A discussion of onchocerciasis.

1. HX
●3 wk hx/o progressively decreased visual
acuity OS
●Intense puritius X 2 months
●Native Kenya from RURAL region near
running water
●In Croatia X 9 mo’s

2. Exam/Laboratory
●Eczematoid dermatitis and
hypopigmentation over legs
●Sclerosing keratitis of inferior temporal
quadrant cornea OS
●Visual Acuity 20/20 OD & 20/200 OS
●90% Eosinophilia on peripheral smear

3. Onchocerciasis
Frank Meissner, LtCol, USAF, MC, FS
Emergency Medicine

4. The fact that illness is associated
with the poor-who are, from the
perspective of the privileged,
aliens in one's midst-reinforces
the association of illness with the
foreign: with an exotic, often
primitive place.
Susan Sontag

5. Biology
●Onchocerca volvulus - Causative Agent
●TISSUE dwelling parasite- filarial
nematode
●Family Onchocercidae

6. Epidemiology
●Equatorial Africa
●Elevated regions of Mexico and
Guatemala
●Smaller foci in Saudi Arabia, Yemen,
Brazil, Ecuador, and Venezuela

7. Pathology
●Adult worms reside in subcutaneous
tissues
●Often enclosed in fibrous nodules
●Microfilariae, which in this species lack
an enveloping sheath
●Released from female adults
●Localize in skin and subcutaneous
tissues

8. Clinical Features I
●Skin is frequently involved
●Pruritus most common clinical
manifestation
●Wrinkling and skin atrophy

9. Clinical Features II
●Hypopigmentation or hyperpigmentation
●Papulovesicular lesions & localized
areas of eczematoid dermatitis
●Firm, nontender subcutaneous nodules
(over boney prominences)

10. Clinical Findings III
●Blindness most feared complication
●1.5K per 100K (endemic region) vs .25K
per 100K (base risk)
●Some areas 10% of adult population
blinded
●Conjunctivitis with photophobia
●Common and earliest finding

11. Clinical Findings IV
●Punctate keratitis (10-15%)
(accumulation of inflammatory cells
around dying microfilariae) usually no
sequlae
●Sclerosing keratitis (5%) and
chorioretinal lesions (5%) cause
blindness
●Anterior uveitis, iridocyclitis (5%) and

12. Vector
●Simulium species (blackflies)
●Simulium damnosum (major African
vector)
●No reservior host
●Estimated 30 million infected in Africa

13. Laboratory Diagnosis I
●Small piece of superficial skin obtained
by excision or punch biopsy weighed
●Incubated for several hours in saline or
tissue culture media
●Microfilariae that exit the skin are then
counted in the fluid
●Count of more than 100 microfilariae
per milligram of skin= heavy infection

14. Laboratory Diagnosis II
●50 mg provocative dose of
diethylcarbamazine
●Subsequent onset of symptoms, which
include pruritus, rash, fever, and
conjunctivitis= Mazzotti reaction
●Eosinophilia is often prominent during
onchocerciasis

15. Treatment I
●Diethylcarbamazine (DEC) 2 wks of 3 to
4 mg/(kg*day) in 2 divided doses
●25 mg test dose prior to giving
theraputic dose
●Pretreatment of patient with
corticosteroids and ASA reduce somatic
side-effects
●Microfilaricidal agent ONLY
●Leads to symptomatic improvement and

16. Treatment II
●Ivermectin, given orally in a single dose
of 150 mg/kg
●This dose is repeated every six to 12
months
●Nodulectomy for large nodules (remove
the adult worms)

17. Life Cycle I
●INNOCULATION by the bite of female
blackfly
●Infective larvae develope into adult
worms
●Coil into spherical bundles with 2-3
females + one to two males
●Gravid females release microfiliariae

18. Life Cycle II
●Microfiliariae migrate to host tissues
(esp dermis)
●Transmission intitiated by bite of fly onto
infected individual
●Microfiliariae migrate to BlackFly
thoracic muscles and become larvae
(6-8 d’s)
●Larvae migrate to head of fly and cycle

19. Conclusions
●Geographic Medicine NOT Tropical
Medicine
●Modern aircraft and mobile patients
make these diagnosises to consider
●Knowledge of parasitic infections
important

20. Meissner 6 W’s- ID Hx/o
●WHERE & WHEN? (travel history)
●You did WHAT WITH WHO, WHERE ?!!!!!!!!
(sexual history)
●WACKY WAYS to WASTE time?
(avocational/occupational history)
●WEIRD and non-WEIRD WILDLIFE?
(Zoonoses)
●Wolfing WHAT? (food and ingestion history)
●WEAK-knead WIMP