1. Loa loa: A neglected NTD
Thomas B. Nutman, M.D.
Head, Helminth Immunology Section and
Head, Clinical Parasitology Section
Laboratory of Parasitic Diseases
National Institute of Allergy and Infectious
Diseases

2. Loiasis
• Ogranism-Loa loa
• Vector - Chrysops spp. (deerfly)
• Microfilariae: Blood-borne
• Adult worms: subcutaneous
• Prevalence - ?3-13 million
• Geographic Distribution - West and Central
Africa
• Host range - Human

3. Geographic distribution of loiasis

4. Lifecycle of Loa loa
(EGG)
L1
ADULT
L4 L2
L3

5. Loiasis - Clinical Manifestations
• Asymptomatic
• Non-specific
– urticaria, pruritus, myalgias
• Calabar swellings
• Eyeworm
• Complications
– Endomyocardial fibrosis, renal disease,
encephalopathy, entrapment neuropathy

6. Loiasis – Calabar Swellings
•Episodic angioedema
•Most common on
extremities
•Duration -1-4 days

8. Parasite
Host
Hyper- Responsive Responsive Hypo-responsive
responsive (appropriate) (inappropriate) (tolerant/suppressed)
Unusual Immunity Pathology Infected
Pathology

9. Loiasis: Diagnosis
• Definintive diagnosis
– Detection of microfilariae in daytime blood
– Identification of adult worm in the
subconjunctiva or subcutaneous tissue
– PCR using Loa loa repeat sequence
• Presumptive diagnosis
– Compatible clinical picture + positive
antifilarial antibodies
• Problematic due to geographical, serologic and
clinical overlap with other filarial infections

11. Loiasis: extraction of adult worm

12. Loiasis: treatment
• Diethylcarbamazine (DEC)
– treatment of choice (8-10 mg/kg/d x 21
days)
– mechanism of action unknown
• immune system dependent
• macro- and microfilaricidal
– associated with severe side effects in
patients with high levels of circulating
microfilariae

13. Loiasis: adjunct therapy
• Corticosteroids
– decrease rate of microfilarial clearance
– reduce severity of post-treatment reactions
– DO NOT prevent severe CNS complications of
treatment in patients with high microfilarial
load
• Apheresis
– transient reduction of microfilarial load
– ?decreased incidence of severe side effects

16. Loiasis response to therapy
Median years of follow-up: 4.5 years (range 2-15 years)
Cure rates with DEC
•1 course 38% (12/32)
• 2 courses 54% (17/32)
• ≥ 3 courses 90% (23/32)
The remaining 3 patients were cured following a 3 week
course of albendazole.
Klion A, Ottesen E, Nutman T. J Infect Dis. 1994 Mar;169(3):604-10.

17. Loiasis and ivermectin
• Between 1989 and 1998, 76 million doses of
ivermectin were distributed with 84 SAEs
reported by passive surveillance (1 case/million)
– 65/84 (75%) from Southern Cameroon
– 37/65 (60%) were neurologic, 25% of which had high
levels of Loa microfilaremia
– the encephalopathy was temporally related to
Mectizan™ (<5 d post-rx) and occurred in previously
healthy individuals

18. Acknowledgements
•Doran Fink • Past and present LPD
•Amy Klion Clinical Staff
•Peter Burbelo – LPD Clinical Fellows
•Susan Leitman – Kate Spates
•Jesica Christensen – Nicole Holland
•Dan Fedorko – Amara Pabon
•Gary Fahle – Melissa Law
– Cheryl Talar-Williams