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.

Some observations on complement fixation in onchocerciasis in Guatemalans.

Recent investigations of infections with Onchocerca volvulus in Guatemala presented the opportunity to study some aspects of complement fixation (CF) antibody titers. An extract of adult O. volvulus obtained from nodules excised from patients was used as antigen. Serum was procured from individuals whose intensity of infection was determined by skin snip counts of microfilariae. In general there was an inverse relationship between intensity of infection and CF titers. This correlation was significant in men 40 years and older. The CF titer of women was greater than that of men with the same intensity of infection.

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.

Daytime variation in the density of Onchocerca volvulus microfilariae in human skin.

One aim of this study was to determine whether a corneal-scleral punch biopsy instrument provides skin specimens of sufficiently uniform size so as to eliminate the need to weigh or measure the specimens in order to provide a reproducible index of the density of Onchocerca volvulus microfilariae in the skin. A second aim was to determine whether the density of microfilariae in the skin varies with the time of day. The reports of others on the latter are contradictory. Duplicate skin specimens were taken from 10 people four times during one day with a corneal-scleral punch biopsy instrument. Each specimen was weighed and measured, and the number of microfilariae were counted. Although the specimens were not of uniform weight or surface area, the number of microfilariae per specimen was as good an index of the density of larvae in the skin as the number of microfilariae per mg, or per mm(2) of skin. This may not be true when other methods of procuring skin specimens are utilized. A universally acceptable standard method is advocated. The density of microfilariae in the skin approximately doubled from morning to midday, and began to decline by early evening.