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. 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.

Onchocerciasis in Guatemala. II. Microfilariae in urine, blood, and sputum after diethylcarbamazine.

Guatermalan volunteers with onchocerciasis were given a dose of diethylcarbamazine to learn if this caused migration of microfilariae of Onchocerca volvulus into urine, blood, and sputum. In 5 of the 10 volunteers, the num0ers of microfilariae in the urine increased considerably following the drug. In the same 5, relatively large numbers of microfilariae were observed in the blood and sputum specimens. Response in the remaining 5 was negligible. Four controls given a placebo did not respond. Interestingly, however, 2 control subjects had onchocercal microfilariae in their concentrated blood specimens and 3 control subjects had microfilariae in the sputum. Therefore, we believe that microfilariae, if searched for, may be found in other parts of the patient not normally associated with the infection.

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.