Onchocerciasis

Onchocerciasis is a river blindness disease caused by the filarial nematode parasite Onchocerca volvulus.

1. ONCHOCERCIASIS, NIG ER IAN PERSPECTIVE B Y UWAMOSE , Martin Nelson Osaigbokan

2. INTRODUCTION Onchocerciasis a River Blindness disease is a chronic parasitic multi systemic disease caused by the filarial nematode Onchocerca volvulus . The parasite causes blindness and severe skin diseases in tropical regions of the world. Approximately 18–44 million individuals in the world have Onchocerciasis infection. It is the second-leading infectious cause of preventable blindness in the world after Trachoma (WHO 2012). Man is the only definitive host of this parasite and acquire infection through the bite of black fly (genus Simulium ). The damage caused by this disease is irreversible. When someone is blinded by the parasite there is no cure; you can only kill the parasites.

3. PREVALENCE IN NIG ER IA Nigeria is the most endemic country in the world for Onchocerciasis . First reported in northern Nigeria in 1908 ( Budden 1956). Endemic areas extend from the North, Southwest & Southeastern part of the country with highest prevalence in Zamfara , Kwara - NW Nigeria and Enugu, Imo, Ebonyi - SE Nigeria (Meredith 2012) The provisional estimates had suggested that 7–10 million Nigerians are infected with Onchocerca volvulus , approximately 40 million are at risk of the disease and 120,000 cases of onchocerciasis -related blindness (WHO 2010). The disease is lower in individuals between the age of 0–10 years but increases with a peak in individuals between the age of 20-30 years ( Uttah 2010).

4. States boundaries Lakes Absence Presence Fig. 1: Map showing the presences of Onchocerciasis in Nigeria Source: WHO 2010

5. VECTOR AND TRANSMISSION The only known vectors of O. volvulus are the female black flies of the genus Simulium . The fly bites during daylight hours. Eggs require fast-running rivers which have well-oxygenated water for breeding grounds. This is important because larvae of O. volvulus have an obligatory aquatic stage during which they require a high oxygen tension. Adults emerge after 8-12 days following egg production. The adult fly has the ability to travel hundreds of kilometres in flight on wind currents. Their life span is about 4 weeks.

6. Fig. 2: Female black fly of the genus Simulium Source: WHO 2010.

7. MORPHOLOGY OF THE PARASITE Adult worms are white, opalescent and transparent. They are slender and blunt at both ends. They are usually found knotted together in pairs or groups in subcutaneous tissues. Males measures 1.9-4.2cm in length and has a coiled tail. The females are much longer, measuring 33.5-50cm in length. Adult worms live long; the female has an average life span of 8 years.

8. Fig. 3: Onchocerca volvulus adult worms Source: Google images.

9. ETIOLOGY: study of the cause of diseases Microfilaria invade the midgut of the fly, advance to the thoracic muscles where they undergo differentiation into L1 larva within 28 hours after the blood meal. They moth twice producing L2 and L3 larva (infective larva) within 06 hours and 7 days respectively. Infective L3 larva migrates to the proboscis for future deposition into human skin during the next blood meal. When the Fly bites another person, Infective L3 larvae are transmitted to human skin.

10. The larvae move under the skin and form nodules where they develop into adult worms in 12 to 18 months. Adult worms pair and mate in the human host. Female Onchocerca gives birth daily to thousands of microscopic larvae (microfilaria) Microfilaria released from the nodules traverse the skin and connective tissue easily. The most common migration sites are subepidermal lymphatics and the anterior chamber of the eye. ETIOLOGY (CONT.)

11. LIFE CYCLE OVERVIEW The black flies breed in fast flowing water and streams. When a Black fly bites an infected person, microfilariae are transferred from the person to the fly. Between 1-3 weeks the microfilariae develop in the fly and become infective larvae. These are passed to the human host and the larvae migrate to subcutaneous tissue, form nodules and slowly mature into adult worms Onchocerciasis is transmitted person to person through the bites of Simulium black fly vectors.

12. Fig. 4: Life cycle of Onchocercia volvulus Source: Google images.

13. Fig. 5: Life cycle of Onchocercia volvulus Source: CDC images.

14. PATHOGENESIS The adult worms and the microfilariae contribute to the pathogenesis of Onchocerciasis . Adult worms isolated in nodules are not directly harmful to the patient, their progeny (Microfilaria) are responsible for the damage related to Onchocerciasis . In some infected persons, 100,000 or more microfilariae die each day. Live microfilariae found in the eye do little, but when they die is the problem. Most microfilariae die as immature worms in the host. Inflammatory and immune reaction to dead or dying microfilariae are responsible for the clinical manifestation. This causes the most important reason of blindness, which is sclerosing (scarring) keratitis , a hardening inflammation of the cornea.

15. SIGNS AND SYMPTOMS The symptoms include: Preventable blindness Skin rashes Lesions Itching Skin depigmentation

16. Fig. 4: Depigmentation over the skin in later onchocerciasis (Leopard skin). Source: Google images.

17. Fig. 5: Eye lesions in Onchocerciasis Source: Google images.

18. Fig. 6: Preventive blindness in Onchocerciasis Source: Google images.

19. DIAGNOSIS The best method for diagnosis is identification of microfilariae in bloodless skin snips. Buttocks and legs are often most heavily infected and are most likely to yield microfilariae. A small piece of skin is raise with a needle and clipped with a razor or scissors.

20. DIAGNOSIS CONT. In heavily infected individuals, microfilariae can even be found in the blood, sputum and urine. Fig. 7: Living microfilariae of Onchocerca volvulus on urine sample Source: Google images Fig. 8: Living microfilariae of Onchocerca volvulus in blood sample Source: Google images

21. TREATMENT The treatment is with a single of Ivermectin ( 150 microglkg ). It kills the microfilaria rapidly, Reduces production of microfilaria from adult worm for several month. After treatment, microfilaria disappears from the skin within 1 week and from eye within 3 months. NOTE: There is no cure; once someone is blind by the parasite, you can only kill the parasites 21

22. PREVENTION AND CONTROL Primary means of preventing Onchocerciasis in Nigeria include: Vector control – applications of environmentally-safe insecticides to the black fly's breeding areas (fast-flowing rivers) during the rainy season. Mass treatment with Ivermectin . 22

23. CONCLUSION Onchocerciasis is one of the neglected tropical diseases of public health concern in Nigeria. It is common in rural area where black flies have favourable environment to habit and reproduce as the outbreak and spread of this disease rely on the activities and survival of black fly. The high prevalence of microfilariae in Nigeria underscore the need for renewed awareness campaign to bring the attention of individuals in endemic areas to the importance of personal protective measures against the infective bites of the black fly vector. This is also a wake-up call to health authorities to embark on massive community treatment with Ivermectin . 23

24. 24 Thanks For Your Time