- Introduction
Onchocerciasis, or more commonly called as river blindness, is a parasitic disease, in which the parasite breeds in water. The organism causing the disease, Onchocerca volvulus, is a thin worm that can live for up to 14 years in the human body. The disease is transmitted from one person to another by the bite of a blackfly vector (WHO, 2001).
It is a debilitating skin disease particularly prevalent in poor and rural African countries. The affected person has severe itching. It affects the eyes too resulting in blindness. Blackflies, which transmit the disease from person to person, deposit infected larvae in an individual’s skin, which further grows into worms (WHO, 2009).
According to report published by the WHO in 2001, river blindness had affected 18 million people worldwide and was the world’s second leading infectious cause of blindness. Its prevalence is mostly in African countries, particularly some 36 countries of Africa, and also some parts of Central and Latin America, as well as the Arabian Peninsula (WHO, 2001).
As per a report published by the WHO in July 2009, 37 million people have been affected, which shows the number of affected people is constantly growing, in spite of many measures taken to control it (WHO, 2009).
- Life cycle of the organism
The parasite is transmitted to humans by the blackfly vector of Simulium species carrying infectious third-stage larvae (Globisch, 2013). The worms have a lengthier life. Inside the human body, the male and female worm parasites entangle with each other in the form of nodules in the subcutaneous tissue of the human skin. After mating, the female worms release around 1000 microfilariae larvae a day into the surrounding tissue, which can live for one to two years moving around inside the body of the host (APOC, Life-cycle of Onchocerca volvulus, WHO, n.d.). When they die, they cause an inflammatory response that leads to skin rashes followed by intense itching and lesions, and also leading to depigmentation of the skin. Microfilariae also migrate to the eyes, where they cause inflammation and other complications that can ultimately lead to blindness (APOC, Life-cycle of Onchocerca volvulus, WHO, n.d).
- The blackfly vector
Blackflies breed in water particularly, fast-flowing rivers and streams, increasing the risk of infection to people living in the surrounding areas. When a female blackfly bites an infected person for its meal, the parasite is transferred from the person to the fly and from the fly to another person (APOC, Life-cycle of Onchocerca volvulus, WHO, n.d). The parasite can survive in the body of the fly too and over a course of just one to three weeks, they develop inside the blackfly to form infective larvae. These are then passed on to other humans when the blackfly feeds itself on another person’s blood meal. Once in the human body, the larvae form nodules which mature into adult worms, completing the cycle (APOC, Life-cycle of Onchocerca volvulus, WHO, n.d).
- Economic burden of the disease
River blindness is a major cause of blindness in the affected areas; therefore it has also affected the economic growth of these areas. The economic productivity is greatly reduced and has left a large amount of fertile land totally abandoned. It is estimated that there are about half a million blind people in the world only due to the infection with the parasite, Onchocerca volvulus (Priority Eye Disease, WHO, n.d.).
When the Onchocerciasis Control Programme in West Africa (OCP) was closed successfully in December 2002, the achievements were many. A total of eighteen million children were born in areas free from the risk of blindness, nearly about six million cases of blindness were prevented, and 25 million hectares of land was announced safe for resettlement, something which is significantly reducing the economic impact on the region (Basanez et al, 2006).
- Measures for vector elimination
Global initiatives to control the disease have begun already from 1974 with effective vector control being implemented in West Africa. In 1992, a Non-Governmental Development Organization group was formed to help promote worldwide interest and support the use of a drug, ivermectin, in endemic countries to eliminate onchocerciasis as a public health problem (Priority Eye Disease, WHO, n.d). Since 1996, ivermectin was introduced by the African Programme for Onchocerciasis Control (APOC) in many African countries and by the Onchocerciasis Elimination Programme in the Americas (OEPA) in the affected Latin American countries (Priority Eye Disease, WHO, n.d).
In Uganda, the United Republic of Tanzania, and Equatorial Guinea, there are four areas where community treatment for the disease has been supplemented with an objective to eliminate the blackfly vector (APOC, Vector Elimination, WHO, n.d). In some APOC countries, vector control did not seem to be feasible or cost-effective, but in these four isolated regions, vector elimination targets are realistic. In these four regions, ground larviciding activities using environmentally safe insecticides continued for two to three years continuously and were completed in 2005. APOC is now monitoring these areas and providing support for entomological surveillance to confirm the elimination of the vector (APOC, Vector Elimination, WHO, n.d.).
- Drug therapy
Treating large masses of population is at the heart of APOC’s work to eliminate onchocerciasis. In the rural and poor areas of sub-Saharan Africa where health systems and health resources are little, the mass - directed treatment strategy with ivermectin is proving to be successful in reducing the disease burden (CDTI, APOC, WHO, n.d.).
Ivermectin is given once a year to people in the parasite-endemic areas to kill the larvae causing the disease. As per WHO, the treatment has been very effective in controlling the disease. A pharmaceutical giant, Merck and Co. has been donating ivermectin free of charge to affected African communities (WHO, 2009). However, treatment needs to be given annually and if it is stopped, the new larvae will begin to form. Interestingly, the Public Library of Science Journal on Neglected Tropical Diseases has published a study that has shown that after a longer period of time, i.e., almost after fifteen to seventeen years of treatment with ivermectin, the new larvae production can stop and even after two years after the last treatment with ivermectin, there were no signs of infected people (WHO, 2009).
Another promising drug in pipeline is moxidectin that is been studied to either kill the larvae or sterilize them. It is studied to be given just for 5 to 6 years, unlike ivermectin which has to be given for 15 to 17 years (WHO, 2009).
According to a very recent review by Globisch, ivermectin has definitely controlled transmission of the microfilariae, with an African Program elimination target date of 2025 (Globisch et al, 2013). However, there is currently no point-of-care diagnostic that can distinguish the burden of the disease - including active and/or past infection—and enable the elimination program to be effectively monitored (Globisch et al, 2013).
References:
World Health Organisation. Water-related Health. Water Sanitation Health. 2001. Accessed: 14th March 2013; Retrieved: http://www.who.int/water_sanitation_health/diseases/oncho/en/
World Health Organisation. Progress to help eliminate river blindness. 2009. Accessed: 14th March 2013; Retrieved: http://www.who.int/mediacentre/multimedia/podcasts/2009/river_blindness_20090722/en/index.html
Globisch D, et al. “Onchocerca volvulus-neurotransmitter tyramine is a biomarker for river blindness.” PNAS (February 2013)
World Health Organisation. Life-cycle of Onchocerca volvulus. African Programme for Onchocerciasis Control (APOC).n.d. Accessed: 14th March, 2013. Retrieved: http://www.who.int/apoc/onchocerciasis/lifecycle/en/index.html
World Health Organisation. Priority eye diseases. Prevention of Blindness and Visual Impairment. 2013. Accessed: 14th March, 2013 Retrieved from: http://www.who.int/blindness/causes/priority/en/index3.html
Basáñez MG, et al. “River blindness: a success story under threat?” PLoS Med. 3 (September 2006): e371.
World Health Organisation. Vector elimination. African Programme for Onchocerciasis Control (APOC). Accessed: 14th March, 2013; Retreived: http://www.who.int/apoc/vector/en/
World Health Organisation. Priority eye diseases. Prevention of Blindness and Visual Impairment. 2013. Accessed: 13th March, 2013; Retrieved: http://www.who.int/blindness/causes/priority/en/index3.html
World Health Organisation. Vector elimination. African Programme for Onchocerciasis Control (APOC). n.d. Retreived from: http://www.who.int/apoc/vector/en/
World Health Organisation. Community-directed treatment with ivermectin (CDTI). African Programme for Onchocerciasis Control (APOC). N.d. Accessed: 14th March 2013; Retrieved: http://www.who.int/apoc/cdti/en/
