Filariasis
Overview
Filariasis is a parasitic
disease caused by an infection with roundworms of the Filaricides type. These
are spread by blood-feeding insects such as black flies and mosquitoes. They
belong to the group of diseases called helminthiases.
These parasites exist in the
wild in subtropical parts of southern Asia, Africa, the South Pacific, and
parts of South America. One does not acquire them in temperate areas like
Europe or the United States.
Eight known filarial worms
have humans as a definitive host. These are divided into three groups according
to the part of the body they affect:
Lymphatic filariasis is
caused by the worms Washeterias Bancroft, Bruges Malay, and Brigida tamari.
These worms occupy the lymphatic system, including the lymph nodes; in chronic
cases, these worms lead to the syndrome of elephantiasis.
Subcutaneous filariasis is
caused by Loa loa (the eye worm), Manzanilla streptococci, and Onchocercid
volvulus. These worms occupy the layer just under the skin. L. loa causes Loa
loa filariasis, while O. volvulus causes river blindness.
Serous cavity filariasis is
caused by the worms Manzanilla perstans and Manzanilla ozzardi, which occupy
the serous cavity of the abdomen. Dirofilarial immitis, the dog heartworm,
rarely infects humans.
The adult worms, which
usually stay in one tissue, release early larval forms known as microfilariae
into the person's blood. These circulating microfilariae can be taken up during
a blood meal by an insect vector; in the vector, they develop into infective
larvae that can be spread to another person.
Individuals infected by
filarial worms may be described as either "microfilaremia", depending
on whether microfilariae can be found in their peripheral blood. Filariasis is
diagnosed in microfilaremia cases primarily through direct observation of
microfilariae in the peripheral blood. Occult filariasis is diagnosed in microfilaremia
cases based on clinical observations and, in some cases, by finding a
circulating antigen in the blood.
Signs and symptoms
The most spectacular symptom
of lymphatic filariasis is elephantiasis – edema with thickening of the skin
and underlying tissues—which was the first disease discovered to be transmitted
by mosquito bites. Elephantiasis results
when the parasites lodge in the lymphatic system.
Elephantiasis affects mainly
the lower extremities, while the ears, mucous membranes, and amputation stumps
are affected less frequently. However, different species of filarial worms tend
to affect different parts of the body; Washeterias Bancroft can affect the
legs, arms, vulva, breasts, and scrotum (causing hydrocele formation), while Brigida
tamari rarely affects the genitals. Those who develop the chronic stages of
elephantiasis are usually free from microfilariae (microfilaremia), and often
have adverse immunological reactions to the microfilariae, as well as the adult
worms.
The subcutaneous worms
present with rashes, urticarial papules, and arthritis, as well as hyper- and
hypopigmentation macules. Onchocercid volvulus manifests itself in the eyes,
causing "river blindness" (onchocerciasis), one of the leading causes
of blindness in the world. Serous cavity
filariasis presents with symptoms similar to subcutaneous filariasis, in
addition to abdominal pain, because these worms are also deep-tissue dwellers.
Cause
Human filarial nematode
worms have complicated life cycles, which primarily consists of five stages.
After the male and female worms’ mate, the female gives birth to live
microfilariae by the thousands. The microfilariae are taken up by the vector
insect (intermediate host) during a blood meal. In the intermediate host, the
microfilariae molt and develop into third-stage (infective) larvae. Upon taking
another blood meal, the vector insect, such as Culex pippins, injects the
infectious larvae into the dermis layer of the skin. After about one year, the
larvae molt through two more stages, maturing into the adult worms.
Diagnosis Filariasis is
usually diagnosed by identifying microfilariae on Giemsa stained, thin and
thick blood film smears, using the "gold standard" known as the
finger prick test. The finger prick test draws blood from the capillaries of
the fingertip; larger veins can be used for blood extraction, but strict
windows of the time of day must be observed. Blood must be drawn at appropriate
times, which reflect the feeding activities of the vector insects. Examples are
W. Bancroft, whose vector is a mosquito; night is the preferred time for blood
collection. Loa loa's vector is the deer fly; daytime collection is preferred. This method of diagnosis is only relevant to
microfilariae that use the blood as transport from the lungs to the skin. Some
filarial worms, such as M. streptococci and O. volvulus, produce microfilariae
that do not use the blood; they reside in the skin only. For these worms,
diagnosis relies upon skin snips and can be carried out at any time.
Concentration methods
Various concentration methods are applied:
membrane filter, Knott's concentration method, and sedimentation technique.
Polymerase chain reaction (PCR) and antigenic
assays, which detect circulating filarial antigens, are also available for
making the diagnosis. The latter are particularly useful in microfilaremia
cases. Spot tests for antigen are far more sensitive, and allow the test to be
done anytime, rather in the late hours.
Lymph node aspirate and chis fluid may also
yield microfilariae. Medical imaging, such as CT or MRI, may reveal
"filarial dance sign" in the chili’s fluid; X-ray tests can show
calcified adult worms in lymphatics. The DEC provocation test is performed to
obtain satisfying numbers of parasites in daytime samples. Xenodiagnoses is now
obsolete, and eosinophilia is a nonspecific primary sign.
Treatment
The recommended treatment for people outside
the United States is albendazole combined with ivermectin. A combination of diethylcarbamazine and
albendazole is also effective. Side effects of the drugs include nausea,
vomiting, and headaches. All of these
treatments are microfilaricides; they have no effect on the adult worms. While
the drugs are critical for treatment of the individual, proper hygiene is also
required. There is good evidence that albendazole alone; or addition of
albendazole to diethylcarbamazine or ivermectin, makes minimal difference in
clearing microfilaria or adult worms from blood circulation.
Diethylcarbamazine-medicated salt is effective in controlling lymphatic
filariasis while maintaining its coverage at 90% in the community for six
months.
Different trials were made to use the known
drug at its maximum capacity in absence of new drugs. In a study from India, it
was shown that a formulation of albendazole had better anti-filarial efficacy
than albendazole itself.
In 2003, the common antibiotic doxycycline
was suggested for treating elephantiasis.
Filarial parasites have symbiotic bacteria in the genus Wolbachia, which
live inside the worm and seem to play a major role in both its reproduction and
the development of the disease. This drug has shown signs of inhibiting the
reproduction of the bacteria, further inducing sterility. Clinical trials in June 2005 by the Liverpool
School of Tropical Medicine reported an eight-week course almost eliminated microfilaremia
non-primary source needed.
Society and culture
Research teams
In 2015 William C. Campbell and Satoshi Ōmura
were co-awarded half of that year's Nobel prize in Physiology or Medicine for
the discovery of the drug avermectin, which, in the further developed form
ivermectin, has decreased the occurrence of lymphatic filariasis.
Prospects for elimination
Filarial diseases in humans offer prospects
for elimination by means of vermicidal treatment. If the human link in the
chain of infection can be broken, then notionally the disease could be wiped
out in a season. In practice it is not quite so simple, and there are
complications in that multiple species overlap in certain regions and double
infections are common. This creates difficulties for routine mass treatment
because people with onchocerciasis in particular react badly to treatment for
lymphatic filariasis.
Other animals
Filariasis can also affect domesticated
animals, such as cattle, sheep, and dogs.
Cattle
Verminous hemorrhagic dermatitis is a
clinical disease in cattle due to Para filaria bovicola.
Intradermal onchocerciasis of cattle results
in losses in leather due to Onchocercid dermata, O. ochengi, and O. dukei. O.
ochengi is closely related to human O. volvulus (river blindness), sharing the
same vector, and could be useful in human medicine research.
Stenofilaria assamensis and others cause
different diseases in Asia, in cattle and zebu.
Horses
"Summer bleeding" is hemorrhagic
subcutaneous nodules in the head and upper forelimbs, caused by Para filaria multifarious
(North Africa, Southern and Eastern Europe, Asia and South America).
Dogs
Heart filariasis is caused by Dirofilarial imcites.
Jan Ricks Jennings, MHA, LFACHE
Senior Consultant
Senior Management Resources, LLC
412.913.0636 Cell
724.733.0509 Office
JanJenningsBlog.Blogspot.com
January 4, 2023
On May 7, 1996, the Charles
County Sheriff’s Office found the body of former CIA Director William E. Colby,
76, washed up on the shore of the Wicomico River near his canoe, about a
quarter mile from his country home on Cobb Island, Maryland. William Colby was born on January 4, 1920
and had a colorful and controversial career.
Colby’s death was ruled a drowning accident. Nine days earlier, he had
allegedly gone canoeing at dusk, never to return. Many people, including his family, believe he
was killed as a consequence of his service to the CIA. A graduate of Princeton University who
parachuted behind Nazi lines in France during World War II as a member of the
Office of Strategic Services (OSS) elite Jedburgh teams, Colby had spent most
of his adult life as a cold warrior in his country’s clandestine service, “a
soldier-priest,” as a colleague called him, on a covert crusade. He died at age 76.
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