The world inventory is dedicated to its original architect, roger w. They are found almost globally, from the tropics to the arctic tundra. To date, the number of flies attacking humans has only been determined by standard fly collectors near the river or the village. Black fly are true flies from the family simuliidae in the order diptera. This blindness had probably caused the extensive depopulation of fertile river valleys in northern ghana which so puzzled 19th century colonial administrators. Eggs require fastrunning rivers which have welloxygenated water for breeding grounds. The vectors of onchocerca volvulus are mainly simulium damnosum complex blackflies, but a species of the simulium neavei group may also. They belong to the suborder nematocera and family simuliidae, usually called black flies. Onchocerciasis, like most of the cyclically transmitted diseases, has a very high basic reproductive number ro. Hydroelectric dams can alter activity of black flies and may provide breeding sites for black fly. Pdf human onchocerciasis is a debilitating tropical infection that can result in blindness and severe skin disease. Members of the dipteran genus simulium are of significant medical and veterinary importance. There are at least 4 main subspecies found in the rainforest and savanna.
Seasonal variations in human onchocerciasis transmission. A comprehensive revision of the taxonomic and geographical inventory 2020 peter h. In africa the simulium damnosum complex are the most important vectors of onchocerciasis. Abu hamed, the northernmost onchocerciasis focus in the world, is located along the river nile banks in the nubian desert. Onchocerca volvulus, the causative agent of river blindness, is transmitted through the black fly simulium damnosum s. Simuliidae introduction distribution life cycle and description damage management selected references introduction back to top. Human onchocerciasis is an eye and skin disease caused by a filarial worm called onchocerca volvulus, which is transmitted by the bite of an infected black fly, of the genus simulium. A blackfly simuliumdamnosum under microscope x 100.
Onchocerciasis is caused by a nematode worm onchocerca volvulus, which is transmitted in sudan by black fly vectors of the simulium damnosum sensu lato species complex. These investigations showed that simulium damnosum is wide spread along the. Seven species belonging to three subgenera, eusimulium 1, gomphostilbia 1 and simulium 5 belonging genus simulium were encountered. Onchocerciasis, or river blindness, is a neglected tropical disease ntd caused by the parasitic worm onchocerca volvulus. Humans acquire onchocerciasis through the bite of simulium blackflies see image below. Merowe dam, the largest hydropower project in africa, was built west of abu hamed focus in 2009. Black flies are daytime biters preferring low wind conditions. A small and very pale species, only found in the sudan savanna. The status of onchocerciasis vectors in the former ruwenzori focus in western uganda was reexamined some 15 years after control measures against simulium damnosum s.
Onchocerciasis is a disease produced by the infection with the parasitic nematode o. An individual may acquire the disease if he is bitten by a black fly under the genus simulium carrying o. The impact of merowe dam on simulium hamedense vector of onchocerciasis in abu hamed focus northern sudan. Onchocerciasis river blindness clinical presentation. Onchocerciasis is an eye and skin infection caused by the parasitic worm, onchocerca volvulus, which is transmitted by the bite of an infective blackfly genus simulium. Florida occasionally experiences outbreaks of black flies, though this is a rare occurrence, and these large populations are caused by rainfall extremes. Preliminary investigations were carried out between the months of june 2008 and february 2009 to verify the transmission potentials of s. The disease is characterized by severe skin disease and blindness. In sudan, the disease is found in four foci where fast flowing rivers provide suitable breeding sites for the simulium vector flies. It is the secondmost common cause of blindness due to infection, after trachoma. Symptoms of onchocerciasis do not appear until after the l3 larvae mature into adult worms. The infection has caused blindness in 270 000 and left another 500 000 with severe visual impairment. Onchocerciasis or river blindness is a parasitic disease.
Simulium flies, while attempting to land on human were collected between 07. Light infectiom by the worm onchocerca voluulus leukart do not normally cause any grave symptoms, but heavy and repeated infections may lead to blindness caused by physical dam. The study was carried out for three months of the rainy season august, september and october, 1999 and three months in the dry season november, december, 1999 and. However, transmission patterns vary from one ecological zone to another and this may be due to differences in species of blackfly vectors and the climatic conditions in the area. Simulium venustum follows the trail of carbon dioxide and surveys the host to see if the host is suitable. The construction of dams and irrigation schemes for agricultural purposes has. As flies get within a few centimeters of the host, the fly senses heat expended by the host and lands on the area of exposed skin. Assessment methods while simulium flies were collected using human baits. Map showing the presences of onchocerciasis in nigeria source.
The two communities sampled were found to be endemic for onchocerciasis endemicity palpable nodules, skin depigmentation. The impact of the dam on onchocerciasis and its black fly vectors in abu. If a blackfly bites an infected person, onchocerciasis larvae can be ingested by the blackfly after which they migrate to the flight muscles. Simuliidae and the transmission and control of human. Examinations were completed in 1,455 participants from 11 onchocerciasis sentinel villages, and o. Onchocerciasis is associated with fast flowing rivers where simulium blackfly vectors breed. Full length research article onchocerciasis is transmitted to humans by the black fly, simulium damnosum. Simulium damnosum is the primary vector for the onchocerca volvulus filarial worm, or river blindness parasite that affects humans in africa.
Observations on seasonal variations in onchocerciasis transmission by simulium damnosum sensu lato were made in a study carried out in kwa falls, aningeje in akamkpa lga a typical forest area of cross river state, nigeria. Adult flies of this complex are black and are recognized by broad and flat front tarsi with a dorsal crest of tiny hairs, and by a broad white area on the first segment of the hind tarsus service 2008. It is common in tropical africa and central and south america. Mean monthly transmission potentials ranged from 104 in august to 5196 in february. Onchocerciasis university of california, riverside. Onchocerca volvulus infection and serological prevalence. The disease is called river blindness because the blackfly that transmits the infection lives and breeds near fastflowing streams and rivers, mostly near remote rural villages. A black fly or blackfly sometimes called a buffalo gnat, turkey gnat, or white socks is any member of the family simuliidae of the culicomorpha infraorder.
Nkpologu had a higher prevalence rate of nodules 5. Onchocerciasis usaids neglected tropical disease program. Controlling onchocerciasis river blindness in subsaharan africa. Knowledge of the relative abundance and biting rates of riverine blackflies vectors of onchocerciasis is essential as these entomological indices affect transmission of the disease. Department of plant and environmental sciences, clemson university, clemson, south carolina 296340310, usa. Symptoms include severe itching, bumps under the skin, and blindness. Because the insect that spreads the disease breeds and lives near fastflowing rivers and streams. In children aged 110 years, the prevalence of microfilariae mf was 2.
Pdf the blackfly vectors and transmission of onchocerca volvulus. The pattern and speed of displacement of females of simulium damnosum theobald s. On average, symptoms appear between 9 months and 2 years after the initial infecting bite. In our study, we counted the actual number of attacking and successfully feeding s. A manual for rapid epidemiological mapping of onchocerciasis. Many species and subspecies of simulium blackflies can act as vectors. The results of manual treatments may be cornpiled on. The larvae of onchocerca volvulus, a nematode that is most commonly found in tropical africa, yemen, central america, and south america, are transmitted by flies of the genus simulium that breed near fastflowing rivers. In africa, simulium damnosum theobald complex, a group of cryptic species of black flies, is responsible for transmitting onchocerca volvulus leuckart which causes. Onchocerciasis, also known as river blindness, is a disease caused by infection with the parasitic worm onchocerca volvulus. Black fly are small stocky flies, 2 to 5 mm in length, black or dark brown in colour. The flies bite the host and transmit the larvae, and the larvae then mature into adults within the skin and subcutis, forming nodules that typically are not painful. Female black flies feed on blood and are the scourge of many river banks.
Onchocerciasis is caused by larvae of onchocerca volvulus transmitted through blackflies of the genus simulium, present on river banks. These black flies breed in fastflowing rivers and streams, mostly in remote villages. When a parasitized female blackfly takes a bloodmeal from a human host, the infective onchocerca larvae, pass from the blackfly into the hosts skin and enter the hosts subcutaneous tissue, where they migrate, induce nodule formation, and mature into adult worms over a period of 612 months. When a female simulium blackfly bites an infected person during a blood meal, microfilariae are. River blindness is transmitted by infected simulium black flies living. Blackfly ecology and onchocerca volvulus transmission in three. The blackflies that transmit the parasite bite during the day. Pdf detection of onchocerca volvulus infection in simulium. Individual exposure to simulium bites and intensity of. It is commonly known as river blindness because the black fly. Onchocerciasis, also known as river blindness, is the second leading cause of preventable blindness after trachoma. Seasonal variation in onchocerciasis transmission by. Biting rates and relative abundance of simulium flies.
Females simulium black flies seek blood meals after mating, and thus ingest microfilariae if the meal is taken from an individual infected with onchocerciasis. The pattern and speed of displacement of females of. Development of a novel trap for the collection of black flies of the simulium. These flies breed in fastflowing streams and rivers, hence the name river blindness. Onchocerciasis is transmitted through the bites of simulium blackflies. Onchocerciasis and simulium control in the volta river basin. Onchocerciasis is an infection caused by the nematode onchocerca volvulus.
Simulium venustum are attracted to the carbon dioxide that the host exhales. This information on onchocerciasis vectors seasonal variation, diversity, parity, and biting time are important factors that to be considered for noticeable suggestions in monitoring transmission levels to guide the regional and national onchocerciasis elimination programs in ethiopia. These flies have long segmented antennae of about 11 segments, and all immature stages are aquatic, or at least live in very moist environments. Black flies of the genus simulium are best known for their public health importance as vectors of parasitic nematodes that cause onchocerciasis in many tropical parts of the world tang et al. Robles in guatemala linked blindness with onchocerciasis. The fly was eliminated by the periodical application of ddt emulsion to all infested rivers and streams in the locality. Black flies, onchocerciasis, prevalence, amusement park.
The eradication of simulium neavei, roubaud, from an. An estimated 177 million persons are infected with the parasite onchocerca volvulus, the vast majority of whom live in africa. Characterization of the simulium species of the transmission zone. Infection may result in symptoms varying from dermatological changes to blindness. River blindness or onchocerciasis is a fi larial disease transmitted to man in west africa by black flies of the simulium dam nosum theo. Analyses of data collected routinely by the world health organization onchocerciasis control programme in west africa showed that the transmission of onchocerciasis by simulium squamosum at amouoblo, in togo, was maximal in the dry season. Over 2,200 species of black flies have been formally named, of which 15 are extinct. Thus, blacklock collected several wild simulium damnosum flies and proceeded to infect them by placing the.
Simuliidae across the onchocerciasis control programme area of west africa in 1977 and 1978 volume 75 issue 1 c. Investigations on the transmission potentials of simulium. An onchocerciasis area in south kavirondo, kenya colony, 65 square miles in extent, has been freed from simulium neavei 2. Onchocerciasis is a disease caused by a parasitic filaroid worm named onchocerca volvulus. The simulium control scheme at abuja, northern nigeria. The black fly common name sometimes indicates host specificity, for example the turkey gnat. They are related to the ceratopogonidae, chironomidae, and thaumaleidae. Onchocerciasis river blindness occurs in 34 countries in africa, latin america, and the arabian peninsula figure 1.
Female blackflies need to ingest blood for ovulation, so they feed on humans. Blackflies breed in fastflowing rivers and streams, increasing the risk of infection to people living nearby. Onchocerciasis is a parasitic disease caused by onchocerca volvulus, which is transmitted to humans by black flies genus simulium. The purpose of this paper is to bring together all the available information concerning the control of simulium vectors of onchocerciasis in africa and central and south america some of the larger control schemes are described in detail. This article presents the general epidemiology of the disease and the ways to decrease the number of people being. It is transmitted through repeated bites by blackflies of the genus simulium. Symptoms of onchocerciasis reflect the developmental stage of the parasite and the degree of immune response by the host. River muvur and a large population of flies is infected with onchocerca volvulus. That is the number of new infections that a single human onchocerciasis patient can generate during the lifetime of his infection, when all flies coming to bite on him under natural condition would the transmit the infective l3 into a perfectly naive population. Biting rates and onchocerca infectivity status of black.
Detection of onchocerca volvulus infection in simulium. The simulium damnosum complex in western uganda and its. Onchocerciasis or river blindness is a parasitic disease cause by the filarial worm, onchocerca volvulus. It can cause severe skin and eye disease, including blindness. Pupal stages of simulium were collected and identified from various breeding habitats of twelve locations in northeastern india. Development of a novel trap for the collection of black flies of the simulium ochraceum complex.
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