Filariasis Paul R. Earl Facultad de Ciencias Biol

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FilariasisPaul R. EarlFacultad de Ciencias
BiológicasUniversidad Autónoma de Nuevo LeónSan
Nicolas, NL 664551, Mexicopearl_at_dsi.uanl.mx
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Six pathogenic species of nematodes (roundworms)
belonging to the superfamily Filarioidea develop
to the adult stage in humans. These and the
vectors are 1/Wuchereria bancrofti
Mosquito,2/Brugia malayi Mosquito,3/Brugia
timori Mosquito, 4/Loa loa Deerfly (Chrysops),
5/Onchocerca volvulus Blackfly (Simulium) and
6/Mansonella streptocerca Midge (Culicoides).
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The life cycles of the filarias are similar. Many
filarias parasitize wildlife. Dirofilaria immitis
of dogs and even cats, foxes and raccoons, known
as dog heartworm, is an example in domestic and
wild animals. Larvas (microfilarias) in the blood
of human hosts are ingested when the insect
vectors feed.
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One hundred and twenty million people in at least
80 nations of the world have lymphatic
filariasis. One billion people are at risk of
getting infected. Ninety percent of these
infections are caused by Wuchereria bancrofti,
and most of the remainder by Brugia malayi. For
W. bancrofti, humans are the exclusive host, and
even though certain strains of B. malayi can also
infect some felines and monkeys.
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New World countries with filariasis, likely
onchocerciasis, include Mexico, Guatemala, El
Salvador, Nicaragua, Honduras, Costa Rica,
Colombia, Ecuador, Brazil, Venezuela, Dominican
Republic, Haiti, Guyana, Suriname and Trinidad
Tobago. A typical case of lymphatic filariasis in
India is seen posteriorly.
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Onchocerciasis (river blindness) occurs in over
34 countries in Africa, Latin America and the
Arabian Peninsula. The vast majority of the
estimated 18 million persons infected with the
causative agent, the parasite Onchocerca
volvulus, live in Africa. Pockets of O. volvulus
in Mexico, Guatemala into Costa Rica are ignored
very effectively. A typical case in Brazil is
shown posteriorly.
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Microfilaria of Mansonella ozzardi.
Apparently, it died out of Campeche, Mexico.
Stain methylene blue.
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Life cycles. Mosquitoes and
flies are the usual vectors with mammals but even
frogs are filarial hosts.
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Simulium spp. The vector of
onchocerciasis in the old and New Worlds.
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Life cycle of Brugia that also applies to
Wuchereria by CDC
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Opening the dogs heart discloses adult filarias.
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Lymphatic filariasis in India.
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Clinical features. There are
chronic, acute and asymptomatic presentations of
lymphatic filarial disease, as well as some
syndromes associated with these infections. Among
chronic manifestations, hydrele, even though
found only with W. bancrofti infections not in
Brugia infections is the most common clinical
manifestation of lymphatic filariasis.
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Importation of black slaves from Africa to
colonies in the New World dictated the importaion
of Onchocerca volvulus, the cause of river
blindness. It occurs in southern Mexico,
Guatemala, El Salvador, Nicaragua, Honduras and
Costa Rica or in much of Central America and is
neglected by these countries that do not have the
political will to manage and in fact eradicate
tropical disease vectors.
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While lymphedema can develop in the absence of
overt inflammatory reactions and in the early
stages be associated with microfilaremia, the
development of elephantiasis (either of the limbs
or the genitals) is most often associated with a
history of recurrent inflammation. The early
pitting edema gives rise to a stronger edema with
the hardening of the tissues.
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Diagnosis. Until very recently,
diagnosing lymphatic filariasis had been
extremely difficult, since parasites had to be
detected microscopically in the blood, and in
most parts of the world, the parasites have a
nocturnal periodicity that restricts their
appearance in the blood to only the hours around
midnight.
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Treatment. Communities where
filariasis is endemic. The primary goal of
treating the affected community is to eliminate
microfilariae from the blood of infected
individuals so that transmission of the infection
by the mosquito can be interrupted.
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It is patently obvious that lymphatic filariasis
and also onchocerciasis should be eliminated in a
decade provided the determination is expressed.
The international and particularly the national
detractors do not want to spend the money. Note
also than subSahara Africa is deeply in debt, and
also India is seriously in debt just as it is a
true health problem.
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Treating the individual. Both albendazole
and DEC have been shown to be effective in
killing the adult-stage filarial parasites. It is
clear that this antiparasite treatment can result
in improvement of patients' elephantiasis and
hydrocele (especially in the early stages of
disease)
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WHO's Strategy to Eliminate Lymphatic
FilariasisThe strategy of the World Health
Organization (WHO) of the Global Programme to
Eliminate Lymphatic Filariasis has 2 aims a) to
stop the spread of infection (interrupt
transmission), and secondly b) to alleviate the
suffering of affected individuals.
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To interrupt transmission, districts in which
lymphatic filariasis is endemic must be
identified, and then community-wide ("mass
treatment") programs implemented to treat the
entire at risk population. In most countries, the
program will be based on once-yearly
administration of single doses of 2 drugs given
together albendazole plus either
diethylcarbamazine (DEC) or ivermectin, the
latter in areas where either onchocerciasis,
loiasis or another may also be endemic.
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To alleviate the suffering caused by the disease,
it will be necessary to implement community
education programmes to raise awareness in
affected patients. This would promote the
benefits of intensive local hygiene and the
possible improvement, both in the damage that has
already occurred, and in preventing the
debilitating and painful, acute episodes of
inflammation.
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The pledge in 1998 by GlaxcoSmithKline to
collaborate with the WHO in its elimination
efforts included the donation of numerous
resources, but especially albendazole free of
charge, for as long as necessary. This donation,
coupled with the recent decision by Merck to
expand its wellknown Mectizan (ivermectin).
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Immunologic notes. Schistosomiasis and
filariasis can of course be discussed together,
mainly because they are being simultaneously
eliminated in the same territories by
praziquantel, albendazole and invermectin. The
disease symptoms are mainly reactions to parasite
and related antigens. Then tests for surveillance
are needed for eradicated territories and others.
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Histologically, proliferation of lymphatic
endothelium can be identified, and the abnormal
lymphatic function associated with these changes
can be readily documented by lymphoscintigraphy.
Interestingly, all of these changes can occur in
the absence of overt inflammatory responses and,
even by themselves can lead to both lymphedema
and hydrocele formation.
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Economic and Social Impact. In recent years,
lymphatic filariasis has steadily increased
because of the expansion of slum areas and
poverty, especially in Africa and the Indian
subcontinent. More breeding sites are provided
for vectors, some at urban-civic interfaces. As
many filariasis patients are physically
incapacitated, it is also a disease that prevents
patients from having a normal working life.
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Lymphatic filariasis exerts a heavy social burden
that is especially severe because of the specific
attributes of the disease, particularly since
chronic complications are often hidden and are
considered shameful. For men, genital damage is a
severe handicap leading to physical limitations
and social stigmatization. For women, shame and
taboos are also associated with the disease.
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Histologically, proliferation of lymphatic
endothelium can be identified, and the abnormal
lymphatic function associated with these changes
can be readily documented by lymphoscintigraphy.
Interestingly, all of these changes can occur in
the absence of overt inflammatory responses and,
even by themselves can lead to both lymphedema
and hydrocele formation.
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However, filariasis, schistosomiasis, malaria
and other tropical diseases can be eradicated
by honest efforts, allowing
a better life for many.