Onchocerciasis in the Benue State of Nigeria. II. Prevalence of the disease among the Tivs living in the Kwande Local Government area

The geographic distribution of onchocerciasis in the 20 participating countries of the African Programme for Onchocerciasis Control: (1) priority areas for ivermectin treatment

Background

The African Programme for Onchocerciasis Control (APOC) was created to control onchocerciasis as a public health problem in 20 African countries. Its main strategy is community directed treatment with ivermectin. In order to identify all high risk areas where ivermectin treatment was needed, APOC used Rapid Epidemiological Mapping of Onchocerciasis (REMO). REMO has now been virtually completed and we report the results in two articles. The present article reports the mapping of high risk areas where onchocerciasis was a public health problem. The companion article reports the results of a geostatistical analysis of the REMO data to map endemicity levels and estimate the number infected.

Methods

REMO consists of three stages: exclusion of areas that are unsuitable for the vector, selection of sample villages to be surveyed in each river basin, and examination of 30 to 50 adults for the presence of palpable onchocercal nodules in each selected village. The survey results and other relevant information were processed in a geographical information system. A panel of experts interpreted the data taking the river-based sampling into account and delineated high risk areas where the prevalence of nodules is greater than 20%.

Results

Unsuitable areas were identified in eight countries. In the remaining areas surveys were done in a total of 14,473 sample villages in which more than half a million people were examined. High-risk areas were identified in 18 APOC countries, ranging from small isolated foci to a vast contiguous endemic area of 2 million km² running across seven countries. In five countries the high risk area covered more than 48% of the total surface area, and 31% to 48% of the population. It is estimated that 86 million people live in high risk areas in the APOC countries.

Conclusions

The REMO maps have played a significant role in onchocerciasis control in the 20 APOC countries. All high-risk areas where onchocerciasis used to be a serious public health problem have been clearly delineated. This led to the creation of community-directed treatment projects that by 2012 were providing annual ivermectin treatment to over 80 million people.

Onchocerciasis in Taraba State, Nigeria: clinical-epidemiological study of at-risk males in Bakundi District

An epidemiological study of 1366 adult males from fourteen communities of Bakundi district of Taraba State, Nigeria was carried out to establish the prevalence and intensity of onchocerciasis. The findings of the study showed that 45.2% of subjects were infected. Ten communities had infection rates in excess of 30%. Lizard skin and leopard skin were seen in 3.5% and 2.0%, respectively, and increased with increasing age. Hanging groin (2.6%) and scrotal enlargement (8.6%) were also observed. There was a good correlation between the infection rate on one hand and the presence of nodules (r = 0.85, P < 0.05), hanging groin (r = 0.56, P < 0.05) and scrotal enlargement (r = 0.62, P < 0.05) on the other. There was also a significant correlation between the intensity of infection on the one hand and lizard skin (r = 0.67, P < 0.05), leopard skin (r = 0.88, P < 0.05) and hanging groin (r = 0.82, P < 0.05) on the other. Those who worked in the fields (such as hunters, farmers and fishermen) had higher infection than others because of frequent contact with the vector. Extensive surveys of all suspected river valleys must be carried out to identify all those communities which will benefit from ivermectin treatment.

Forest onchocerciasis in Cameroon: its distribution and implications for selection of communities for control programmes

The prevalence of infection and disease due to Onchocerca volvulus in regions at different altitudes and distances from the nearest breeding site for the Simulium vectors were studied in a forested area of Cameroon. A total of 1,785 subjects in 14 villages underwent clinical and parasitological evaluation. According to WHO endemicity criteria, villages 267 and 720 m above the sea level (asl) were hyperendemic, whereas lower villages, at 55 n asl, were meso-endemic. Altitude was positively correlated and distance from vector breeding site negatively correlated with several clinical indicators of onchocerciasis: prevalence of infection, microfilarial density, onchocercomata, and blindness. Location and altitude of his or her village and the subject's duration of residence in the village, age and sex were all found to be independent predictors of infection by logistic regression. The observed pattern of forest onchocerciasis reflects an interplay of multiple factors rather than a simple relationship between endemicity and distance from the nearest river. In order to select communities most affected by onchocerciasis for control programmes, two indicators, the prevalence of blindness and the prevalence of onchocercomata, might be used.

Onchocerciasis and women's reproductive health: indigenous and biomedical concepts

Women in a rural farming community in Etteh, Nigeria, have traditional beliefs about onchocerciasis which differ from the concepts of modern science. Recognizing these beliefs may allow health workers to gain the confidence and participation of the people and increase the effectiveness of control programmes.

Preliminary observations on the distribution of ivermectin in Nigeria for control of river blindness

A total of 118,925 individuals in four Nigerian states was treated for onchocerciasis between February and December, 1991, using centralized and house-to-house distribution of ivermectin. Pre-treatment prevalences of the disease ranged between 28% and 90%. Only 0.7% of those treated reported adverse reactions within three days of treatment: 230 individuals (0.19%) had headache, 210 (0.17%) general body pains, 150 (0.12%) pruritus, 120 (0.10%) oedema, 80 (0.06%) fever, 20 (0.02%) dizziness, 15 (0.01%) vomiting, 10 (0.01%) diarrhoea, and 25 individuals (0.02%) noticed that they passed intestinal worms. Treatment in the endemic communities continues. The results show that mass treatment of onchocerciasis with ivermectin is quite safe and the drug's acceptability increases its potential as the drug of choice for control of onchocerciasis in Nigeria.

Filariasis in the Igwun River Basin, Nigeria: an epidemiological and clinical study with a note on the vectors

In a cross-sectional, epidemiological and parasitological study of human filariasis, 845 individuals were examined in settlements along the Igwun Basin, Imo State, Nigeria. Four different filarial nematode species were identified. Two hundred and fifty-six (30.3%) of the individuals examined were positive for Onchocerca volvulus, 113 (13.4%) for Mansonella perstans, 76 (9.6%) for Wuchereria bancrofti and 77 (9.1%) for Loa loa. Microfilarial rates increased with age of individuals and showed a tendency towards higher prevalence rates in males than in females. The intensity of O. volvulus infection was high, with the highest microfilarial density of 44 mf mg-1 snip which occurred in the 40-49-year-old individuals. In W. bancrofti and L. loa infections, infections of over 1000 mf 20 ml-1 blood were recorded in 15.8% and 19.5% of individuals, respectively. Observed clinical signs were associated with inflammatory, lympho-obstructive and ocular manifestations. In M. perstans infections all clinical cases were inflammatory. In W. bancrofti, 44.4% of clinical cases were inflammatory, and lympho-obstructive manifestations consisted of 23.8% chyluria, 12.7% hydrocele and 19.1% elephantiasis. In L. loa infections all clinical cases were inflammatory with indications of Calabar swellings. In O. volvulus infections 23.5% of clinical cases were inflammatory, while 76.5% showed ocular manifestations. The absence of blindness despite high O. volvulus infection rates was remarkable. The presence of potential insect vectors and the occurrence of clinical signs are indications of active transmissions.

Onchocerciasis in Plateau State of Nigeria. II. The prevalence among residents around the Assob River area

A study of the prevalence of human onchocerciasis in eight villages around the Assob River in Jos Plateau, Nigeria, was undertaken between October 1983 and March 1985 using the skin-snip method. A total of 1673 individuals were examined. One hundred and eighty five (11.06%) had microfilariae of Onchocerca volvulus in their skin biopsies, and of these infected people, five (2.7%) were blind. The highest prevalence rate recorded was in Ngwan Madaki, where 51 (26.3%) of the 194 people examined were infected. The lowest percentage prevalence was recorded in Dogon Fili with four (1.95%) of the 205 people examined being positive. The proportion of infected people increased with age; and onchocercal lesions were significantly more common in older than in younger persons (P less than 0.05). There was no significant difference between infection rates in males and females (P greater than 0.05), although the overall percentage infection and the numbers of onchocercal lesions were higher in males than in females.