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Loa loa: A neglected NTD
Thomas B. Nutman, M.D.Head, Helminth Immunology Section andHead, Clinical Parasitology SectionLaboratory of Parasitic DiseasesNational Institute of Allergy and Infectious Diseases
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
Geographic distribution of loiasis
Lifecycle of Loa loa
Loiasis - Clinical Manifestations
• Asymptomatic• Non-specific
– urticaria, pruritus, myalgias
• Calabar swellings• Eyeworm• Complications
– Endomyocardial fibrosis, renal disease, encephalopathy, entrapment neuropathy
•Episodic angioedema
•Most common on extremities
•Duration -1-4 days
Loiasis – Calabar Swellings
Parasite
Host
UnusualPathology
Immunity Pathology Infected
Hyper-responsive
Responsive(appropriate)
Responsive(inappropriate)
Hypo-responsive(tolerant/suppressed)
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
Loiasis: extraction of adult worm
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
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
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.
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
Acknowledgements
•Doran Fink•Amy Klion•Peter Burbelo•Susan Leitman•Jesica Christensen•Dan Fedorko•Gary Fahle
• Past and present LPD Clinical Staff– LPD Clinical Fellows– Kate Spates– Nicole Holland– Amara Pabon– Melissa Law– Cheryl Talar-Williams