Parasitology on Onchoceca volvulus group 6.pptx

Parasitology and pest control

1. ONCHOCERCA VOLVULUS Trymore Mhlanga Tendai Muduma Tanatswa Mugauri Brendon Msipa Carol Mugumbo Simbarashe Mugezi

2. Introduction Onchocerca volvulus is a nematode which causes onchocerciasis . It is propagated by a black fly of the genus simulium . They are found around plantations following rivers and river basins. The pupae are attached to submerged objects in running water from which they extract oxygen through head filaments. Moving and highly oxygenated water in streams provide the essential ecological environment for them.

3. EPIDEMIOLOGY Onchocerciasis is an infection caused by the parasitic worm onchocerca volvulus . It is a filarial disease found chiefly in tropical Africa, Yemen, South and Central America It is spread by the bite of an infected female similium called the black fly. Onchocerciasis is also called river blindness because the fly that transmits the infection breeds in rapidly flowing streams and the infection can cause blindness

4. Onchocerca volvulus It can affect both children and adults. Persons with infection will show signs of the disease after 4 to 18 months of the infective silium bite Most at risk are those who work or live for long periods in close contact with the vectors of the disease in the breeding places either in shallow flowing streams or in neighbouring fields

5. PATHOLOGY There are skin fibrous nodules ( onchocerca tumours) enclosing female worms. The nodules are common in the neck, iliac chest and coccyx Dermatitis is present and in advanced cases skin becomes thickened and wrinkled showing lizard or leopard skin appearance. This is caused by lodging of filariae in the subcutaneous layer Elephantiasis of the external genitalia may occur Skin pigmentation occurs mostly on legs Corneal opacity and optic atrophy may finally cause blindness or lead to visual impairment Other persons may manifest skin rash.

6. LIFE CYCLE

7. Continuation…. A silium female takes a bloody meal from an infected host and ingests microfilaria Microfilaria enter the gut and thoracic flight muscle of the black fly ,progressing in to the 1 st larval stage L1 The larva mature in to the 2 nd larval stage and move to the proboscis and in to the saliva in its 3 rd stage which is the infective stage. Maturation takes about 7 days The black fly takes another bloody meal passing the larvae into the next human host blood The larvae migrate to the subcutaneous tissue and undergo 2 more molts . They form nodules as they mature into adult worms over 6 to 12 months

8. Continuation …. Females initiate the formulation of the nodules and the males join later. After maturing the adult male worms mate with female worms in the subcutaneous tissue to produce between 700 to 1500 microfilaria per day Microfilaria migrate to the skin during the day and the black fly only feed in the day so the parasite is in a prime position for the female fly to ingest it. The black fly then ingest these microfilaria to restart the cycle

9. MORPHOLOGY It is a white adult worm that lies coiled within the capsules in the fibrous tissue The female measures 30cm to 50cm Males are similar to wuchereria bancroft and are shorter than females measuring up to 5cm and 0,02mm wide Males have a spiral shaped tail and the ventral side near the tail have 2 pairs of small papillae each containing 2 capillary spiculars measuring about 0.6mm to 0.2mm The anterior end is hemispheric with a slight constriction immediately behind and has small papillae Lips in buccal cavity are both lacking

10. DIAGNOSIS Superficial biopsy (skin snap) is taken from the skin . The specimen is allowed to stand for 30 min in saline before it is examined microscopically for microfilariae In patients with nodules in the skin, the nodules can be surgically removed and examined for adult worms Infections in eyes can be diagnosed with slit –lamp examination of the anterior part of the eye where the larvae or the lessions they cause are visible Antibody tests have been developed to test visitors for infection

11. Clinical manifestation Clinical manifestations Cause visual impairments like, corneal opacity, glaucoma and finally blindness Lymphadenitis of legs and external genitalia

12. Clinical manifestation Cont.. skin nodules (common in the head and neck) inflammation- skin may be hot, edematous and very itchy Atrophy of the skin resulting in loss of elasticity Skin depigmentation- leopard skin

13. PREVENTION AND CONTROL Avoid bites from black flies by using protective clothing or clothing Use of insecticide such as abate or chlorphonic for treatment of streams in the endemic areas during the similium breeding seasons . Helicopters or light aircrafts are used for accurate spraying of insecticides over long stretches of affected rivers Chemotherapy. W.H.O and other U.N agencies have recently launched a 20 year programme for the elimination of onchocerciasis in the Volta river basin in west Africa using the spray programme Mass treatment Location of villages away from similium breeding places

14. Prevention contro l Fly screening of windows and doors Use of ivermectin to treat infected cases. People can be treated with ivermectin six months apart repeated every 3 years. This can stop skin itchiness and progression towards blindness is halted. The drug prevents adult worm from producing additional offspring . The drug therefore reduces morbidity and transmission Elimination of crabs on which immature stage of larvae develop Report to the local health centre for investigation Provide facilities for diagnosis and treatment

15. REFERENCES Duke, B.O.L (1990), Onchocerciasis : A Review , 1 st Edition, Springer, New York, USA. Horton, J, (2003), Onchocerciasis : The River Blindness , Cambridge University Press, UK. M cKerrow , J.H and Caffrey , C.R, (2017), Onchocerca Volvulus: Biology and control , Springer, Belin, Germany. Rwaiyuru,I and Ndyomugyenyi , R, (2020), Advances in the Study of Onchocerciasis , Academic Press, London, UK. Mabey , D, (2013), Onchocerciasis and its control, 2 nd Edition, World Health Organization , Geneva, Switzerland. Aluko , A.J, (2015), Onchecerciasis : A review of the Literature, Journal of Parasitology Research, Cairo, Egypt.