Onchocerca volvulus

1. Onchocercavolvulus Ross Boreen and Ellyn Krieg

2. Taxonomy • Onchocercavolvulusis a filarial worm • The diseases it causes is onchocerciasis • Depending on where it infects the host it can be further classified as river blindness or filariasis • It is one of the three nematode worms that causes subcutaneous filariasis • Loa loa • Mansonellastreptocerca • Onchocercavolvulus

3. Geographical Range and Hosts • Found in 36 countries endemically with 30 of them being in sub-Saharan Africa commonly found in Central America as well • Roughly 80 million people are infected • In hyperendemic areas more than 90% of people can have the microfilariae

4. Hosts • Definitive Host: Humans • Intermediate Host: Female Simulium flies (black flies)

5. Morphology • Adults: • Found in pairs or groups • Slender and blunt at both ends • No lips or buccal capsule • Two circles of four papillae which surround the mouth • Males are 19 cm to 42 cm long • Females are 33.5 cm to 50 cm long • Male posterior end is curled ventrally and has four pairs of adanal and 6-8 pairs of postanal papillae • Microfilariae: • Unsheathed • Sharply pointed and curved tails

6. Life Cycle

7. Life Cycle Continued • Simulium fly introduces L3 larvae into the skin of a human as it takes a blood meal • In subcutaneous tissues the larvae develop into adults both male and female commonly forming nodules called onchocercomas • The adults can live in these nodules for 14-16 years. While here the female will produce up to 1000 microfilariae/day for up to 9 years. • Microfilariae travel throughout the skin and lymphatics of connective tissue, but can also be found in the peripheral blood in heavy infections. • Black fly ingests the microfilariae during a blood meal

8. Life Cycle Continued • Microfilariae migrate from the midgut through the hemocoel to the thoracic muscles where they develop into L1 larvae. They then molt twice into L3 larvae • The L3 larvae migrates to the proboscis of the fly. • The L3 is transmitted to another human when the fly takes another blood meal. • The time the microfilariae takes to develop into an L3 larvae in the fly is about 10 days.

9. Pathogenesis of Adults • Not very pathogenic, often no symptoms • Can cause subcutaneous nodules called onchocercomas over bony prominences • In African strains tend to be on lower body such as pelvic area, and some along the spine, chest, and knees • In Central America they are on the upper body with most being on the neck and head • Nodules are pretty benign just cause disfigurement with no pain • They are composed of collagen fibers surrounding the adult worms • Occasionally the nodule can degenerate to form an abscess or the worms can become calcified

10. Pathogenesis of Microfilariae • Live ones cause little inflammation • Can cause a dermatitis or eye complications • Dermititis (Filariasis) • When they die they start to degenerate which causes severe dermatitis • Dermatitis thought to be caused by release of a type of bacteria called Wolbachia, which can be treated with doxycycline to help reduce inflammation • First sign is intense itching, which can lead to secondary bacterial infections and death of patches of skin • After the itching the, skin thickens, becomes discolored, and cracks, a process known as lichenification • Characterized by loss of elasticity making the patient look like they are aging prematurely • Lymph glands that serve the area of infected skin can become inflamed as well

11. Riverblindness • Eye lesions take many years to develop so most often not found in anyone under 40 in Africa however in Central America can be found in younger adults • Microfilariae can invade many parts of the eye but do not cause many problems until they die • Once dead a similar inflammation reaction to the skin reaction occurs causing lesions • Most common cause of blindness is sclerosingkeratitis (a type of inflammation of the cornea that leads to hardening of the cornea) • Inflammation in the eye is the result of de-granulating eosinophils disrupting the arrangement of the cornea • Also causing inflammation is activation of toll-like receptor 4 by Wolbachia antigens which produces many proinflammatory cytokines

12. Diagnosis • Most common method is a skin snip • Small piece of skin is pulled up and cut off with razor or scissors • Placed in saline on a slide and examined for emerging microfilariae • Nodules can be aspirated but only adults are found this way • DEC (diethylcarbamazine) as a confirmation of diagnosis

13. Treatment • Removal of nodules can help with lowering rate of eye damage and rate of infection • Ivermectin now replacing DEC and suramin due to its low rate of serious side effects • A microfilaricide- a single dose eliminates the microfilariae however it does not kill the adults but stops the female from releasing microfilariae for a year • Repeated dosing of Ivermectin can slowly kill the female

14. Prevention • Vector control • DDT • Avoid fast flowing rivers since vector breeding ground • Larvicide in fast flowing rivers • Combine with drug campaigns • Onchocerciasis Control Programme from ended in 2002 but prevented 125,000-200,000 people from going blind and protected 30 million people from ocular and skin lesions

15. Review • What are the hosts for Onchocercavolvulus? • What are the two types of disease that the microfilariae can cause? • Where is Onchocercavolvulusfound? • What is the most common way to diagnose it? • What is the name of the drug patch that can be used to confirm infection with Onchocercavolvulus?

16. References • http://www.dpd.cdc.gov/dpdx/html/frames/a-f/filariasis/body_Filariasis_o_volvulus.htm#Life%20Cycle • http://www.science.smith.edu/departments/Biology/SWILLIAM/fgn/pnb/oncvol.html • http://www.who.int/apoc/onchocerciasis/lifecycle/en/index.html • http://plpnemweb.ucdavis.edu/nemaplex/taxadata/Ovolvulus.HTM • Foundations of Parasitology Eight Edition by Roberts and Janovy