The distribution of microfilariae in the skin of Guatemalan onchocerciasis patients: an evaluation of diagnostic potentials

Onchocerca-Simulium interactions and the population and evolutionary biology of Onchocerca volvulus

Parasite-vector interactions shape the population dynamics of vector-borne infections and contribute to observed epidemiological patterns. Also, parasites and their vectors may co-evolve, giving rise to locally adapted combinations or complexes with the potential to stabilise the infection. Here, we focus on Onchocerca-Simulium interactions with particular reference to the transmission dynamics of human onchocerciasis. A wide range of simuliid species may act as vectors of Onchocerca volvulus, each exerting their own influence over the local epidemiology and the feasibility of controlling/eliminating the infection. Firstly, current understanding of the processes involved in parasite acquisition by, and development within, different Simulium species in West Africa and Latin America will be reviewed. A description of how Onchocerca and Simulium exert reciprocal effects on each other's survival at various stages of the parasite's life cycle within the blackfly, and may have adapted to minimise deleterious effects on fitness and maximise transmission will be given. Second, we describe the interactions in terms of resultant (positive and negative) density-dependent processes that regulate parasite abundance, and discuss their incorporation into mathematical models that provide useful qualitative insight regarding transmission breakpoints. Finally, we examine the interactions' influence upon the evolution of anthelmintic resistance, and conclude that local adaptation of Onchocerca-Simulium complexes will influence the feasibility of eliminating the parasite reservoir in different foci.

Onchocerciasis in the Blue Nile Valley of western Ethiopia

In a survey among 477 inhabitants of the Blue Nile Valley of western Ethiopia 182 (38%) were positive by skin snip investigation for microfilariae of Onchocerca volvulus. Of these only 23% had typical clinical signs and symptoms of onchocerciasis. The highest prevalence rate of microfilariae (84%) was found among Nilotics in the lowlands, where 50% of the children above 10 years, and 90% of adults above 30 years of age, were infected. The mean microfilarial density per skin snip was significantly higher in the high prevalence areas (14) than in the low prevalence areas (3). Positive skin snips from both hip and shoulder were found in 24% of the population, whereas 3% had microfilariae only in the shoulder and 11% only in the hip region. The mean microfilarial density in the hips (16) was double that in the shoulders (8). Ophthalmological evaluation, including slit lamp examination, was possible in 77 of the 182 cases with positive skin snips. Severe eye damage due to onchocerciasis was not observed. However, one 35 year old female had live microfilariae in the anterior chambers of both eyes.

The status of human filariasis in relation to clinical signs in endemic areas of the Niger Delta

A study was carried out in selected parts of the Niger Delta Basin on human filariasis and its relationship to clinical signs. One hundred and seventy-six (13.0%) of 1351 individuals examined were infected with microfilaria. Forty-six percent of microfilaria positive cases had M. perstans; 25.6% had W. bancrofti, 19.3% had L. loa, and 9.0% had O. volvulus. The prevalence of filariasis increased with age. Microfilarial density was generally low, 28.4% of infected individuals had counts of 50-100 microfilaria per 20 mm3 blood, 12.5% had counts less than five microfilaria per 20 mm3 blood. Onchocerca microfilariae did not exceed five microfilaria per snip. Microfilarial density was high among individuals aged between 20 and 49 years, but declined with increasing age above 50 years. Acute clinical signs of febrile attack, sink eruptions, and chronic clinical signs of chyluria, hydrocoele, elephantiasis and ocular lesions were observed in 61.9% of infected individuals, 73.4% of clinical cases were febrile attack and skin eruptions, 5.5% were chyluria, 12.8% were elephantiasis of the leg and scrotum, 7.3% were hydrocoele and 0.9% were ocular lesions. Chronic clinical signs were more prevalent in individuals over 40 years of age.

IgM rheumatoid factors in Guatemalan onchocerciasis

The possible presence of IgM Rheumatoid factors (RF) and anti-DNA antibodies was investigated in sera of patients with Guatemalan onchocerciasis. The mean value of IgM RF in the patients was found to be significantly higher than that in controls and 10 out of 57 patients had increased levels of IgM RF. In addition, serum IgM levels in those 10 patients with increased levels of IgM RF were significantly elevated. In contrast, no significant increase of serum anti-single-stranded (ssDNA) and double-stranded DNA (dsDNA) antibodies were found in the patients.

The distribution of the microfilariae of Onchocerca volvulus in the different body regions in relation to the attacking behaviour of Simulium damnosum s.l. in the Sudan savanna of northern Cameroon

Densities of Onchocerca volvulus microfilariae in four volunteers with low to moderate infections were estimated at five body sites by paired skin snips. The landing of Simulium damnosum s.1. females on the body of these volunteers was recorded during 12 hours for six days. Most flies fed at the ankles (53% and 51%) and calves (28% and 27% respectively) in both the standing and sitting positions. The density of microfilariae in the skin was highest in the pelvic region (24.1 mf/mg) and relatively low in the calf (14.8 mf/mg) and ankle (1.0 mf/mg) regions. From the biting rate (females/body part) and the microfilarial density (mf/mg) a transmission index was calculated for the different body regions. This was highest for the calves showing that this part of the leg, if unclothed, accounts for the highest rate of contact (50 to 60% of total) between vector and parasite.