Onchocerciasis in southwestern Sudan: parasitological and clinical characteristics.

Parasitological and clinical observations were made on residents of Pongo Nuer, a village in the province of Bahr El Ghazal, southwestern Sudan. Of 202 skin biopsies, 189 (94%) were positive for microfilariae of Onchocerca volvulus. Nodules were most common around the pelvic girdle and rare on the limbs or head. Microfilarial intensities, ranging up to 1,094 mf/mg of skin, were highest at the iliac crest and shoulder; they increased rapidly in childhood but then appeared to reach a plateau maintained through adult life. Nodule presence and number, especially at multiple sites, was significantly related to skin microfilarial intensity. Dermal manifestations of O. volvulus infection were widespread and severe, ranging from acute maculopapular eruptions to chronic, diffuse, and degenerative changes, even in young adults. However, high skin microfilarial intensities were found in asymptomatic individuals; conversely, lowest intensities were in those with severest maculopapular lesions, suggesting that host response was a major determinant of disease outcome. Microfilariae were detected in the cornea or anterior chamber of the eyes of one third of those examined in all age groups, but lesions of the posterior segment, including optic neuritis, chorioretinitis, and pigmentary abnormalities, were considered responsible for visual deficits in the population sample. Some pathologic changes in the anterior segment attributable to microfilariae were more common in the young than in adults but there was no preponderance of sclerosing keratitis in adults, contrary to expectations in hyperexposed individuals in a Sudan savannah zone. The best correlate of the presence of microfilariae in the eye was the intensity of infection in shoulder skin snips. Little value could be derived from data on outer canthus samples, either in terms of severity of ocular infection or disease. Microfilaremia was common (76%) but in only one case was attributed to O. volvulus; the remainder were due to Mansonella perstans.

Onchocerca volvulus: enzyme polymorphism in relation to the differentiation of forest and savannah strains of this parasite.

Isozyme analysis was carried out on Onchocerca volvulus worms collected from Liberia, Ivory Coast, Burkina Faso and Sudan to see whether this technique could detect differences between forest and savannah populations of this parasite. A total of 243 forest and 189 savannah individual female worms were electrophoresed and stained for seven enzymes. Four showed some polymorphism, LDH, MDH, PGM and MPI and the other three, GAPDH, PEP and GPI were invariant. Statistical analysis of the results showed that the relative proportions of genotypes from within the different countries conformed to Hardy-Weinberg expectations. Pairwise comparisons of allele frequencies between countries showed that populations from Liberia and Ivory Coast had a very similar composition; there was some divergence between all the other pairs of populations and the genetic distance was calculated to summarize the degree of divergence. The number of loci examined was small and the genetic distances were within the range expected for separate geographical populations of the same species. The usefulness of this technique in worm identification is discussed.

Enzyme polymorphism in Trichinella.

The isoenzyme profiles of five isolates of the supposed 'species' of Trichinella, T. nativa, T. spiralis and T. nelsoni were compared. Four enzymes (AK, PGM, MPI and GPI) gave good resolution and clearly differentiated T. Spiralis from the other two species. T. nativa and T. nelsoni had similar isoenzyme patterns; the two separate isolates of T. nativa and T. spiralis used gave similar results, thus indicating the validity and the reproducibility of the technique. The value of enzyme electrophoresis for specific and subspecific classification of Trichinella is discussed and compared with the more traditional methods of taxonomy which have failed to resolve the controversy surrounding speciation.

Differentiation of species and life cycle stages of Brugia spp. by isoenzyme analysis.

The isoenzyme patterns of glucose phosphate isomerase and phosphoglucomutase of 3 species of Brugia, B. pahangi, subperiodic B. malayi, and B. patei, and 3 life cycle stages, adult, third-stage larva, and microfilaria were compared using the technique of isoelectricfocusing on polyacrylamide gels. The results demonstrated that the adults of all 3 species could be identified from one another and that differences existed between the sexes of any one species. Hybridization between B. pahangi and B. patei could be detected in the progeny of the cross. Both the third-stage larvae and microfilariae of B. malayi and B. pahangi were differentiated and the epidemiological significance and the application of these findings to arthropod-borne filarial infections were discussed.

Macaca fascicularis, a nonpermissive host for the human filarial parasite Loa loa.

The ability of the filarial nematode Loa loa to infect 2 species of primates was studied. The primate species selected were closely related to species known to be susceptible. A mandrill (Mandrillus sphinx) and 6 cynomolgus monkeys (Macaca fascularis) were infected by subcutaneous injection of third-stage larvae of human L. loa from Gabon. The mandrill developed microfilaremia with an estimated prepatent period of 147 days, but microfilariae were not detected in any of the cynomolgus monkeys. Thus, mandrills appear permissive to human L. loa, whereas cynomolgus monkeys are not. Serum antibody responses were examined on western blots of adult L. loa antigens. Preinfection sera from all animals gave no reactions, but, after infection, sera from cynomolgus monkeys reacted more intensely and with more antigens than mandrill sera. Antibodies were still detectable in cynomolgus monkeys 15 mo postinfection. These reactions were compared with those found using human infection sera. Reactions with the cynomolgus monkey sera resembled those found with resistant endemic and amicrofilaremic human sera.

The identification of some Onchocerca spp of cattle by isoenzyme analysis.

The isoenzyme patterns of LDH, MDH, PEP, PGM, MPI, GPI and GAPDH were compared for 3 species of cattle parasites Onchocerca gutturosa, O. gibsoni and O. lienalis from England, Australia and Mexico. LDH and GAPDH had identical patterns in each species but the other enzymes clearly distinguished between the species. PGM was the same in O. lienalis and O. gibsoni, but separated them from O. gutturosa. MPI and GPI had similar isoenzymes in O. gutturosa and O. gibsoni, but distinguished them from O. lienalis. Different isoenzyme patterns for all 3 species were obtained with MDH and PEP. The potential use of these techniques towards a better understanding of the epidemiology of human onchocerciasis is discussed.

Demonstration of antibodies to phosphoglucomutase of parasitic origin in Brugia pahangi-infected cats.

Antibodies inhibitory to the activity of the enzyme phosphoglucomutase (PGM) EC 2.7.5.1. of Brugia pahangi adult worm were demonstrated in sera from five rabbits immunized against this filarioid and from 5 of 27 cats infected with B. pahangi, by isoelectricfocusing and spectrophotometric techniques. This anti-PGM activity was species- and stage-specific. This raises the possibility of using species-specific isoenzymes of parasitic origin as antigens in serological tests.

Morphological characteristics and isoenzyme patterns of an Onchocerca sp. found in cattle in Southern Mexico.

An Onchocerca sp. was isolated from the nuchal ligaments of 78 out of 79 naturally infected cattle in Southern Mexico. Infections were moderate to heavy, averaging 20-30 parasites per nuchal ligament. Microfilariae were concentrated in the skin of the head and neck, although small numbers were found in the skin of the withers, brisket and medial abdomen. High numbers of microfilariae were found in the skin around the eye, but not in the ocular tissues themselves a situation dissimilar to that found in human onchocerciasis. Morphologically, adult females, males and microfilariae were identified as being O. gutturosa. Analysis of the isoenzyme patterns of LDH, MDH, PGM, GPI, PGD and ES of adult female worms, showed the Mexican parasite to be the same as O. gutturosa from England and Australia.