The burden of malaria in Africa.

PIP: Malaria remains one of the most serious public health problems in Africa, causing high morbidity and mortality. In highly endemic areas, malaria is responsible for about 30-50% of fever cases, 30% of outpatient consultations, and 10-15% of hospital admissions. Globally, about 1.5-2.7 million persons die from malaria yearly. Children under 5 years and pregnant women are the most vulnerable groups. Anaemia is one of the most serious consequences of malaria in young children in Africa, particularly in the countries where a high level of chloroquine resistance exists. In some zones, the temporary decline in transmissions due to climatic and ecological changes has altered the immunological profile of the population, resulting in serious outbreaks of epidemics accompanied by high morbidity and mortality. The African region has been experiencing malaria epidemics, with an unacceptably high disease burden and high mortality in the epidemic-prone areas in East and Southern Africa. In Botswana, for example, the incidence of malaria increased by 13.5 times in the Nata clinic during the 10th week of 1996, compared with the same period in 1995. WHO provided technical support and antimalarial drugs to the countries affected by these epidemics. This was followed by two workshops on epidemic prevention and control. The problem of drug resistance, which has been present in Africa for over 17 years, is more intense in East Africa. The approach of WHO/AFRO to this problem is to build capacities, within the health ministries of member countries, for antimalarial drug sensitivity testing and rational drug policies. In addition, WHO has developed a simple therapeutic efficacy test. It is proposed that this method be used by all countries of the region. This will make it easy to compare data and create a regional sensitivity picture.^ieng

Impact of combined large-scale ivermectin distribution and vector control on transmission of Onchocerca volvulus in the Niger basin, Guinea.

As part of the WHO Onchocerciasis Control Programme in West Africa (OCP), the attack phase of operations in the Niger basin in Guinea began in 1989 with the simultaneous use of ivermectin and vector control. Larvicide applications coupled with annual large-scale ivermectin distribution have greatly reduced blackfly infectivity (by 78.8% for the number of infective larvae per 1000 parous flies). The combination of vector control and ivermectin has permitted excellent control of transmission. In the original OCP area, it took 6-8 years of vector control alone to obtain an equivalent decrease in blackfly infectivity. For the same number of flies caught, transmission was much higher in areas where ivermectin had not been distributed. The combined use of ivermectin and vector control has opened up new prospects for carrying out OCP operations with, notably, the possibility of reducing larviciding operations.

PIP: As part of the World Health Organization Onchocerciasis Control Programme in West Africa (OCP), the attack phase of operations in the Niger basin in Guinea began in 1989 with the simultaneous use of ivermectin and vector control. All the 16 catching points were in holoendemic foci: 8 in the Niger basin in Guinea and 8 in the original OCP area (Mali, Ivory Coast, Ghana, and Burkina Faso). The data were analyzed according to prevalence of microfilariae in the skin and the mean community microfilarial load (CMFL). Between 1990 and 1992 the number of people in the villages treated increased by a factor of 6. In 1992 a total of 91,840 persons were treated in 550 villages. The study covered 10 years, during which 34,492 blackflies were caught at the 8 sites, 87.8% of which were parous. Larvicide applications coupled with annual large-scale ivermectin distribution had greatly reduced blackfly infectivity (by 78.8% for the number of infective larvae per 1000 parous flies; the number infective larvae in the head fell by 75.7% compared with the 1986-87 data before treatment began). After 2 years of large-scale ivermectin treatment, the reduction was 64.6%. In February and March of 1992 a defective larvicide worsened the situation. The average transmission potential during this period in Guinea was 7.3 compared with 93.7 for the original area. For the same number of blackflies caught, transmission in the original area was 5.6 times higher. The combination of vector control and ivermectin permitted excellent control of transmission. In the original OCP area, it took 6-8 years of vector control alone to obtain an equivalent decrease in blackfly infectivity. For the same number of flies caught, transmission was much higher in areas where ivermectin had not been distributed. The combined use of ivermectin and vector control has opened up new prospects for carrying out OCP operations with the possibility of reducing larviciding operations.

[Control of onchocerciasis vectors in West Africa: description of the logistics adapted for a large-scale public health program]. / La lutte contre les vecteurs de l'onchocercose en Afrique de l'Ouest: description d'une logistique adaptée a un programme de santé publique de grande envergure.

The Onchocerciasis Control Programme (OCP) in West Africa, launched in 1974, includes 11 participating countries and covers more than one million square kilometres. The aim of the OCP is to control blinding onchocerciasis (river blindness) which is caused by the savannah strain of Onchocerca volvulus transmitted by the Simulium damnosum complex. There is no effective macrofilaricide, so vector control to prevent the transmission of the parasite remains the method of choice, despite the availability of ivermectin, a drug which controls ocular morbidity. The potential value of vector control has been demonstrated by the original programme: 14 years activity has eliminated the disease as a public health problem in the areas included. This strategy requires adapted logistical support involving (i) widespread insecticide coverage (27,000 km of river are treated by the OCP during the rainy season), (ii) frequent (weekly) application of larvicide and (iii) prolonged intervention due to the life-span of the worm in the human reservoir, estimated to be approximately 14 years. We describe the vector control operations and their organisation 20 years after the initiation of the OCP. The OCP can be divided into 5 areas of logistic activity. The first covers activities involving insecticide and fuel management for the OCP as a whole: assessment of the requirements for the following year, ordering from insecticide and petrol suppliers, stocking fuel and insecticide at the depots covering the area. The second activity is the treatment of rivers with insecticide. This includes treating the ground with larvicide, the aerial operations run by an independent company supplying 12 helicopters on contract to the OCP, and use of satellite beacons for retransmitting of hydrological data. The third activity is monitoring the impact of larvicides on both the target (adult and larval S. damnosum) and on other fauna (fish, crustaceans and other insects). The fourth activity is field data collection and its processing. This involves a data transmission network to facilitate stock management insecticide application and entomological and hydrological surveillance using computer systems. The fifth activity is the coordination of vector control operations, technical and administrative staff and estimations of the funds available to the Vector Control Unit. The logistic aspects of other large-scale-insect-control programmes world-wide are considered, and the possibility of using the OCP as a model for such programmes (both public health and agricultural) is assessed.

The impact of five years of annual ivermectin treatment on skin microfilarial loads in the onchocerciasis focus of Asubende, Ghana.

Following the registration of ivermectin (Mectizan) for human use in the treatment of onchocerciasis, in 1987 the Onchocerciasis Control Programme in West Africa (OCP) begun a series of trials in order to determine the safety of the drug when used on a large scale and its potential for morbidity control. This paper reports the changes in skin microfilarial loads during the first 5 years of annual treatment in the holoendemic focus of Asubende in Ghana, which was the largest trial area and which also had the longest series of follow-up surveys. The general observed pattern was a marked reduction of microfilarial loads shortly after each treatment followed by a steady repopulation of the skin until a subsequent treatment round. The overall reduction of microfilarial loads observed between the base line survey and one year after the last treatment was 90% for the total population examined and over 93% for a cohort which received the drug at all 5 treatment rounds. In contrast, there was only a very gradual decrease in the prevalence of infection in the population after subsequent treatments. The study further emphasizes that even a single treatment with ivermectin has a significant medium-term impact on microfilarial loads. Microfilarial counts barely increased after 14-16 months of treatment and stabilized around 55% of pre-treatment counts 2-4 years after a single treatment.

[National entomological teams of the western extension zone of the Onchocerciasis Control Program (OCP) in west Africa from 1986 to 1990]. / Equipes nationales entomologiques de la zone d'extension ouest du programme de lutte contre l'onchocercose en Afrique de l'ouest (OCP) de 1986 à 1990.

The western extension area of the Onchocerciasis Control Programme in West Africa (OCP) covers five countries: Guinea, Guinea-Bissau, Mali (western part), Senegal and Sierra Leone. From 1986 to 1990, national teams employed by the respective governments have been regularly collecting entomological data on the vectors of onchocerciasis in these countries. As in the initial programme area of the OCP, the entomological surveillance network was composed of entomological sectors and subsectors (the latter are called "operational bases" in the western extension). In 1990, 308 staff in 47 capture teams were employed for the entomological surveillance activities in seven sectors and twenty-five operational bases. They included a national coordinator as head of the teams for each country, a wide range of technicians, and administrative support staff to assist the national coordinator in the overall management of available resources. The national teams worked under the technical responsibility and supervision of WHO/OCP but with no employee/employer relationship between them and WHO, since they were employed and their salaries were paid by their governments. The OCP, however, paid additional lump sum allowances to each worker, as well as daily subsistence allowances when away from their duty station. Vehicles, entomological equipment, office supplies and furniture, fuel and lubricants were provided by WHO/OCP. Despite the difficulties encountered in the field, which were often great, and their lower salaries (compared with colleagues paid by WHO/OCP), the technical workers in the national teams performed well by OCP standards, with results as satisfactory as those obtained by the WHO/OCP teams in the rest of the programme area. The main reasons for the efficiency and dynamism of the national entomological teams are described. The future of these teams after OCP has ceased its activities is also discussed.

Large scale ivermectin distribution and its epidemiological consequences.

Community trials were started to address questions concerning the safety of ivermectin during large scale treatment, its potential for transmission control, its effect in preventing ocular onchocercal disease, its acceptability and the organization of large scale treatment. A summary is presented of the major, latest results on the short-term epidemiological impact of large scale ivermectin treatment, as observed in eight community trials undertaken in the Onchocerciasis Control Programme in West Africa (OCP). Ivermectin treatment resulted in a 96%-99% reduction in the mean load of microfilariae (mf) in the skin in treated patients. The subsequent mf-repopulation of the skin was faster than in the clinical trials and after 12 months the mean loads had returned to more than 40% of the pre-treatment load. Ocular mf loads were also greatly reduced and a post-treatment regression of early lesions of the anterior segment of the eye was observed. The transmission of Onchocerca volvulus was reduced by some 60% during the first year after treatment in one trial but no additional reduction was observed after the second treatment round. These results, and other recent research findings, have been used to quantify an epidemiological model for the transmission and control of onchocerciasis. Preliminary results of computer simulations of the predicted long-term epidemiological impact of large scale ivermectin treatment indicate that ivermectin treatment may play a very important role in disease control but that it is unlikely to become a practical tool for transmission control in endemic foci. Ivermectin treatment appears to be the most appropriate method for control of recrudescence of infection in an area where the parasite reservoir has been virtually eliminated by vector control, such as in the core area of the OCP.

Onchocerciasis control programme-The human perspective.

The West African Onchocerciasis Control Programme (OCP), launched in 1974, seeks to interrupt transmission o f Onchocerca volvulus (Fig. I) over a vast area now encompassing 11 countries. The main strategy has been vector control using larvicides (particularly temephos) against blockfly larvae in fast-flowing rivers and streams. More recently, the programme has also begun to implement large-scale chemotherapy using ivermectin. The OCP has an operational budget approaching US$25 million a year. The control activities have led to a dramatic decrease in the incidence of new cases, while overall prevalence of infection has been reduced from about 25-30% to below 5%, accomponied by a similar drop in the numbers o f people presenting severe ocular involvement or blindness. Entomological, clinical and epidemiological results of the programme have been discussed in detail -particularly in the various reports produced by programme personnel and associated researchers (eg. Ref. I). Here, we asked James Senghor and Ebrohim Samba to discuss what the programme has meant to the people involved.

Yellow fever in the Gambia, 1978--1979: epidemiologic aspects with observations on the occurrence of orungo virus infections.

An epidemic of yellow fever (YF) occurred in the Gambia between May 1978 and January 1979. Retrospective case-finding methods and active surveillance led to the identification of 271 clinically suspected cases. A confirmatory or presumptive laboratory diagnosis was established in 94 cases. The earliest serologically documented case occurred in June 1978, at the extreme east of the Gambia. Small numbers of cases occurred in August and September. The epidemic peaked in October, and cases continued to occur at a diminishing rate through January, when a mass vaccination campaign was completed. The outbreak was largely confined to the eastern half of the country (MacCarthy Island and Upper River Divisions). In nine survey villages in this area (total population 1,531) the attack rate was 2.6--4.4%, with a mortality rate of 0.8%, and a case fatality rate of 19.4%. If these villages are representative of the total affected region, there may have been as many as 8,400 cases and 1,600 deaths during the outbreak. The disease incidence was highest in the 0- to 9-year age group (6.7%) and decreased with advancing age to 1.7% in persons over 40 years. Overall, 32.6% of survey village inhabitants had YF complement-fixing (CF) antibodies. The prevalence of antibody patterns indicating primary YF infection decreased with age, in concert with disease incidence. The overall inapparent:apparent infection ratio was 12:1. In persons with serological responses indicating flaviviral superinfection, the inapparent:apparent infection ratio was 10 times higher than in persons with primary YF infection. Sylvatic vectors of YF virus, principally Aedes furcifer-taylori and Ae. luteocephalus are believed to have been responsible for transmission, at least at the beginning of the outbreak. Eighty-four percent of wild monkeys shot in January 1979 had YF neutralizing antibodies, and 32% had CF antibodies. Domestic Aedes aegypti were absent or present at very low indices in many severely affected villages (see companion paper). In January, however, aegypti-borne YF 2.5 months into the dry season was documented by isolation of YF virus from a sick man and from this vector species in the absence of sylvatic vectors. Thus, in villages where the classical urban vector was abundant, interhuman transmission by Ae. aegypti occurred and continued into the dry season. A mass vaccination campaign, begun in December, was completed on 25 January, with over 95% coverage of the Gambian population. A seroconversion rate of 93% was determined in a group of vaccinees. This outbreak emphasizes the continuing public health importance of YF in West Africa and points out the need for inclusion of 17D YF vaccination in future programs of multiple immunication.