T.F. de C. Marshall

Numerical analysis of enzyme polymorphism: a new approach to the epidemiology and taxonomy of trypanosomes of the subgenus Trypanozoon.

Publisher Summary The subgenus Trypanozoon contains several kinds of trypanosome, which are morphologically indistinguishable but differ in their behavior. At various times specific or subspecific status has been accorded to each kind, but, in recent years, those cyclically transmitted by tsetse in Africa have been separated into subspecies of Trypanosoma brucei , while the others, transmitted non-cyclically outside the African tsetse belts, have retained separate species status. However, although such new terminology may be more correct taxonomically, the practical problems of distinguishing the trypanosomes remain. Enzyme electrophoresis is being used on an increasingly wide scale for the intrinsic characterization. However, as the number of enzyme systems being used for identification grows, comparison of stocks becomes increasingly difficult and intricate, particularly when an enzyme occurs in a multibanded form after electrophoresis. After using 12 enzyme systems to characterize 160 Trypanozoon stocks, the results have been analyzed to establish the degree of relatedness of each of the 59 zymodemest encountered. The detailed analysis is presented in this chapter.

PNEUMOCOCCAL VACCINE PREVENTS DEATH FROM ACUTE LOWER-RESPIRATORY-TRACT INFECTIONS IN PAPUA NEW GUINEAN CHILDREN

In three double-blind placebo-controlled trials of pneumococcal capsular polysaccharide vaccines against death from acute lower-respiratory-tract infections (ALRI), children were vaccinated at 6 months to 5 years of age. The efficacy of the vaccines against ALRI as the sole cause of death was estimated at 59% in children vaccinated when younger than 5 years (p = 0.008) and 50% in children vaccinated when younger than 2 years (p = 0.043). Mortality from all causes was 19% less in the vaccinated group.

Studies on onchocerciasis in the United Cameroon Republic. II. Comparison of onchocerciasis in rain-forest and Sudan-Savanna

Abstract 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.

Bancroftian filariasis: a comparison of microfilariae counting techniques using counting chamber, standard slide and membrane (nuclepore) filtration.

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.

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.

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.

Immunization of calves against Schistosoma bovis using irradiated cercariae or schistosomula of S. bovis

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.

Studies on onchocerciasis in the United Cameroon Republic. I. Comparison of populations with and without Onchocerca volvulus

Abstract 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.

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.

Evidence for a ‘memorized’ home range in Anopheles farauti females from Papua New Guinea

Abstract. 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.