Search

After an interval of four years the same observers used the same standardized techniques to re-examine 1,016 people in 12 heavily infected rain-forest and savanna villages in Cameroon. The changes in the number of nodules and in the concentration of microfilariae in the skin and eye are described. These latter changes are correlated with the development and/or deterioration of eye lesions and visual impairment. In both the rain-forest and the savanna there was a strong association between the development of eye lesions and a high concentration of microfilariae, not only in the eye but also in the skin, and more so at the shoulder than at the buttock. The importance of these findings for the prevention of blindness is discussed.

The antibody response to group C meningococcal polysaccharide vaccine was studied in a Nigerian village. Household clustering of poor responders to immunization was detected. Age had a marked effect on antibody response, maximal titres being obtained only in those over the age of 10 years. Children with malaria parasitaemia had a lower antibody response than those without parasitaemia and subjects with the genotype AA had a lower antibody response than those with the genotype AS. The antibody response to the vaccine was not influenced by mild degrees of malnutrition but children with clinical marasmus or kwashiorkor were excluded from the study.

Simultaneous xenodiagnosis was made of 29 patients with chronic Chagas's disease, six naturally infected opossums ( Didelphis azarae ) and of a Rhesus monkey with an experimental chronic infection with Trypanosoma (Schizotrypanum) cruzi (Peru strain). Patients and opossums were from an endemic area in the state of Bahia, Brazil, where Panstrongylus megistus is the sole domiciliary vector of the disease to man. Various instars of P. megistus Triatoma infestans and Rhodnius prolixus were used. The proportion of bugs infected was compared with bloodmeal intake by a computer programme using linear logistic analysis. The analysis showed that there are intrinsic interspecific differences in susceptibility to infection with Trypanosoma cruzi between the three triatomine species used and that subsequent infection of bugs with T. cruzi is correlated with the quantity of blood ingested. The results show that interspecific differences of bloodmeal size and intrinsic differences in susceptibility to T. cruzi between triatomine species are limiting factors for the standardization and interpretation of the results of xenodiagnosis.

Age-specific prevalence rates of antibody to O'nyong-nyong virus were determined in samples of the population in the Kano Plain, near Kisumu, and Bunyala. Presented graphically, the rates show a cl...

SUMMARYThis paper describes further characteristics of the immunization of sheep against schistosomes using live, irradiated schistosomula. Sheep immunized with a non-virulent strain of Schistosoma mattheei were protected against a more virulent strain of the same species for over a year. As there was no evidence that the irradiated parasites were able to persist this long, it was concluded that the vaccine had induced a sterile resistance. Heterologous vaccination, using irradiated S. mattheei schistosomula to immunize against S. bovis or irradiated S. mansoni schistosomula to immunize against S. mattheei, failed to induce any protection.

The results of an onchocerciasis survey of total populations aged 5 years and over in 16 heavily infected villages in Cameroon rain-forest and savanna zones are reported. Using standardized parasitological and clinical techniques the same observers examined the intensity of infection and clinical manifestations in 1,098 cases in the rain-forest and compared them with those found in 1,128 cases in the savanna. The following Table summarizes the main findings:- Rainforest Savana Prevalence of nodules 80–90% 60–70% Mean number of nodules per person +++ ++ Microfilarial skin density ++ −++ Skin atrophy ++ +++ Shin depigmentation +++ + Groin lymphadenopathy +++ ++ Hanging groin ++ + Microfilarial invasion of cornea ++ +++ Microfilarial invasion of anterior chmaber +++ +++ Microfilarial invasion of vitreous + ++ Snowflake corneal opacities ++ + Sclerosing keratitis + +++ Iritis + +++ Optic atrophy + + Choroidoretinitis + + Blindness 2.0% 5.1% + =at low level ++ =at medium level +++ at high level It is suggested that the differences between rain-forest and savanna may be due to variations in host response resulting from differences in the intensity and patterns of transmission. Different pathogenicity of the rain-forest and savanna strains of parasite is also considered to be of importance, and it is suggested that concomitant infections may influence the immunological response. Hormonal factors are considered to be important in influencing the differences in the patterns and severity of infections between males and females.

Laboratory observations were made on the transmission of Wuchereria bancrofti by Culex quinquefasciatus and Anopheles gambiae, natural vectors in East Africa, and by Aedes aegypti, an experimental vector. Mosquitoes were fed on human carriers with one to 2,667 microfilariae (mff/ml) of peripheral blood and the numbers of mff ingested were determined. The mosquitoes demonstrated a ‘concentrating effect’ and ingested 8.6 to 12-fold more mff than the expected number based on the density of mff in the carrier and the size of the blood meal. Studies on Culex showed that only 2.7 to 13% of the ingested mff developed into infective larvae (L3s). Emphasis was given to the transmission of Wuchereria from low density carriers with less than 10 mff/ml of peripheral blood—a value that approximates the threshold level of microfilaraemia detectable with conventional diagnostic techniques. By combining our laboratory data with published field data on the biting rates and longevity of mosquitoes in East Africa, we estimate that each low density carrier could serve as a source for nil to 15 L3s/year in Cx quinquefasciatus and 0.3 to 8 L3s/year in An. gambiae depending on the particular community. These estimates are relevant when formulating strategy to control bancroftian filariasis by mass chemotherapy with diethylcarbamazine. Experience with this drug has shown that a proportion of the carriers in a community continue to circulate mff at low levels after treatment. The present data demonstrate that these carriers serve as a reservoir of infection for mosquitoes.

A study of morbidity in Schistosoma mansoni infection was made in 593 Sudanese patients seen in a four-year period in Khartoum Civil Hospital. Clinical and laboratory findings were compared in three egg-count groups and in four clinical forms of the infection. Patients were divided into three levels of intensity of infection: light (up to 100 eggs/gram of stool), moderate (101--400 eggs/g) and heavy (more than 400 eggs/g). According to the presence or absence of visceral enlargement, infected subjects were divided into one of four clinical forms: intestinal, hepatic, hepatosplenic and splenic. Among the symptoms only the passage of blood in the stools was significantly related to intensity of infection, and fever was significantly related to the presence of hepatosplenic disease. Hepatomegaly and splenomegaly were significantly more frequent in the heavy infection group. Anaemia, eosinophilia, raised ESR and an increase in both serum alkaline phosphatase and serum globulins were significantly related to the intensity of infection. On the other hand, haematological and biochemical changes, as well as histopathological changes, were more marked and severe in patients with hepatosplenic disease. For comparison, the findings of 117 patients with S. haematobium infections and of 41 with dual S. mansoni/S. haematobium infections are included.

Evidence is presented that female Anopheles farauti Laveran released in an alien village dispersed more, in their first oviposition cycle after release, than females released in their village of capture. In a subsidiary experiment transporting the mosquitoes did not affect dispersal; wind speed or direction was not sufficient to account for the phenomenon. It is hypothesized that these permanent-pool breeding mosquitoes make appetitive long-range flights to oviposition sites. Mosquitoes blood-fed before midnight had a shorter oviposition cycle than those fed just before dawn. Nulliparous females, and those with well-defined ovariolar dilatations, predominated in the early evening whereas females that had oviposited recently were largely collected in the middle and later parts of the night.

A cross sectional study of schistosomiasis in migrant labourers in the Sudan Gezira is described. The people examined were of two ethnic groups: (i) those of local Arabic origin and (ii) those from Western Sudan, West Africa or west of longitude 27 °E. These two migrant groups were examined in one area treated with molluscicide and in another that was not. Almost all the schistosome infections were with Schistosoma mansoni , with a prevalence of 57% over-all and up to 89% in particular groups. The prevalence was lower in the treated than in the untreated area, and slightly lower in the Arab nomads than in the others, except that it was markedly lower in females from the West in the treated area. These results are consistent with the known water-contact habits of the two migrant groups. An association was observed between infection and liver and spleen enlargement, but not between infection and other symptoms. The potential importance of migrants in transmitting the infection is discussed.

Niclosamide was used to interrupt transmission of Schistosoma haematobium by Bulinus senegalensis in seasonal rainwater pools for a period of three years. Snail populations were progressively reduced to approximately 1% of the numbers in untreated pools. There was little or no evidence of acquisition of new infection by children in the area during the period of intervention. The intensity of infection in a cohort of children initially under 10 years old followed for three years fell by more than 50%, while there was a ten-fold increase in a similar group in a nearby untreated area. The mean annual cost 1982 of control per head of the population protected was £0·50 (US$0·89).

After an interval of four years the same observers re-examined six rain-forest and six savanna villages, using the same standardized techniques. The results of these surveys have previously been reported by area, i.e. rain-forest and savanna. The present paper analyses the incidence of ocular changes by village. In the rain-forest the concentrations of microfilariae in the skin were similar in the six villages and there was, in general, little difference in the incidence and/or deterioration of ocular lesions between these villages. In the savanna the corresponding quantities were much higher in the three more heavily infected villages compared with the three less heavily infected ones. The implications of these findings for the control of blindness due to onchocerciasis in the savanna are discussed.

The results of an onchocerciasis survey of total populations aged 5 years and over in 22 village groups in Cameroon rain-forest and savanna are reported. Using standardized techniques the same observers examined skin and eye lesions in 2,678 persons infected with O. volvulus , and compared them with lesions in 1,156 persons in whom the parasite was not detected.