an endemic village in Egypt. Four tests were evaluated; a standardized clinical examination, night blood examinations for microfilariae (50 microL thick films and 1 mL membrane filtration), and a test for circulating filarial antigen. 191 subjects (44.75%) had at least one positive test and were considered to have filariasis. The sensitivities of clinical examination, thick films, membrane filtration and antigen testing for filariasis were 16%, 50%, 64%, and 88%, respectively. Relative to membrane filtration of night blood, the filarial antigen test had a sensitivity of 97.5%, a positive predictive power of 71%, and a negative predictive power of 99%. None of the blood tests was a sensitive indicator of clinical filariasis; 69% of clinical cases were negative in all 3 blood tests and would have been missed if clinical examinations had not been done. Therefore, we recommend a combination of clinical examination and the filarial antigen test (with optional examination for microfilariae of those with positive antigen tests) for community diagnosis of Bancroftian filariasis in endemic areas.

The resurgence of lymphatic filariasis in the Nile delta.

A study of 325,000 residents of 314 villages in six governorates of the Nile delta area of Egypt revealed that the prevalence of lymphatic filariasis increased from < 1% in 1965 to > 20% in 1991, especially in the governorates of Qalyubiya, Monufiya, Dakhaliya, and Giza. The distribution of the communites with endemic filariasis is focal. Clusters of villages with high prevalences are surrounded by others in which the disease is absent, although their environmental, social, and agricultural features appear similar. The article analyses why the significant decline in filariasis between 1945 and 1965 in Egypt has been followed by a resurgence of the disease.

Regional differences of agromedical problems : I. Agromedical problems in humid tropical areas ; II. The public health perspective ; III. Persistence of chemicals

This chapter outlines features of the tropical region as they relate to pesticide protection. Three major areas are examined : public health diseases, geographical factors influencing chemical persistence and geographical impacts on agromedicine. The need is emphasized for tropical countries to develop relevant intermediate technology and an infrastructure which would allow the increasing quantities of pesticides in the region to be used with maximun human and environmental safety. The implications of this increased use of pesticides in the tropics are discussed in this chapter. Reference will be made to the actual or potential effects of pesticide use on human and environmental health in the area. Focus will be directed on possible solutions for problems which have been identified (AU)

Sowda--onchocerciasis in north Yemen: a clinicopathologic study of 18 patients.

Sowda is an unusual form of onchocerciasis in Yemenites that differs from African onchocerciasis. Clinical and pathological studies were performed on 18 patients in Yemen Arab Republic (North Yemen). Biopsies of skin and lymph nodes were taken, and then processed at the Armed Forces Institute of Pathology, Washington, D.C. The most striking clinical features were swollen, darkened, pruritic, papular skin changes that were usually limited to one leg, more rarely to one arm, and large soft regional lymph nodes. Dermal changes were deeper and more diffuse than in African onchocerciasis, with many large fibroblasts and plasma cells. Microfilariae of Onchocerca volvulus were much rarer in skin from Yemenites with sowda. When patients were treated with diethylcarbamazine, the dermatitis became suddenly worse as the microfilariae degenerated and provoked acute inflammation. The dermatitis decreased after several days of treatment. Enlarged lymph nodes from sowda have shown follicular hyperplasia, in contrast to follicular atrophy and perivascular fibrosis that are characteristic of lymph nodes from cases of African onchocerciasis. Cell-mediated and humoral immunity may be more active in sowda than in African onchocerciasis.

Epidemiology of poly-parasitism. IV. Combined effects on the state of health.

The assessment of morbidity caused by chronic parasitic infections in the populations of endemic areas has remained difficult and controversial. Contributing to this predicament is the frequent occurrence of multiple infections with agents that can cause a wide range of clinical manifestations, from the frequent symptomless carrier state to overt disease with more or less specific clinical manifestations. In the interpretation of the complex morbidity patterns found in rural populations of tropical countries, it is often difficult to make a clear determination of cause and effect. The situations is further complicated by the low degree of pathognomicity of the clinical manifestations of even the advanced stages of certain parasitic diseases. The paper gives examples that illustrate the interaction between endemic malaria and schistosomiasis as important causes of hepatosplenomegaly. Also shown in the paper are the inter-relationships between the nutritional status and the number of multiple infections with parasites found in African villages as well as the association between habitual coca leaf chewing, malnutrition and hookworm disease in a Peruvian community of mixed ethnic origin. The paper describes micro-epidemiological features of poly-parasitism by comparing the prevalence and intensity of infection with Onchocerca volvulus, Schistosoma mansoni and S; haematobium between sub-groups in the village population who have different sources of domestic water supply. In two African villages with endemic schistosomiasis where mass treatment will be administered, only 25% of the residents with parasitologically confirmed S. haematobium infection and 12% of those with S. mansoni had single infection; the remaining majority had at least one additional patent parasitic infection of public health importance.

Epidemiology of poly-parasitism. II. Types of combinations, relative frequency and associations of multiple infections.

Frequency distributions, including all of the observed types of combinations of multiple infections with different helminths and protozoa are presented for sample villages of the African Savannah and of the trans-Andean part of Peru. Measurements of correlation between these infections based on properties of the multivariate, multinomial distribution are calculated to show age and sex patterns of association in different population samples. A correlation matrix for combined infections with Dipetalonema perstans, D. streptocerca and Loa loa, in villages in the rain forest of Zaire indicates that there is a statistically significant association between the two species of Dipetalonema and L. loa. There is also a strong association between the numbers of the microfilariae of D. perstans and D. streptocerca in multiply infected individuals. This correlation is strong only in the rain forest; it is insignificant in the other ecological zones of Bas-Zaire included in the study. The data suggest that there may be selective host factors that influence the extent, distribution and the types of multiple infections in a community.

Epidemiology of poly-parasitism. III. Effects on the diagnostic capacity of immunological tests.

The paper describes some effects of interaction between different types of parasitic infections on the diagnostic capacity of immunological tests for parasitic diseases. Examples shown include an analysis of association for anergy to tuberculin in skin tests of individuals with and without skin manifestations of onchocerciasis; skin tests with P. westermani and C. sinensis antigens to detect double infections in patients harbouring both trematodes; geographical evaluation of the sensitivity of the complement fixation (CF) test for schistosomiasis with S. mansoni antigen between different communities in Chad; reduced sensitivity of the CF test for schistosomiasis in patients with confirmed schistosomiasis who have also onchocerciasis; studies on the specificity of the slide flocculation (SF) test for schistosomiasis in relation to specified intestinal parasites and to the presence of antibodies to E. granulosus and T. spiralis in villages of Afghanistan; and a study of association between poly-parasitism and anticomplementary activity in the sera of population samples from the African Savannah. The combined investigations indicate that there are large dissimilarities in test performance between communities with different disease spectra and nutritional status. The findings suggest that polyparasitism interferes with immunodiagnostic tests both directly through cross-reactions with antigens and antibodies and indirectly through its effects on nutrition and on mechanisms affecting the complement system. Large scale screening for parasitic diseases with immunodiagnostic tests in areas in which the medical problems are not well-known should be prededed by a small, well-planned pilot study in which the relative sensitivity and specificity of the test can be determined before its use in extensive population studies.

Epidemiology of poly-parasitism. I. Occurrence, frequency and distribution of multiple infections in rural communities in Chad, Peru, Afghanistan, and Zaire.

Parasitic diseases are predominantly rural diseases. They are often associated with poverty, illiteracy, poor sanitation and high risks of exposure to environmental and biological hazards. Because these factors are also essential determinants in the epidemiology of a variety of other infections with quite different etiologies, occurrence of multiple infections in the same people is common. In the tropics, polyparasitism may involve diseases of major public health inportance such as malaria, schistosomiasis, filarial infections, trypanosomiasis, and others. The paper presents data on the frequency and types of multiple infections with different parasitic and other infectious agents for thirteen villages of Chad, Peru and Afghanistan. The age and sex patterns of a number of observed combinations of parasitic and other diseases are shown for different ecological zones. Concomitant infections with up to five species of filarial worms are found in residents of villages in the Congo River Basin of Zaire. The specific types of combinations of these infections vary from place to place and appear to be closely linked to ecological factors.

Onchocercal dermatitis: ultrastructural studies of microfilariae and host tissues, before and after treatment with diethylcarbamazine (Hetrazan).

Specimens of skin from four Cameroon patients with severe onchocercal dermatitis, before and after treatment with diethylcarbamazine (DEC), were studied by light and electron microscopy. Microfilariae of Onchocerca volvulus have ultrastructural features resembling those of microfilariae of other genera. Between the surface layer of the cuticle and the trilaminate membrane, there is an electrolucent zone which is much wider in degenerating microfilariae than in intact microfilariae. Widening of the zone may result from DEC-induced release of component(s) of the cuticle, possibly collagen or mucopolysaccharide. Between the cuticle and dermal collagen there are granular deposits which might be immune complexes involving the collagenous component of cuticle. Others have shown that DEC does not kill microfilariae in vitro. Treatment with DEC presumably "unmasks" microfilariae in the skin so that they are recognized as foreign bodies and are destroyed by the host's defenses. Histiocytes and eosinophils are seen in close proximity to degenerating microfilariae. Enzymes from histiocytes and eosinophils might readily penetrate the cuticle altered by DEC treatment, and digest various components within the microfilariae. Alternatively, the widening of the electrolucent zone might result directly from the action of leucocytic or histiocytic enzymes, after the microfilaria has been killed by other mechanisms.

Onchocerciasis in Guatemala. I. Epidermiological studies of microfilaruria.

Microfilariae of Onchocerca volvulus were detected in the urine of 65 residents of three coffee plantations near Yepocapa, Guatemala. In this area the prevalence of microfilaruria is estimated to be between 17% and 30% of the population 10 years of age and older. Almost all of the people examined had clinical manifestations of onchocerciasis and 80% of them had microfilariae in skin snips. The frequency of microfilaruria is associated with the number of microfilariae in the skin. Within each age group those who had lived longer on the coffee plantations were more likely to have microfilariae in a skin snip and more likely to have microfilariae in their urine. The presence of subcutaneous nodules or history of prior nodulectomy did not reduce the incidence of microfilaruria nor did the presence of subcutaneous nodules increase the incidence of microfilariae in the urine.

Onchocerciasis in Guatemala. III. Daytime periodicity of microfilariae in skin.

Periodicity of microfilariae of Onchocerca volvulus in the skin was not believed to exist until investigators in Africa recently demonstrated diurnal periodicity. Interestingly, this maximal density of microfilariae in the skin has been shown to coincide with the peak biting time of the Simulium vector. The current study was performed as part of other studies in Guatemala. Maximal density of microfilariae in the skin was at 1000 hours or shortly therafter. This peak is earlier than reported in Africa. The most active feeding period of Simulium ochraceum, believed to be the principal vector in Guatemala, had been previously shown to be from 0800 to 1000 hours. The current report lends support to other findings indicating that Onchocerca volvulus microlilariae have a diurnal periodicity. In addition, the occurrence of peak vector biting time at the same time as maximal numbers of microfilariae in the skin strengthens a hypothesis that these synchronous cycles have a biological significance.

Onchocerciasis: prevalence of microfilaruria and other manifestations in village of Cameroon.

Onchoecercal microfilaruia was studied in the course of an epidemiologic investigation of diseases, infections, and general health conditions in a rural village on the Adamaoua Plateau in northern Cameroon. Microfilariae of Onchocerca volvulus were observed in nearly one half of the skin snips taken from the village residents. The prevalence of onchocerciasis as diagnosed from skin snips increased with age, and was greater for males than females. The number of microfilariae per skin snip also increased wth age. The presence of subcutaneous nodules, inguinal lymphadenopathy, microfilariae in the urine, ocular lesions and prolonged itching all were related to both age and the presence of microfilariae in skin biopsy specimen, as well as to intensity of infection. Microfilaruria was not restricted to individuals with severe onchocerciasis.