27 Onchocerciasis - “River Blindness”

Paul Pottinger 19/09/18

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Years of intensely itchy skin, loss of pigment where scratched, gradual onset of blindness

  • Blindness
  • Dermatitis
  • Seizure Disorder

27.1 Epidemiology

Not exclusively an african disease, also some taken across to the new world

Greatest burden seen in SSA. Most in Nigeria

Around ~5% are blind

27.2 Life Cycle

Black fly (the buffalo fly) - matures in fast running water, underwater

The patient is bitten, a black fly punches out a bit of skin, so a pool of blood forms.

MF head into subcutaneous tissues. They don’t need to go to lymphatics, they form subcut nodules. New MF stay in SC tissues.

Most of the disease in oncho is due to the MF (whereas in lymphatic filiarisis it’s the adults)

These nodules can be palpable.

Anthoponosis - no big animal vector

Worms do have endosymbiotic wolbachia like seen in LF

This is a low-efficienct vector, its rare for tourists out in short distance to get.

27.3 Clinical Features

West African Savanna: Anterior Ocular Disease Predominates

African Forests: Skin Disease Predominates

Why are there different patterns? Maybethe wolbachia

27.3.1 Presentation

27.3.2 Skin

  • Texture/Colour changes
  • Toughening of skin (lichenification, “lizard skin”)
  • Hyper/hypo pigmentation at areas of scrathing (“leopard skin”)
  • Sagging skin
  • Bacterial superinfection

27.3.3 Nodules

  • Raised, round, firm. 2-3cm
  • Not mobile. They are fixed.
  • For each one you could see. ~5 lie deeper
  • Each holds at least one adult worm

Nodules are disfiguring but not the itchiest. Not red or inflamed.

Seen more in head in africa, seen more on trunk in americas

27.3.4 Lymphatics

“Equitorial Arm” - Transient Lymphatic Blockage. Not the same as elephantiasis. Lasts for a couple of days and then resolves.

Can see lymphadenopathy, this can become dependent lymphadenopathy.

27.3.5 Eye

Caused by MF migration and inflammation

Any part of the eye can be affected:

  • Anterior Disease (keratitis, uveitis)
  • Posterior Disease (chorioretinitis, optic atrophy)

27.3.6 Nodding Syndrome

Generally only seen in Uganda, in children.

Constellation of: narcolepsy, behavioural symptoms, rhythmic nodding symptoms of head and neck

Stongest current hypothesis is that it is an immune reaction to onchocerca

Abnormal expression of leiomodin

27.4 Diagnosis

27.4.1 Skin Snip/Punch Biopsy

Take a small piece of skin, to the dermis. Put it in saline, see what worms wiggle out. Try staining the worms in saline

6 punch biopsy, over scapulae and hips. Relatively painless

27.4.2 Nodule Excision

See the adults in it

27.4.3 Eye Disease

Opthalmology exam with slit lamp

You can sometime even see the MF!

27.4.4 Bloods

Eosinophilia, really should have a v high level

27.4.5 Microscopy

No sheath, no nuclei in tail (onchocerca volvulus)

27.4.6 DEC Patch test

These worms are exquisetly sensitive to DEC. So a skin solution causes extreme dermatitis.

Mazotti Test: Give tiny dose of DEC (25mg orally, or a small patch). This causes itching in patients who have oncho. It kills microfilaria in skin, causing itching. Only done in patients when skin snips are negative. Sometimes if you repeat the punch biopsy where the itching was, you now find the MF

Mazotti Reaction: If you give the full dose treatment for LF, you now cause extreme pruritis, angioedemea, anaphylaxis, patient death!

27.5 Treatment

You don’t want to give them DEC

27.5.1 Ivermectin

150mg O QID up to 6 months

Inhibits maternal MF release, making you feel better, inhibiting transmission

But does not reliably kill adults. And they’re lifespan can be up to 14 years

And really bad for Loa Loa infection. As it may aid Loa penetration into CNS, causing encephalitis. So you need to treat for loa in advance.

27.5.2 Doxycycline

To kill off the adult worms by targetting the wolbachia

27.6 Prevention

Kill off the vectors with larvicides and use larva eating fist

There are big public health approaches, with APOC

27.7 Summary

  • Onchocerca volvulus infection via simulium fly
  • Savanna areas: Eye pathology predominates

  • Forest areas: Skin pathology predominates

  • Diagnosis: Skin snips, slit lamp
  • Rx: Goal: reduce symptoms, prevent blindness
  • Ivermectin to reduce mf release
  • Doxycycline to kill wolbachia

  • Watch out for Loa Loa Co-Infection

  • Prevention: Periodic Mass Ivermectin Dosing -Future: Better drugs? Sustained commitment?