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CONTENTS
Introduction History of discovery Morphology Vector/Transmission Epidemiology Life cycle Incubation period Clinical Presentation Diagnosis Treatment Prevention
INTRODUCTION
Loa Loa is a blood dwelling Nematode that is parasitic to human beings.
The adult worm wanders through the subcutaneous tissue but is most obvious as it crosses the conjunctiva of the eye leading to its common name,the African Eye Worm.
Like all round worms it has separate male & female sexes.
Infection with loa loa is called Loiasis.
HISTORY OF DISCOVERY
Loa loa was first
described in 1770 by
a French Surgen,
Mongin,when he
unsuccessfully tried
to excise a worm
from the eye of a
woman in Santa
Domingo.
MORPHOLOGY
Adults worm range in length from 2 to
3.5 cm for males & 5 to 7 cm for
females. Both are not more than 0.5
mm wide.
Contd..
Nuclei as show below ,are found in the
tip of the tail & form a continuous row
without large spacing b/w nuclei
Contd..
Microfliaria are sheathed in a
cuticle.The sheath, however, dose not
stain with Giemsa. Microfilaria have a
diurnal periodicity to their
concentration in the blood stream.
VECTOR/ TRNSMISSION
Humans are infected by the bite of
deer fly(mango fly), chrysops which
deposit infective larvae on the skin .
The larvae enter the bite wound,
wander in the body & develop into
adults .The females release
microfilariae.
EPIDEMIOLOGY
The disease is found only in topical
central & west Africa,the habitat of
the vectors Chrysops.
LIFE CYCLE
1) Mango fly bites human,takes blood meal.Larvae are deposited on skin which enter in the bite wound.
2) Larvae develop into adult worms & wander through subcutaneous tissue.
3) Female release sheathed eggs called Microfilariae travel to the spinal fluid, blood, urine, sputum & lungs.
4) Mango fly bites human, takes blood meal containing microfilariae.
5) Microfilariae shed their sheaths & migrate to thoracic muscle of the fly.
Contd..
6) Microfilariae develop into larvae.
7) Further larval development.Infective
10-12 days after ingestion.
8) Larvae migrates to the fly’s mouth.
INCUBATION PERIOD
Microfilariae appear in the blood years
after the presence of the adult worm is
evident.
Incubation period 1 year (most typical)
to 10 years.
Contd..
Calabar Swelling :
A local edema of the subcutaneous
tissue,are caused by an allergic
reaction to dead worms or the metabolic
products of the worms. The swellings
are usually several inches in diameter &
subsides aftera few days to weeks.
They can be tender & painful.They can
occur anywhere on the body but mostly
on forearms & wrists.
COMPLICATIONS
May arise if worm lodges into unusual sites.Scrotal swelling , bowel obstruction ,endocarditis, arthritis, retinopathy, & neuropathy have all been seen in persons infected with loaloa.
Loa lao often increases the number of eosinophils , the immune cell that fights parastic infections, in blood.
Loa loa dose not cause serious long term damage to humans.
DIAGNOSIS
Calabar swelling & the presence of a
worm in the conjunctiva are main
diagnostic methods.
Laboratory test for elevated
eosinophils & C-reactive proteins can
also be formed.
Diagnosis is also made by
visualization of the microfilariae in a
blood smear.But its not reliable
because microfilariae might take years
to appear in the blood.
TREATMENT
Diethylcarbamazine eliminates the microfilariae & may kill adults.
Worms in the eyes reqiuresurgical excision by paralizing the worm with few drops of cocaine (4%).
PREVENTION
Prevention includes
avoiding contact with
the vector by bug
repellant,wearing long
sleeved clothing, &
sleeping in screened
areas. There is no
other known animal
reservoir outside
humans.