Loa loa

Question 1

What is the organism that causes loiasis?

Answer 1

Loa loa

Question 2

What is the vector of loiasis?

Answer 2

‘Deer’ fly of the genus Chrysops

Question 3

Describe the lifecycle of Loa loa

Answer 3

1. During a blood meal, an infected fly (genus Chrysops, day-biting flies) introduces third-stage filarial larvae onto the skin of the human host, where they penetrate into the bite wound
2. The larvae develop into adults that commonly reside in subcutaneous tissue
3. The female worms measure 7cmx0.5 mm, while the males measure 34 mmx0.4 mm
4. Adults produce microfilariae measuring 300x8 μm, which are sheathed and have diurnal periodicity. Microfilariae have been recovered from spinal fluids, urine, and sputum. During the day they are found in peripheral blood, but during the noncirculation phase, they are found in the lungs
5. The fly ingests microfilariae during a blood meal
6. After ingestion, the microfilariae lose their sheaths and migrate from the fly’s midgut through the hemocoel to the thoracic muscles of the arthropod
7. There the microfilariae develop into first-stage larvae number
8. and subsequently into third-stage infective larvae
9. The third-stage infective larvae migrate to the fly’s and can infect another human when the fly takes a blood meal

Question 4

How long do adult L. loa worms live? The Microfilaria

Answer 4

• Adult = Up to 15 years
• Microfilaria = up to 2 years

Question 5

What are the symptoms of loiasis? What is the main cause of the symptoms?

Answer 5

• Mostly asymptomatic
• Urticaria
• Pruritis
• Arthralgia
• Malaise
• Pain and inflammation in the eyes following subconjunctival migration
• Calabar swelling following trauma to an adult worm resulting in local inflammation

Symptoms are mainly attributable to the adult worm

Question 6

How can loiasis be diagnosed?

Answer 6

• History and examination if eye worms are present
• Peripheral blood microfilaremia that peaks between 1000 and 1500 hrs
• Hyper-eosinophilia

Question 7

What is the treatment for loiasis with high microfilaremia? Considerations for treatment?

Answer 7

In patients with high L. loa microfilaremia
* Albendazole 200mg bd for 3 weeks to reduce microfilarial load
* Followed by DEC most commonly (or ivermectin)
* Microfilarial loads need to be decreased <8000 Mf/mL otherwise there is risk of encephalopathy with either DEC or ivermectin

Question 8

What is the distribution of L. loa

Answer 8

West and Central Africa

Question 9

What time of day does the Chrysops (Deer Fly) bite

Answer 9

Day biting

*Important as peripheral blood microfilaremia peaks between 1000 and 1500 hrs is important for diagnosis

Question 10

True or false: Loa loa is dependent on Wolbachia bacteria endosymbiont

Answer 10

False - Loa loa does not depend on Wolbachia

Therefore doxycycline is not useful in treating Loiasis

Question 11

What is the preferred treatment for loiasis in patients with low microfilarial loads?

Answer 11

DEC (2mg/kg) orally TID for 7-10 days

DEC is macro AND microfilaricidal

Question 12

What countries have high rates of loiasis infection?

Answer 12

Central Africa
1. Cameroon
2. Equatorial Guinea
3. Gabon
4. Congo
5. DRC
6. Angola
7. Central African Republic
8. South Sudan
9. Chad

West Africa
1. Nigeria