Observations on cattle schistosomiasis in the Sudan, a study in comparative medicine. II. Experimental demonstration of naturally acquired resistance to Schistosoma bovis.

Epizootiological observations on Schistosoma bovis in cattle at Kosti, Sudan, showed a significant fall in age-specific prevalence and intensity with age, based on fecal egg count. To test the possibility that this is due to acquired resistance, Kosti cattle and a control group of cattle of similiar breed and age from a nonenzootic area were experimentally challenged with 70,000 S. bovis cercariae. Clinical observations showed very clearly that the Kosti cattle were able to withstand almost completely the effects of the challenge, whereas the controls developed lethal infections. Resistance was further demonstrated by clear differences between the two groups in terms of their body weights, hematological measurements, histopathological and pathophysiological responses, and worm and egg counts. The data suggested that the main basis of the resistance was a suppression of egg production by the worms from the challenge, rather than absolute prevention of their maturation. There was also evidence of a suppression of the fecundity of worms in the naturally infected Kosti cattle.

Observations on cattle schistosomiasis in the Sudan, a study in comparative medicine. III. Field testing of an irradiated Schistosoma bovis vaccine.

Previous work has shown that cattle can acquire a strong resistance to Schistosoma bovis infection following repeated natural exposure. Partial resistance to a laboratory challenge with S. bovis has also been demonstrated in calves after immunization with an irradiated schistosomular or cercarial vaccine. The aim of the present study was to see whether this type of vaccine could protect calves under the very different conditions of natural exposure to S. bovis in the field. Thirty 6- to 9-month-old calves were each immunized with 10,000 irradiated S. bovis schistosomula by intramuscular injection and 8 weeks later were released into an enzootic area along with 30 unvaccinated animals. The calves were followed up for 10 months, during which period protection was evidenced by a lower mortality rate, a slower rate of acquisition of infection, and lower fecal egg counts in the vaccinated calves. Necropsy of the survivors showed 60--70% reductions in worm and tissue egg counts of the vaccinated calves as compared to those not vaccinated.

Observations on cattle schistosomiasis in the Sudan, a study in comparative medicine. I. Epizootiological observations on Schistosoma bovis in the White Nile Province.

A 2-year epizootiological study was carried out on Schistosoma bovis in cattle in an enzootic area of the Sudan. The prevalence of infection, as judged by the Pitchford fecal egg counting technique, was very high, approaching 90% in 1.5-year-old animals. There was, however, a lower prevalence in older cattle, and this trend was also seen with the fecal egg counts. This suggests that the cattle gradually acquire resistance to reinfection, particularly since there seems to be little age-related variation in the amount of water contact. Monthly incidence rates, estimated from fecal examinations of initially uninfected "tracer" calves showed a marked seasonal pattern, being much higher in the hot summer months, and snail infection rates showed a similar seasonal pattern. In addition, both the monthly incidence measurements and the snail infection rates showed that transmission was much heavier in 1976 than in 1977. Epizootics such as those recorded previously in this area presumably arise from exceptionally intense transmission years.

The incidence of eye lesions and visual impairment in onchocerciasis in relationship to the intensity of infection.

Data from follow-up surveys of onchocerciasis, conducted in the rain-forest and savanna areas of the United Cameroon Republic, are used to fit equations relating the incidence of eye lesions and visual impairment to microfilaria concentration in skin-snips. The incidence of lesions in those aged under 45 appears to be directly proportional to concentration, though the association is less clear in females over 25 in the savanna. The incidence of visual impairment appears also to be directly proportional to concentration among those under 45, but only in the savanna. Predictions of changes in incidence rates under transmission control are made, using hypothetical values for the rate of decline of infection. They are compared with reported incidence of lesions from the Onchocerciasis Control Programme: they are in good agreement for those aged under 30 years, but they understate the observed decline in older subjects.

Studies on onchocerciasis in the United Cameroon Republic. III. A four year follow-up of 6 rain-forest and 6 Sudan-savanna villages.

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 rainforest 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.

Dynamics of schistosoma haematobium infection in a Gambian community. II. The effect on transmission of the control of Bulinus senegalensis by the use of niclosamide.

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 pound 0.50 (US $0.89).

The significance of proteinuria and haematuria in Schistosoma haematobium infection.

The intensity and prevalence of proteinuria and haematuria were studied with urinanalysis reagent strips in a Gambian community in which the intensity of infection with Schistosoma haematobium was high. The level of proteinuria present was shown to be related to the intensity of infection. Follow-up for 12 months showed that infected subjects with heavy proteinuria had a good prognosis. These findings suggest that the urinary protein in such subjects is likely to originate from lesions in the bladder and ureters and that advanced glomerular pathology is probably rare. The relationship of the levels of proteinuria and haematuria to the egg count suggests they may be parameters which could have value as indications for chemotherapy. Detailed study showed that the effect of treating all the subjects who had both 30 mg/100 ml or more of protein and at least a trace of haematuria would have been very similar to treating all those with an egg count of 200 ova/10 ml or more. Since urinalysis with reagent strips is very simple and rapid it could have a role in mass chemotherapy campaigns, particularly those aimed at the identification and treatment of heavily infected subjects.

Comparative xenodiagnosis with three triatomine species of different hosts with natural and experimental chronic infections with Trypanosoma (Schizotrypanum) cruzi.

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 with 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.

The use of infectivity titrations for measurement of the viability of Entamoeba histolytica after cryopreservation.

An infectivity titration technique is described for the measurement of the viability of Entamoeba histolytica. Using this method an optimal cryopreservation technique has been developed. When amoebae from young cultures were equilibrated with 7.5% dimethylsulphoxide for 15 minutes at 37 degrees C, cooled to -100 degrees C at 1 degree C per minute, and stored in liquid nitrogen, 1 to 2% regularly survived after thawing rapidly at 37 degrees C and, on occasions, 10 to 12% survived.

Dynamics of Schistosoma haematobium infection in a Gambian community. I. The pattern of human infection in the study area.

The roles of some of the factors thought to be responsible for the characteristic relationship between age and the intensity and prevalence of Schistosoma haematobium infection have been investigated. In this initial report a study population in an area of intense infection is described, as are the methods used. Subsequent papers report the effect of interrupting transmission with molluscicide in part of the area and compare changes in egg count in this treated area with changes in an area where no intervention took place. These allow a consideration of age-specific rates of loss and acquisition of infection to be made. The intensity and prevalence of infection varied between villages both in the treated and untreated areas, but the relation of age to the pattern of infection was regardless of the level of infection in the villages. Over-all, the number of subjects and their pattern of infection was similar in both areas. The prevalence of infection tended to be higher in adult males than females but preliminary water contact observations suggest males are less exposed to infection. Observations over the three-year study period emphasize the extent of population movement in the study area and point to its importance in the planning of control measures.

Dynamics of Schistosoma haematobium infection in a Gambian community. III. Acquisition and loss of infection.

During a three-year period of effective control of Schistosoma haematobium transmission by molluscicide application the mean number of S. haematobium ova passed by subjects in the treated area fell in an exponential manner which suggested that the mean life span of the worm was 3.4 years. Parallel observations were made in a similar but untreated area. A comparison of the observations in these two areas suggested that in the untreated area subjects of all ages acquired infection during the course of the study. At the end of the study over 50% of the egg output in most age groups in the untreated area appeared to come from worms acquired during the preceding three years. There were substantial differences between age groups in the amount of infection acquired. Children, aged between eight and ten years at the end of the study, appeared to be passing perhaps a thousand times more ova from worms acquired during the preceding three years than were middle-aged subjects. Preliminary observations suggest that age- and sex-related differences in the pattern of water contact may not fully account for age- and sex-related differences in the rate of acquisition of infection and its prevalence. The probable significance of protective immunity in the epidemiology of schistosome infections is discussed.

Migrant workers and schistosomiasis in the Gezira, Sudan.

A cross sectional study of schistosomiasis in migrant laboureres 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 degrees 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.

Studies on onchocerciasis in the United Cameroon Republic. IV. A four-year follow-up of six rain-forest and six savanna villages. The incidence of ocular lesions.

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 immune response to a meningococcal polysaccharide vaccine in an African village.

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.

Arbovirus infections in Sarawak: the role of the domestic pig.

The possible role of pigs as arbovirus maintenance hosts and their importance as amplifier hosts was studied. Blood samples from 464 pigs of all ages collected in 1962 and 1964 were tested against 10 arboviruses. Antibodies to Japanese encephalitis and Getah viruses were particularly prevalent and their calculated monthly infection rates were 19-5% and 13-3% respectively. In 1969, 447 pigs were bled monthly throughout the year and the infection rates for Japanese encephalitis virus were calculated in pigs during the first year of life. Infection rates were not uniform throughout the year; the rate increases as the pig grew older and there was a marked seasonal increase in the infection rate in the period from November to January. This coincided with the seasonal major population peak of Culex tritaeniorhynchus following intense breeding of this mosquito prior to rice planting. It is suggested that, in Sarawak, the pig acts as a maintenance host of Japanese encephalitis in a cycle involving C. gelidus mosquitoes and also acts as an important amplifier host towards the end of the year in a cycle involving C. tritaeniorhynchus. It is further suggested that Getah virus is maintained in a similar cycle between C. tritaeniorhynchus and pigs.

Tanzania filariasis project. Survey methodology and clinical manifestations of bancroftian filariasis.

In a Bancroftian filariasis survey on the coast of Tanzania microfilaria rates rose with age reaching 53% in the 60-69 year group followed by a slight fall above this age. The most important clinical manifestations were hydrocoele, funiculitis and elephantiasis, with hydrocoele presenting the most serious public health problem. Hydrocoele rates increased with age reaching 90% above the age of 70. The highest proportion of large hydrocoeles were also in the older age groups. A satisfactory methodology was established for the planning of future surveys leading to control.

Tanzania filariasis project: studies on microfilaraemia and selected clinical manifestations of Bancroftian filariasis.

In a total of 1977 males aged 5 years and over examined in 21 cluster samples on the coast of Tanzania, the overall rate for microfilariae of Wuchereria bancrofti was 32%. Hydrocoele and elephantiasis rates were 39% and 3%, respectively. The rates and severity of these 2 clinical manifestations increased in the older age groups. Both the microfilarial density and prevalence increased rapidly in the early age groups, followed by a levelling off and then a slight fall in old age. There was no association between microfilarial densities or rates and the overall prevalence of hydrocoele, but a negative association was demonstrated between microfilaraemia and hydrocoeles and elephantiasis. A comparison between the length of residence in an endemic area and the microfilarial and clinical sign rates showed evidence for the long incubation period for W. bancrofti and for the slow development of hydrocoeles and elephantiasis.

Diarrhoea and growth faltering in rural Zimbabwe.

OBJECTIVE: To assess the evidence that diarrhoea is an important cause of growth faltering in young children in developing countries. DESIGN: Prospective, longitudinal cohort study. SETTING: Worker's compounds on commercial farms in Shamva, rural Zimbabwe. SUBJECTS: 204 children < 12 months old were enrolled, 73 from birth. The median age at enrolment was 4 months. Eleven children died and 39 were lost to follow-up. INTERVENTIONS: Prospective weekly diarrhoea surveillance by farm health workers and monthly anthropometry. RESULTS: Growth faltering was severe, but there was little difference in average rates of growth between children with frequent diarrhoea and infrequent diarrhoea. The results of an interval-based data analysis were consistent with there being only a transient effect of diarrhoea on weight gain. Estimation of weight faltering following episodes of diarrhoea and the rate of return to the trend in the 9-14 month age range, indicated that weight loss associated with each episode was small (approximately 2%) and return to the child's trend was 90% complete within a month. At older ages than this, weight loss appeared to be less, and estimates were not statistically significant. CONCLUSIONS: These observations lend weight to the hypothesis that recurrent episodes of diarrhoea are not a potent cause of growth faltering in early childhood except in a small minority of largely catastrophic cases. Inadequate food intake is a more plausible explanation.

PIP: In Zimbabwe, health workers collected data on diarrhea incidence every week and anthropometric data once a month from 204 children aged less than 12 months to examine the association between diarrhea and growth faltering. 73 children were enrolled at birth. 148 children were followed throughout the entire study. 11 children died (8 because of diarrhea or protein-energy malnutrition). 39 children were lost to follow-up. The children's parents were farm laborers who lived on large-scale commercial farms in Shamva district. Diarrhea incidence peaked between 13 and 18 months. In 91% of attacks, the diarrhea was watery rather than bloody. 31 children had more than 9 diarrhea episodes (high diarrhea frequency). 25 had no more than 4 diarrhea episodes (low diarrhea frequency). There was little difference in the children's mean weight and mean length from 1 to 30 months of age between high and low diarrhea frequency subjects. The average loss of overall growth per diarrhea episode in the age range 9-23 months was 51 g and 0.18 cm. In the age range of 9-14 months, weight loss after the diarrhea episode was 2.3% of body weight, and 90% of the sudden weight decline below the child's trend was recovered in 30 days. Weight loss was less than 2.3% among older children. A 2.3% weight loss in an 8 kg child is 180 g. Assuming that diarrhea is responsible for the entire weight loss (about 66 g/episode), the reduction in overall growth is about 120 g (1.5%). The total energy needed to accumulate 120 g is 480 kcal; thus, a child would require an additional 2-3 kcal/kg/day (a small amount) to gain 120 g. These findings support the hypothesis that recurrent diarrhea episodes do not induce growth faltering except in a few cases. Inadequate food intake is a more plausible explanation.