Test 16  (ocular parasitology) 

 

Refer to the picture above for question 1, 2 & 3

1. This parasite is found in the following regions of the world:

a. Far East

b. South America

c. Southern Europe

d. South Africa

e. West Africa

Answera.F   b.T  c.F  d.F e.T
The picture shows Onchocerca volvulus, a nematode that causes onchocerciasis or river blindness. 
It is endemic in West AFrica, Middle East and Central and South America.

2. The vector for the parasite above is:
 

a	b
c	d
e.

Answera.F   b.F  c.T   d.F  e.F
The vector is the blackfly of the Simulium species ie. c.
a is a bug found in South America that transmit Chagas's disease.
b. is mosquito - malaria, yellow fever and Dengue fever
c. is sandfly - Leishmianiasis
e. is tsetse fly - sleeping sickness

3. Causes of blindness include:

a. trichiasis

b. keratitis

c. optic neuritis

d. chorioretinitis

e. chronic non-granulomatous iridocyclitis

Answera.F   b.T  c.T  d.T  e.T
The main cause of blindness is optic atrophy secondary to optic neuritis. Other causes can impair vision. Trichiasis is not a feature.

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Refer to the above picture for question 4, 5 & 6

4. The above patient has been doing some country walking recently,
     which pest(s) are likely to be the cause of this skin lesion:
 

a	b
c	d
e

Answera.F   b.T  c.F   d.T  e.F
The picture shows a typical lesion of Lyme disease erythema migrans with target-like rash.
b and d are deer ticks of the genus Ixodes. b shows
the ticks before and after feeding. d is the undersurface of the tick.
a is a wood tick
c is a flea
e is a pubic louse

5. The patient develops arthralgia and conjunctivitis a few weeks 
     later. Which organism is the most likely cause? :

a. 

b. 

c. 

d. 

e. 

Answera.T   b.F  c.F   d.F  e.F
It is caused by a spirochaete, Borrelia burgdorferi seen in a.
b is Streptococcus appearing as Gram positive string of cocci.
c. is Mycobacteria tuberculosis and appears as acid-fast bacilli
d. is candidas
e. is  Cryptococcal neoforman that has been stained with Indian Ink

 

6. The following are true about the ocular manifestations:

a. it is commoner in Europe than in North America

b. conjunctivitis is commoner than uveitis

c. the uveitis is typically non-granulatomatous

d. uveitis usually occurs in the first stage of the 
   disease

e. systemic antibiotic has no effect on the course of the 
   ocular disease
 

Answera.T   b.T   c.F   d.F   e.F
Ocular involvement appears to be commoner in the American version of Lyme disease.
Uveitis is uncommon whereas a self-limiting non-specific conjunctivitis is common in the first stage of Lyme disease.
The uveitis may be anterior, posterior or pan. The uveitis is often granulomatous and occurs in the second stage of the disease.
Antibiotic such as doxycycline is useful in treating Lyme disease and can improve the uveitis (which is treated with steroid). 
 

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