Lecture 8 - Nematodes: Onchocerciasis Filariasis Flashcards
More than 180 million estimated to have at least one of the human filariases ⇒ Long term suffering & hardship.
Name three important nematode infections.
- Lymphatic filariasis
- Onchocerciasis
- Loiasis
Pathology causes and treatment filariasis:
What is the treament targeted on? Why?
How is pathology caused?
Why is it important to have ‘care in treatment’?
New treatments against the bacterial symbionths (Wolbachia) of microfilaria, because adult worms live for ~17 years and are relatively unresponsive to anti-helminth agents.
Pathology due to dying worms, their bacterial symbionths and secondary bacterial infections.
Care in treatment, because killing all the worms at once may provoke irreversible immune responses.
What is the difference in clinical course between those living in endemic regions and travellers?
Infection is usually asymptomatic, and disease generally occurs only after prolonged exposure and accumulation of worms. - those living in endemic regions.
Travellers may develop severe disease at lower levels of exposure.
Vectors determine filarial distribution:
- Wuchereria bancrofti -
- Brugia malayi -
- Onchocerca volvulus -
- Loa loa -
- Wuchereria bancrofti - GLOBAL (anopheles, culex, aedes)
- Brugia malayi - SE Asia/India
- Onchocerca volvulus - Africa/Americas (blackflies, simulium)
- Loa loa - Africa (tabanid flies)
Adult female Onchocerca volvulus (40 cm) live in humans’ subcutaneous tissue, sometimes coiled within fibrous nodules, where they produce microfilariae (350 μm).
- Where can microfilariae migrate to?
- When do microfilariae develop further? When taken up by blackflies, how long does it take for them to be transmitted into another person?
- How long do microfilariae live?
The microfilariae migrate through the skin and often into the eyes.
Microfilariae only develop further if they are taken up by biting blackflies of the genus Simulium. These flies can transmit infection after a week or more and deposit infective larvae as they bite another person.
Microfilariae live for about 1 year and adults 12 year on average.
Life cycle Onchcerca volvulus:
Start with blackfly (g. Simulium) taking a blood meal and parasites penetrating skin and end with blackfly midgut/thoracic muscle/proboscis stage.
- Blackfly takes a blood meal and third stage larvae penetrate skin wound. In subcutaneous tissue larvae develop into adults and commonly reside in fibrous nodules.
- Female filariae produce microfilariae. The microfilariae are sheathed and are commonly found in skin and lymphatic tissues.
- Blackfly ingests microfilariae and they will migrate from the midgut (and lose sheaths) to thoracic muscles via the hemocoel.
- There the microfilariae develop into first stage larvae and subsequently into third-stage larvae.
- The third stage larvae migrate to blackfly’s proboscis and can infect other humans when blackfly feeds again.
Onchocerciasis (River Blindness) - Onchocerca volvulus.
How is pathology is caused.
Pathology is due to immune reaction to dead and dying microfilariae and Wolbachia symbionths.
How is “leopard skin” caused in ‘late onchocerciasis’?
Intense itching -> healing leads to depigmentation.
What are clinical features of Onchocerciasis (River Blindness)?
- May be asymptomatic
- Skin manifestations
- Subcutaneous nodules
- Eye disease
- General health
River Blindness:
Why do adult worms cause few symptoms? How does pathology arises in onchocerciasis?
Adult worms cause few symptoms, because they evade the host immune response.
Pathology immune reaction to dead and dying microfilariae and Wolbachia symbionts.
A clinical feature in onchocerciasis is “general health”. How is general health affected?
Skin disease may be socially stigmatizing and medication may cause economic loss. Unrelenting itch may result in chronic sleep disturbance and depression. Blind people in village communities have a shortened lifespan.
Skin manifestations are:
- Acute papular onchodermatitis (APOD) - intensely …, papular …, sometimes oedema.
- Chronic papular onchodermatitis (CPOD) - larger, itchy, … papules (Sowda).
- … onchodermatitis - discrete itchy, hyperpigmented papulnodular plaques, often lymphadenopathy.
- Excoriation and … bacterial infection - due to relentless itching. … depigmentation (leopard skin).
- Skin atrophy and depigmentation - loss of … cause wrinkled skin, with inguinal lymphadenopathy -> …. .
- Acute papular onchodermatitis (APOD) - intensely itchy, papular rash, sometimes oedema.
- Chronic papular onchodermatitis (CPOD) - larger, pruritic, hyperpigmented papules (Sowda).
- Lichenified onchodermatitis - discrete pruritic, hyperpigmented papulnodular plaques, often lymphadenopathy.
- Excoriation and secondary bacterial infection - due to relentless itching. Patchy depigmentation (leopard skin).
- Skin atrophy and depigmentation - loss of elasticity cause wrinkled skin, with inguinal lymphadenopathy -> hanging groin.
Eye disease in onchocerciasis (River blindness):
- Describe the difference between early disease (3) and late disease.
- How does ‘snowflake’ opacity appear?
- How is pannus formed?
- Widespread chorioretinitis with pigmentary changes is often accompanied by optic nerve atrophy, what is the result of this?
- Early disease - itching, redness and excess lachrymation.
- Late disease - varying degrees of vision loss and eventually blindness.
- ‘Snowflake’ opacity - due to reactions to death of microfilariae.
- Pannus forms as blood vessels invade the cornea and covering pupil can cause blindness.
- Optic nerve atrophy - affecting central vision - tunnel vision.
How is Onchocerciasis (River Blindness) diagnosed?
- Skin snipping
- Punch biopsy
- Slit lamp (look for microfilariae in anterior chamber of eye)
- Rapid diagnostic tests (LIPS)
What are African programma challenges in Onchocerciasis?
- Civil strife and conflict
- Insufficient health infrastructure, resources
- Political commitment
