25 Loa Loa

Jo Jarvis 19/09/18

25.1 Life Cycle

Loa Loa is a nematode, a round worm

Bitten by a chrysops fly, injecting a larvae, these mature into an adults around 4-7 cm long

These worms roam around the subcutaneous tissues

In loa loa the MF are in the blood

25.2 Vector

Lives in heavily forested areas in west and central africa

Chrysops fly

Require years of exposure before infection. So rare among travellers

25.3 Epidemiology

RAP-LOA survey

Worst in GAbon, Congo, Equatorial Guinea, Some in DRC and CAR and Cameroon

25.4 Pathophysiology

Adults migrate across sub cut tissue

It’s the adults that cause the pathology through migration.

25.5 Clinical PRrestntation

  • Asymptomatic
  • Calabar Swellings
  • Eye worm
  • Other

25.5.1 Calabar Swelling

Not known why they happen

Named after a town in nigeria

25.5.2 Eye worm

They cross across the surface of the eye. On the conjunctiva

Doesn’t really itch or sore

25.5.3 Systemic Symptoms

  • Chronic Fatigue - seems to get better when worm is removed

  • Eosinophilia, worse in travellers probable

  • Hypereosinophilic cardiomyopathy,
  • nephropathy

  • inflammatory encephalitis (especially post-DEC)

25.6 Diagnosis

Loa Loa is the only for eye worms.

But other things can cause flitting subcut swellings and eosinophilia

25.6.1 Lab

  • Eosinophilia
  • Filarial Serology (but remember cross reactivity over filaria)
  • Blood Film (day bloods)

25.6.2 Treatment

  • Not usually needed
  • Can surgically treat but not recommended

Drugs with DEC

Loa loa doesn’t have the commensal bacteria, so can’t use doxycycline

DEC kills microfilaria quickly. You can get a marked eosinophila reaction. Including an encephalopathy. If the microfilarial load is high, the risk is high.

If MF count >2500 we need to reduce the load first, by using ivermectin? but it also can cause encephalopathy. Albendazole is safer but takes longer.

25.6.3 Public Health - Onchocerciasis Control

The problem here is the overlap with onchocerciasis. You treat that with ivermectin. But give that to loa loa you might cause encephalitis!

So in areas with a lot of loa loa, the onchocerciasis control cannot be done!

So you can use the RAP-LOA map to work out where is safe for onchocerciasis control.

25.6.4 DEC in onchocerciasis

So treating loa loa may go badly wrong if they’ve also got onchocerciasis.

You need to do skin snips for onchocerciasis first.

If they have oncho, treat with doxy first. Maybe 6 weeks or so.