Introduction

Onchocerciasis is an insidious nonfatal filarial disease that causes blindness, lifelong human suffering, and grave socioeconomic problems. It is a cause of clinical and epidemiological burden of skin disease in Africa. An estimated 40 million people are afflicted worldwide with about 2 million blind. About 85.5 million people in 35 countries live in endemic areas. It is endemic in 28 countries in Africa, 6 countries in the Americas, and in Yemen. Some 18 million people are estimated to be infected (over 99% of them living in Africa) (1). In 1875, O'Neill first reported the presence of filaria in “craw-craw” as onchocerciasis is called in West Africa. In 1919, Robles described in the French literature an anterior uveitis and keratitis associated with acute and chronic skin changes (1). Budden reported onchocerciasis as an important cause of blindness in many parts of Northern Nigeria (2,3).

Onchocerciasis, or river blindness, is caused by infection with the filarial parasite Onchocerca volvulus. The parasite is transmitted by Simulium species (blackflies) that breed in fast flowing streams (4,5). Until recently the blindness and skin pathology caused by heavy infections, constituted a major public health problem in many parts of tropical Africa, Yemen, and Latin America. In the West African savannah, the risk of onchocercal blindness used to be very high along the rivers, where the vector breeds, and blindness could affect up to 50% of adults in the most endemic communities. The fear of blindness resulted in depopulation of the fertile river valleys, and this made onchocerciasis a major obstacle to socio-economic development in West African savannah regions (1).The socio-economic importance of the disease was the main reason for creation of the Onchocerciasis Control Programme in West Africa (OCP) in 1975 (6) in West Africa, the Onchocerciasis Elimination Program in the Americas (OEPA) (7), and the African Program for Onchocerciasis Control (APOC) (8,9). All three programmes have come to rely on the regular (OEPA semi-annually, OCP both annually and semi-annually, and APOC annually) distribution of ivermectin (Mectizan®) to lower the microfilarial load in affected individuals and thereby reduce transmission and mitigate the clinical manifestations of the infection (10). In addition, since 1975, OCP has made intensive use of vector control by means of aerial larviciding. This has led to the virtual elimination of the parasite from many formerly endemic areas.

In most endemic parts of the world, onchocerciasis (river blindness) control relies, or will soon rely, exclusively on mass treatment with the microfilaricide ivermectin. Macrofilaricidal drugs are currently being developed for human use (11). Unfortunately, the number of safe effective alternative treatments is limited. Diethylcarbamazime, also a microfilaricide, causes severe side effects in onchocerciasis patients (12). Suramin, the only currently available highly effective macrofilaricide has even more serious side effects (13). Large scale nodulectomy, which has been attempted in Latin America, is impractical and will never succeed in eliminating all adult worms (14,15).

Some success was obtained with amocarzine, although its macrofilaricidal properties were not optimal (16). Several other compounds are currently under consideration. One of these is doxycycline which following long-term treatment was shown to sterilize adult worms in treated humans, an effect that was correlated with the disappearance of the filarial endosymbiont (Wolbachia spp) (17,18). Another promising drug, widely used in veterinary practice, is moxidectin (19,20). When used as a single dose it either kills or sterilizes the adult worm depending on the animal model and parasite used. The half-life of this drug in animals is approximately 10 times that of ivermectin, thereby reducing the probability of successful re-infection. However, the effect of this compound in humans remains to be evaluated.

More than 32 million Nigerians in 32 states and the Federal Capital Territory are estimated to be at risk for onchocerciasis. Nigeria accounts for nearly 40% of the world’s burden of onchocerciasis. Control efforts commenced in 1988 with prevalence surveys and pilot treatment project in Kwara state. Mass treatment with Ivermectin was initiated in 1991 and extended later to other endemic states with the assistance of UNICEF and other international organizations. And in 1997, Nigeria started receiving support from the African Programme for Onchocerciasis Control (APOC) and commenced usage of the Community Directed Treatment with Ivermectin (CDTI) or ComDT (a TDR product) a concept from Community Directed Intervention (CDI).APOC was set up in 1995 to establish within a period of 12 to 15 years, effective and sustainable, community-directed treatment with Ivermectin throughout the endemic areas within the geographic scope of the programme, and, if possible, to eradicate the vector in selected and isolated foci, by using environmentally safe methods. It targets by 2010 to treat 89,998,211 persons in 111 projects. In CDI health intervention is undertaken at the community level under the direction of the community itself of which the communities take charge of distributing health commodities themselves with guidance from the health service.

Methods

Demographic data on onchocerciasis treatment in Nigeria was compiled from 1991, on demographics (age, sex, community of residence), number of tablets of Mectizan used and Severe Adverse Events (SAEs). The data collected from 1991 through 2006 was based on standardized format which was sent to the local health department from the national office for use at the community for the compilation of data of people treated in the population based on census taken by the volunteers (Community Directed Distributors-CDDs) and was updated yearly.

To assess the trend, percentage therapeutic coverage was calculated for each year. For the combined trend (1991-2006) a 2-year interval starting 1991 through 2006 of the therapeutic coverage was used. Statistical tests for trend were performed by using the Cochrane-Armitage test (21). We tested for significance of the percentage therapeutic coverage ratios (PTRs) using a Poisson regression model.

Results

From 1991-1997 (the pre-APOC funding period) 2,392,554 people were treated on the average annually. During this 7-year period, the percentage national therapeutic coverage was very low but generally increased from 4% to 35% before dropping to 33% and then increased to 45% by 1997 (table 1). The mean therapeutic coverage was 18%. A significantly increasing trend (P<0.01) reaching a maximum of 45% in 1997 was observed (figure 1).

Figure 1

For the APOC funding period (1998-2006) 17,250,485 people were treated on the average annually. During this 10-year period, the percentage national therapeutic coverage also generally increased from 55% to 78% (table 3). The mean therapeutic coverage for the treatment was 72% for the period 1998-2007. A significantly increasing trend (P<0.01) reaching a maximum of 78% in 200 was observed (figure 2). The percentage therapeutic coverage for pre-APOC period (1991-1997) was 18% and for the APOC funding period it was 72% in Nigeria (PTRs 4, P<0.01).

During the pre-APOC period (1991-1997) the lowest national geographic coverage was 28% and it increased to 78% in 1997 with a mean of 48% (table 2). During this period, only Delta, Edo and Taraba States had records of the communities they were treating. Adamawa and Borno States had data for 1996 and 1997. However, Adamawa commenced treatment in 1992 while, Borno commenced in 1993. Cross River commenced in 1994 and Oyo in 1991, but they had community records for 1997 only. Bauchi, Benue, Kaduna and Niger commenced treatment in 1991 but do not have community records. Also Ondo, Osun and Plateau do not have community records but commenced treatment in 1992. Apart from Anambra, Enugu, FCT and Yobe that commenced in 1995, and Ebonyi, Nasarawa and Zamfara that commenced in 1997, all other states commenced in 1993 (table 3). The communities that were under treatment during the pre-APOC funding period (1991-1996) were 9535, while a total of 1933 communities were treated on the average annually.

Figure 2

The communities that were under treatment during APOC funding period and commencement of CDTI (1998-2006) were 39803, while a total of 29882 communities were treated on the average annually. Ebonyi, Enugu, FCT, Jigawa and Kogi states had 100% geographic coverage annually from 1998 to 2006. Anambra, Borno, Kano, Kebbi, Ondo, Osun, Sokoto and Zamfara states had 4 consecutive years of 100% geographic coverage respectively. Kebbi had 5 consecutive years of 100%. Yobe and Bauchi had 100% geographic coverage in all the years except 2000 and 2006 respectively. The average geographic coverage was highest in 2006 with 98%, followed by 2001, 2003 and 2004 with 95%. The mean geographic coverage was 92%. In 1998 to 2006 the performance of 6 projects in terms of geographic coverage was between 12-59%. These were Kano, Niger, Ondo, Osun, Oyo Adamawa, Borno and Ekiti states. Kano had 12% in 2000, and the next year 2001 the coverage went up to 100%, and this was maintained over the subsequent years. Niger state had 32% in 2000 and improved to 100% but dropped to 91 % in 2006. Ondo and Osun also recorded 47% and 42% respectively in 2000, but moved gradually to 100% which they maintained for the past 4 years. Adamawa moved from 29% in 1997 to 100% in 2001, but dropped in 2002, 2003, 2004, and moved up again to 100% in 2005 and 2006 (table 4).

For the trend for the 16 years (1991-2006) in terms of therapeutic coverage the mean was 51% (95% CL=47.6-54.4). A significantly increasing trend (P<0.01) reaching a maximum of 77% in 2006 was observed.

Discussion

Progress has been made in reaching the ultimate treatment goal in most countries, apart from Angola, Burundi, Central African Republic, Democratic Republic of the Congo and Sudan, where the therapeutic coverage is below the threshold of 65%, due mainly to political unrest. In 2006, all 13 foci in Latin America had reached a therapeutic coverage of at least 85% for the first time

For the pre-APOC (1991-1997) Plateau state started well in 1992 with a therapeutic coverage of 84% which increased to 100% in 1995 and 1996, but decreased to 86% in 1997. Edo State was next with 51% in 1993 but moved up to 60% in 1996 and decreased to 59% in 1997. The geographic coverage during this period was generally lower than what was achieved in the APOC funding period of 1998-2006 and it might be due to limited funding. The increase in funding by APOC and the use of CDTI strategy might be responsible for the increased therapeutic coverage.

In 1998 the states that achieved the minimum of 65% therapeutic coverage were 9 and it increased to 27 in 2006. In the same vein the states that achieved the maximum of 85% therapeutic coverage in 1998 were 2 and it increased to 10 in 2006. FCT performed well with an average therapeutic coverage of 87%. Sokoto State was next with therapeutic coverage of 86.7%.

There were variations in the total number of target communities reported over the years. This was due to several reasons among which are: merging and de-merging of communities, non coverage of CDTI area, reporting of communities treated passively as part of the target communities and poor census update. A drop in the total target communities in 2006 was recorded due to exclusion of communities in large urban areas where passive treatment were on in states like Oyo as well as the streamlining of communities being reported in Kano, Jigawa and Kwara States.

The country recorded progress towards improving therapeutic and geographic coverage, integration and co-implementation of Onchocerciasis and other disease control activities, while CDTI database was also developed.

So far, CDI has been effective in Nigeria. Ivermectin treatment is popular and communities have responded enthusiastically to the concept of community-directed treatment.

The recent external evaluation of APOC concluded that “ComDT has been a timely and innovative strategy ... communities have been deeply involved in their own health care on a massive scale … that ComDT is a strategy which could be used as a model in developing other community-based programmes and is also a potential entry point in the fight against other diseases”. There is a growing interest at the international and national level to use the ComDT model for interventions against other diseases (1).

Figure 3

Table 1: Percentage therapeutic coverage prior to APOC Funding

Figure 4

Table 2: Percentage geographic coverage prior to APOC Funding

Figure 5

Table 3: Percentage therapeutic coverage during APOC Funding

Figure 6

Table 4: Percentage geographic coverage during APOC Funding