The onchocerciasis focus at Kinsuka/Kinshasa (Republic of Zaire) in 1985. II. Parasitological and clinical aspects

Onchocerciasis transmission status in some endemic communities of Cross River State, Nigeria after two decades of mass drug administration with ivermectin

Onchocerciasis is a parasitic disease transmitted by black flies. Human onchocerciasis is a public health and socioeconomic problem in Nigeria. Its prevalence and morbidity have reduced over the years because of control efforts especially, Mass Drug Administration with ivermectin. The current goal is to eliminate the disease transmission by 2030. Understanding the changes in transmission patterns in Cross River State is critical to elimination of onchocerciasis in Nigeria. This study was designed to determine the transmission dynamics of onchocerciasis in Cross River State after over two decades of mass ivermectin distribution in endemic communities. Agbokim, Aningeje, Ekong Anaku and Orimekpang are four endemic communities from three Local Government Areas of the State selected for this study. Transmission indices such as infectivity rates, biting rates and transmission potentials, parity rates and diurnal biting activities were determined. A total of 15,520 adult female flies were caught on human baits, Agbokim (2831), Aningeje (6209), Ekong Anaku (4364) and Orimekpang (2116). A total of 9488 and 5695 flies were collected during the rainy and dry seasons respectively in the four communities studied. The differences in relative abundance among the communities were statistically significant (P < 0.001). Monthly and seasonal fly numbers varied significantly (P < 0.008). There were differences in diurnal biting activities of flies in this study at different hours of the day and different months. The peak monthly biting rates were 5993 (Agbokim, October), 13,134 (Aningeje, October), 8680 (Ekong Anaku, October) and 6120 (Orimekpang, September) bites/person/month while the lowest monthly biting rates were 400 (Agbokim, November), 2862 (Aningeje, August), 1405 (Ekong Anaku, January) and 0.0 (Orimekpang, November and December) bites/person/month. Differences in biting rates among the study communities were significant (P < 0.001). The peak monthly transmission potential in Aningeje was 160 infective bites/person/month in the month of February while the lowest (except for months with no transmission) was 42 infective bites/person/month in the month of April. All other study sites had no ongoing transmission in this study. Transmission studies showed that there is progress toward transmission interruption especially in 3 out of the four studied areas. Molecular O-150 poolscreen studies is required to confirm the true transmission situation in the areas.

How does onchocerciasis-related skin and eye disease in Africa depend on cumulative exposure to infection and mass treatment?

BACKGROUND

Onchocerciasis (river-blindness) in Africa is targeted for elimination through mass drug administration (MDA) with ivermectin. Onchocerciasis may cause various types of skin and eye disease. Predicting the impact of MDA on onchocercal morbidity is useful for future policy development. Here, we introduce a new disease module within the established ONCHOSIM model to predict trends over time in prevalence of onchocercal morbidity.

METHODS

We developed novel generic model concepts for development of symptoms due to cumulative exposure to dead microfilariae, accommodating both reversible (acute) and irreversible (chronic) symptoms. The model was calibrated to reproduce pre-control age patterns and associations between prevalences of infection, eye disease, and various types of skin disease as observed in a large set of population-based studies. We then used the new disease module to predict the impact of MDA on morbidity prevalence over a 30-year time frame for various scenarios.

RESULTS

ONCHOSIM reproduced observed age-patterns in disease and community-level associations between infection and disease reasonably well. For highly endemic settings with 30 years of annual MDA at 60% coverage, the model predicted a 70% to 89% reduction in prevalence of chronic morbidity. This relative decline was similar with higher MDA coverage and only somewhat higher for settings with lower pre-control endemicity. The decline in prevalence was lowest for mild depigmentation and visual impairment. The prevalence of acute clinical manifestations (severe itch, reactive skin disease) declined by 95% to 100% after 30 years of annual MDA, regardless of pre-control endemicity.

CONCLUSION

We present generic model concepts for predicting trends in acute and chronic symptoms due to history of exposure to parasitic worm infections, and apply this to onchocerciasis. Our predictions suggest that onchocercal morbidity, in particular chronic manifestations, will remain a public health concern in many epidemiological settings in Africa, even after 30 years of MDA.

[A text-book case of tropical facial elephantiasis]

INTRODUCTION

Tropical facial elephantiasis is a nosological entity which can arise from various underlying causes: von Recklinghausen neurofibromatosis, lymphatic and cutaneodermal filarioses, deep mycosis.

CASE REPORT

We report an exceptional case of tropical facial elephantiasis caused by onchocercosis and entomophtoromycosis (rhinophycomycosis). The patient's facial morphology was noted "hippopotamus-face" or "dog-face".

DISCUSSION

Onchocercosis and entomophtoromycosis are two diseases known to cause facial elephantiasis. We have not however been able to find any case report in the literature of co-morbidity nor any information on factors predictive of concomitant occurrence.

Chemotherapy of filariases

The filarial parasites that affect humans most seriously include Onchocerca volvulus, Wuchereria bancrofti, Brugia malayi and Loa loa. In general, these species cause disease that is debilitating long before it is fatal, producing clinical manifestations such as general malaise, pruritus and lichenification of the skin, lymphangitis, elephantiasis and blindness(1). As a result, infection with any one of these organisms is physically, as well as economically, devastating. Currently, the pharmacological armamentarium with which to treat filarial infections is very limited and many of the drugs that are known to be efficacious against these worms may produce side effects that cause extreme discomfort. Here, Elizabeth Vande Waa describes the quest for new chemotherapeutic approaches for the treatment of filarial infections.

Onchocerciasis in Zaïre

The first mention in Africa of ocular lesions and of blindness due to onchocerciasis was made by Hissette in Zaïre in 1931, although the disease had already been known there since 1903. On a map of Zaïre were indicated all the known data of the geographical distribution of onchocerciasis: data from the literature, from field work and from the patients seen in Kinshasa. An estimation of the relative incidence of the disease was made by comparing the number of patients with the number of the latest population census for each administrative zone. The environmental and developmental factors determining the epidemiological aspects are discussed. The clinical aspects of the typical eye symptoms are reviewed. Their correlation with age, with immunology and with some specialized eye examinations are discussed.