Onchocerciasis treatment reduces prevalence and intensity by 38%

Onchocerciasis, river blindness or craw craw is an endemic disease in Bioko Island, Equatorial Guinea.

This pathology causes a weakening in affected individuals, most of them within the labour force population, making this disease one of the limiting factors for the economic development of the island. Onchocerciasis is caused by the worm Onchocerca volvulus. It is transmitted through the bite of the black fly, Simulium. Enviromental conditions such as humidity, rapid water rivers and altitude of Bioko favour the development of this pathology, since this is the habitat of the fly acting as a vector. The parasite, in the form of larve, is inoculated to humans when the fly bites humans to obtain blood. Female parasites measure 30 to 50 cm and live 10 to 15 years, whereas male parasites measure 3 to 5 cm. Worms form tumours in infected indivuduals, and some of them are easily visible. Fecunded females emit daily 1,200 larves (microfilaria) measuring 150-360 micras, which are disseminated through the host’s skin, eyes and other organs. Affected individuals can host 50-200 million worms, especially distributed in skin and eyes, usually provoking blindness.

The work, carried out by the group of Hospital Clinic de Barcelona, was led by Dr. Jordi Mas of the Microbiology Unit of Hospital Clinic-Universitat de Barcelona, and Dr. Carlos Ascaso of the IDIBAPS Epidemiology and International Health Research Group. The objective of this study was to assess the impact of 8-year vertical distribution of Ivermectin, the only treatment available against onchocerciasis, among the rural population of 12 communities and two ethnical groups: the Bubis and the Fangs. The fact that the administered drug dose is only effective on larves, conditions the duration of this study. The study was carried out during 8 years, because this is precisely the maximum time of fertility of females, what guarantees the total elimination of the offspring.

This study, published in Tropical Medicine and International Health, has been financed by the Spanish Agency of International Cooperation, and the World Health Organisation (WHO). It continues from the achievements of previous works held in Africa in order to assess Ivermectin effects and to determine the importance of onchocerciasis. Results are highly conclusive in this case: onchocerciasis prevalence before treatment was of 74.5%, and after treatment, 38.4%. Furthermore, we want to underline that after Ivermectin administration, the incidence of onchocerciasis in children aged 0-4 decreased 2.6 times.

The follow-up of this project creeted more than a decade ago by Dr. Jordi Mas continues to be in force by the Ministry of Health of Equatorial Guinea. Nevertheless, the monitoring of the state of the disease is conducted by the Catalan group from Barcelona and Bioko.

Future strategies of the fight against river blindness go further than the administration of Ivermectin. Currently, the vector of the disease is being eliminated by the WHO African Programme for Onchocerciasis (APOC). Dr. Jordi Mas will soon travel to Bioko in order to test the effects of the new measures. The efficiency of these methods, the operation of the project, along with the results of the studies of the Hospital Clinic Group will be assessed in the near future in a joint meeting with the Ministry of Health of Equatorial Guinea, the WHO and Dr. Jordi Mas.

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