Umm Al-Qura University بسم الله الرحمن الرحيم Umm Al-Qura University Health Sciences College at Al-Leith Department of Public Health Lecture (10)

1- Onchocerca volvulus (Onchocerciasis or river blindness) and 2- loaloa (loaiasia)

Objectives 1/ Know of Onchocerca volvulus and Loaloa classification and Geographical distribution. 2/ Study of Onchocerca volvulus and Loaloa External Morphology , Habitat, Life cycle, Mode of Transmission, Pathogenicity. 3/ Show Symptoms of River blindness disease. 4/ Show Laboratory diagnosis of Onchocerca volvulus and Loaloa. 5/ Know Treatment and prevention.

Classification Phylum: Nemathelminthes Class: Nematodea Subclass: Secernentea Order: Spirurida Superfamily: Filarioida Family: Filarridae Genus: Wuchereria Brugia Onchocerca Loa loa Mansonella

1- Onchocerca volvulus

Adults of Onchocerca volvulus Microscopic section showing adults and scar tissue reaction around them forming the nodule Skin nodule cut open to reveal adults coiled together

1- Onchocerca volvulus is a nematode that causes onchocerciasis or "river blindness“. 2- Humans are the only definitive host for O. volvulus. 3- The intermediate host or vector is the black fly (Simulium).

Geographic Distribution  Onchocerca volvulus, occurs mainly in Africa, with additional foci in Latin America and the Middle East. ________________________ ____________ _________________________________________________________  

Life Cycle of Onchocerca volvulus 3. Microfilariae in the skin are ingested by the _____________________ - Simulium damnosum - when a blood meal is taken.

1- The life cycle of O. volvulus begins when a parasitised female black fly of the genus Simulium takes a blood meal. 2-The microfilariae form of the parasite found in the dermis of the host is ingested by the black fly. 3- The microfilariae then penetrates the gut and migrates to thoracic flight muscles of the black fly, entering its first larval phase (L1). 4-After maturing into( L2), the second larval migrates to the proboscis where it can be found in the saliva. Saliva containing stage three(L3).

5- O. volvulus larvae passes into the blood of the host 5-  O. volvulus larvae passes into the blood of the host. they form nodules and then mature into adult worms over a period of 6-12months. 6- After maturation, the smaller adult males migrate from nodules to subcutaneous tissue where they mate with the larger adult females, which then produce between 1,000 and 3,000 microfilariae per day. 7- The normal adult worm lifespan is up to 15 years. The eggs mature internally to form stage 1 microfilariae,

8- These stage 1 microfilariae are taken up by black flies upon a blood meal and then mature in 1-3weeks to stage three larvae, 9- The normal microfilariae lifespan is 1–2 years.

symptoms Symptoms include: 1- severe itching, 2- bumps under the skin, 3-  blindness It is the second most common cause of blindness due to infection, after trachoma

pathology About 17 to 25 million people are infected with river blindness, with approximately 0.8 million having some amount of loss of vision.

Pathology of Onchocerca volvulus ADULTS cause _____________ ______________________________________________________ Nodules are about ½ -1 inch in diameter. Nodules are relatively benign and cause only some disfigurement.

Pathology of Onchocerca volvulus MICROFILARIAE cause 3 severe problems. This is the only filarial worm in which microfilariae are pathogenic! 1. Microfilariae in the skin cause severe ______________________ skin becomes ________________ ________________________   ___________________________ occurs leading to secondary bacterial infections - itching is so severe some people have committed suicide

Pathology of Onchocerca volvulus 2. Microfilariae invade the eye   - ___________________________ _____________________________ occur as microfilariae die in the eye - fibrosis causes clouding of cornea and aqueous and vitreous humors resulting in blindness - fibrosis of the eye is a slow development and most affected persons are _____________________________

Pathology of Onchocerca volvulus 2. Microfilariae invade the eye cont:   In many parts of Africa, the sighted young are responsible for leading the older blind adults.

Diagnosis 1- The most common method of diagnosis is the skin snip. 2- Typically 6 snips are taken from different areas of the body. 3- Polymerase chain reaction (PCR) of the skin can allow for diagnosis if the larvae are not visualized. 4- In patients with nodules in the skin, the nodule can be surgically removed and examined for adult worms.

Treatment Ivermectin, which will need to be given every 6 months for the life span of the adult worms

Prevention and control 1- No vaccine. 2- Protective measures include: # avoidance of black fly habitats. # and the use of personal protection measures against biting insects.

2- loaloa

Caustive Agent : Loa loa Final or definitive host: Human. Intermediate host orVector: Chrysops

chrysops

Pathology of Loa loa Adults cause localized inflammatory reactions in the skin called Calabar swellings. Eye swells when worms migrate through. Loa loa is rather benign compared to other filarial worms.  

Life cycle of loaloa

Thanks Radia 32