Hope for River Blindness

Hope for River Blindness

by John Kiwanuka Ssemakula, 27 March 2002

A breakthrough in new research into Onchocerciasis (River Blindness) has brought New Hope to millions of sufferers of the debilitating disease. The breakthrough discovered by Eric Pearlman and co-researchers at Case Western Reserve University, Ohio suggests that the bacteria Wolbachia that is carried in the parasitic worms that infect people is responsible for triggering the immune response that causes the terrible symptoms of river blindness. The researchers found that the bacteria are susceptible to Doxycycline, a common antibiotic and can be killed in people infected with the worms.

River blindness is transmitted by the bite of the black fly (Simulium damnosum) which is infected with the parasitic worm Onchocerca volvulus. The worm then tunnels through the persons skin into the tissues where they can live for up to 14 years. During this time they reproduce releasing millions of microfilariae (microscopic larvae) that migrate throughout the body. When the microfilariae die they cause a massive inflammatory immune response that leads to visual impairment including blindness, rashes, lesions, intense skin itching and elephantiasis of the groin.

Currently the only safe treatment is a drug called Ivermectin produced in the 1980's, which is capable of killing the immature larval worms but only decreases the parasitic load without killing the mature worms and thus requires repeated doses of treatment.

Latest developments
Recent research has indicated the bacteria Wolbachia carried inside the parasitic worms are in some way essential for proper growth of the larval worms. In their research, Eric Pearlman and colleagues at Case Western Reserve University infected two groups of lab mice with extracts from the parasitic worm. One group was infected with worm extracts that had been treated with the antibiotic Doxycycline; the other group was infected with an untreated worm extract.

The mice infected with the treated worm extract were found to exhibit fewer symptoms than the group that had received the untreated extract with "live" bacteria. This seems to suggest that the bacteria are responsible for triggering the immune response in humans.

Implications
The research raises the possibility that sterilizing mature worms in infected people can lead to a reduction in the spread of the disease, by decreasing the numbers of infected hosts. However this does not mean the treated persons will be completely free from risk of contracting the disease again. They will still be susceptible to re-infection from the bites of infected flies with active parasites. A comprehensive control programme that includes elimination of the black fly is required to completely remove the risk of re-infection.

Current Control efforts
The WHO is currently coordinating a control programme based on breaking the parasitic cycle of transmission by eliminating the black fly through the aerial use of insecticides. The hypothesis is that by interrupting the cycle of River Blindness for 14 years, the reservoir of adult worms dies out in the host human population.

To complement the insecticide spraying campaign, since 1987 the WHO have initiated a campaign of distribution Ivermectin (provided by Merck at no cost at all) to selected population as a means of further reducing the transmission of the disease.

The latest findings offer a promising addition in the fight against River blindness, by permitting an even more comprehensive approach aimed at all the different segments of the parasitic cycle:

Reducing or eliminating the vector:

·Aerial insecticide spraying campaign to reduce or eliminate the black fly that transmits the parasitic worms

Reducing the reservoir of hosts:

· Killing the Wolbachia, the bacteria that infects the parasitic worms and causes the symptoms of the disease can be killed in infected people with Doxcycline, thus sterilizing the adult worms and decreasing the chances of further transmission of disease by black flies that bite an infected host.

· Killing the immature larval forms of Onchocerca Volvulus, the parasitic worm with Ivermectin thereby reducing the parasitic load in the host and ultimately reducing the host reservoir.

Onchcoerciasis Control Programme (OCP)
The OCP launched in 1974 was the first major programme developed to control onchocerciasis. By 1986 the programme covered 11 countries with a combined population of about 30 million people. The programme has been jointly sponsored by WHO, the World Bank, the UNDP and FAO. The programme proved very successful.

At OCP's launch, more than 1 million people in West Africa suffered from onchocerciasis, Today, the number of infected people within the original area of operations is practically nil. 25 million hectares of fertile riverine land that was previously deserted has been opened up for resettlement and cultivation,

Africa Programme for Onchocerciasis Control (APOC)
The success of the OCP led to the African Programme for Onchocerciasis Control (APOC) in December 1995. APOC’s objective is to establish sustainable community-directed ivermectin distribution systems covering about 50 million people in 19 countries where onchocerciasis still is a serious public health problem.