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.

Studies in the White Nile area of the Sudan have shown that Zebu cattle acquire a high degree of resistance to Schistosoma bovis as a result of repeated natural exposures without, however, being able to eliminate their populations of adult schistosomes, although these do show greatly suppressed fecundity. To test whether these adult worms are necessary for the maintenance of resistance we cured six "naturally resistant" cattle (TC group) with a double treatment of 25 mg/kg praziquantel and compared their response to a 70,000 cercariae challenge with groups of "naturally resistant" but untreated cattle (UC group) and with previously unexposed, challenged cattle (CC group). Challenge was carried out 7 weeks after the second dose of praziquantel. The results confirmed that untreated cattle are "naturally resistant" and also showed that resistance was not abrogated by cure of the naturally-acquired infections. Thus, fecal egg counts after challenge reached mean maxima of 2,432 eggs per gram (epg) in the CC, but only 5 epg and 28 epg in the TC and UC groups, respectively. Similarly, mean worm counts were 85% and 69% lower in the TC and UC groups, respectively, and mean tissue egg densities were reduced by 72-99%, and 56-80%. Histopathologically, the TC and UC groups were also far less affected than the CC. Effective praziquantel treatment does therefore not destroy naturally acquired resistance to S. bovis, and may benefit infected livestock even in the absence of transmission control. The situation in human schistosomiasis is less clear, but there are several epidemiological and experimental indications of a similar conclusion for S. mansoni.

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.

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.

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.

This paper describes further characteristics of the immunization of sheep against schistosomes using live, irradiation 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.

Three techniques were compared for counting microfilariae of Wuchereria bancrofti in blood specimens--a standard slide method, the counting chamber technique (CCT) and a membrane filtration technique (MFCT). The CCT was much more sensitive than the slide method, the difference in sensitivity between these two methods probably being due mainly to the loss of microfilariae during the dehaemoglobinizing process prior to staining in the standard slide method. There was good correlation between the techniques when 0.1 ml of finger-prick blood was examined by the CCT and 1 ml of venous blood by the MFCT. The number of additional positives revealed by the MFCT was ten of 275 (3.6%) subjects examined. The use of venepuncture for MFCT is impractical for field surveys in East Africa whereas a microfilarial count on 0.1 ml of finger-prick blood meets most of the criteria required of a field technique. The method is simple, quantitative and acceptable to the population. The results are reproducible, can be readily checked, the technique provides a useful and practical method for obtaining prevalence information following control schemes. The finding of a relatively low prevalence of microfilariae seen by both MFCT and CCT in children aged five to nine years from a highly endemic filariasis area agrees with the results of previous East African surveys carried out by blood smear and CCT.

A single 10-14 day course of diethylcarbamazine (DEC) was given under betamethazone cover to 18 patients (Group A) with ocular onchocerciasis, and the effects were studied in detail over 1-2 years. A comparison was made with the findings in 21 patients (Group B) who received a similar course to be followed by a weekly suppressive 100-200 mg dose of DEC. A further 18 patients (Group C) served as controls. The initial DEC course provoked severe general reactions, but ocular complications could be controlled by betamethazone. The weekly suppressive dose was not acceptable to the majority of patients, and only one young patient with severe iritis who improved during the initial course took the weekly tablet voluntarily over 2 years. The initial DEC course reduced the numbers of microfilariae in the eye and was of temporary benefit to lesions of the anterior segment, but it did not affect lesions of the posterior segment. A possible adverse effect on the optic disc is discussed. Any beneficial long term effect was almost confined to Group B, and to lesions of the anterior segment. The best to hope for in lesions of the posterior segment was arrest of further development. The findings at the end of the trial were as follows: No. of lesions (see article).

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.

Results of xenodiagnosis and haemoculture of 44 different animal and human subjects were compared quantitatively by linear logistic analysis.

Summary Fourteen 9-month-old zebu calves were immunized with 10000 irradiated Schistosoma bovis schistosomula given in 1–3 intramuscular or subcutaneous doses, and 4 more calves were immunized with 10000 irradiated cercariae administered percutaneously in a single dose. Eight weeks after the beginning of the experiment these calves, together with four non-immunized controls were challenged percutaneously with 10000 normal S. bovis cercariae/calf. Comparative clinical, parasitological, pathological and pathophysiological observations subsequently revealed significant differences between the vaccinated and non-vaccinated calves. The vaccinated calves showed significantly higher growth rates, and a superior body composition as indicated by their lower total body water content. The beneficial effects of vaccination were also shown by significantly lower faecal egg outputs in the vaccinated calves and by their lower tissue egg and adult worm counts. The reduced tissue egg counts were also reflected in the milder histopathological changes seen in the vaccinated calves. The vaccinated calves had significantly higher packed cell and circulating red blood cell volumes than the challenged controls, longer red blood cell half lives, and somewhat lower blood volumes and rates of red blood cell synthesis. No untoward clinical effects that could be attributed to vaccination were recorded. These results indicate that zebu cattle can be effectively protected against S. bovis by vaccination with irradiated organisms. We are now evaluating this type of vaccine in a field trial in an enzootic area in the Sudan.

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 experiment described was conducted in water impounded by earth dams, for local water-supply, in Nyanza province, Kenya. Control of snails was attempted by introduction of the malacophagous fish Astatoreochromis alluaudi; other species were also introduced. The schedules of introduction of fish were varied between the reservoirs, and one was left as a control without any introduction of fish. The necessity for the establishment of a fish-rearing pond, prior to large-scale stocking, is emphasized.Assessment of snail control was made by scooping for snails, catches being expressed per man-hour. This was carried out both before and after introduction of fish, over a total period of 15 years. It is concluded that the data indicate that A. alluaudi did reduce the numbers of some species of snails—particularly Biomphalaria pfeifferi and, to a lesser extent and with less certainty, Bulinus spp.Two other introduced fish species, Tilapia zillii and T. leucosticta, did not appear to be associated with any fall in snail numbers.

Repeated multiple skin snips in 18 persons with onchocerciasis from the Sudan-savanna of West Africa suggested the possibility of a seasonal variation in microfilarial concentrations. This variation may be an evolutionary adaptation of the parasite to the climate conditions that affect the seasonal distribution of the vector, but a migration of the microfilariae in the skin layers caused by the Simulium bites cannot be excluded.

In a population survey in 1970/72 the prevalence of head nodules was found to be 1.7% in 1098 cases of onchocerciasis in the rain-forest and 0.6% in 1128 cases in the Sudan-savanna of Cameroon. In a follow-up survey in the same villages 3-4 years later more attention was given to the detection of head nocules, and the corresponding prevalences were 5.5 and 5.0%. In the follow-up survey a strong associated was demonstrated between the presence of head nodules and lesions of both the anterior and posterior segments of the eye. The relative risks of having eye lesions in patients with head nodules compared with those without were 2.9 and 7.5 in the rain-forest and savanna respectively. In a group of 483 clinic cases with ocular onchocerciasis from the savanna palpable head nodules were detected in 23.6%, and in a further 140 selected cases from the same area with posterior segment eye lesions, head nodules were detected in 31.4%. Confirmation of the onchocercal origin of the nodules was obtained in doubtful cases by biopsy. Many head nodules probably remain undetected in onchocerciasis surveys. They are often very small, flat, and hard, and tightly adherent to the under-lying periosteum, and the patient will often point out the presence of a nodule even when none has been detected after careful examination. The presence of a head nodule has long been one of the recognized "risk factors" associated with a high prevalence of blindness in Central America, but there have been no detailed studied in African onchocerciasis. A trial is in progress to assess the effect of nodulectomy on the development of ocular lesions.

39 patients (Group A) with ocular onchocerciasis in the Sudan-savanna of north Cameroon were given 4-6 g of suramin and followed in detail over 1-2 years. 39 other patients (Group B) received suramin followed 2 weeks later by a 6-7 day course of diethylcarbamazine (DEC). A further 18 patients (Group C) received placebo injections and were followed in the same way by the same observers. Suramin caused serious general reactions among the 100 patients who started the course - 1 case of stomatitis, 1 exfoliative dermatitis, and several cases of severe prostration, among which 2 ended fatally. These reactions underline the urgency for further studies on the toxicity of suramin, which is without doubt an efficient macro- and micro-filaricidal drug. Changes which occurred in the ocular lesions are described in detail. There was an initial aggravation of punctate and sclerosing keratitis, and sometimes a serious aggravation or development of anterior uveitis, corresponding to the peak microfilaricidal effect of the drug. The possibility of a simultaneous adverse effect on the optic disc is discussed. Despite these reactions, which might have been avoided by prior elimination of microfilariae by DEC, the eyes were in general quieter at 3 months and thereafter than before treatment. However, no posterior segment lesion improved after suramin, and the majority remained unchanged. The findings at the end of the trial were as follows: No. of lesions (see article).

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 increased 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.

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.