FILARIASIS (1)

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M.PRASAD NAIDUMSc, (Medical) Ph.D. (Medical)

• FILARIASIS 

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FILARIASIS
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• Filariasis (or philariasis) is a parasitic
  disease that is caused by thread-like roundworms b
  elonging to the Filarioidea type.
•  These are spread by blood-feeding black
  flies and mosquitoes.
• Eight known filarial nematodes use humans as
  their definitive hosts. These are divided into
  three groups according to the niche within the
  body they occupy.

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• Lymphatic filariasis is caused by the
  worms Wuchereria bancrofti, Brugia malayi,
  and Brugia timori.
• These worms occupy the lymphatic system,
  including the lymph nodes in chronic cases,
  these worms lead to the disease elephantiasis.

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• The adult worms, which usually stay in one
  tissue, release early larval forms known
  as microfilariae into the host's bloodstream.
• These circulating microfilariae can be taken up
  with a blood meal by the arthropod vector in the
  vector, they develop into infective larvae that
  can be transmitted to a new host.

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Morphology

• Adult worm
• Adult are minute,whitish thread like and are
  filariform in shape with smooth surface.
• Both the ends are tapering.

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• Individuals infected by filarial worms may be
  described as either "microfilaraemic" or
  "amicrofilaraemic", depending on whether
  microfilariae can be found in their peripheral
  blood.
• Filariasis is diagnosed in microfilaraemic cases
  primarily through direct observation of
  microfilariae in the peripheral blood.
• Occult filariasis is diagnosed in
  amicrofilaraemic cases based on clinical
  observations and, in some cases, by finding a
  circulating antigen in the blood.

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Male worm

• Male worm measures 40mm in length and and 0.1 mm
  in breadth.
• Posterior end is sharply curved ventrally with
  two spicules of unequal length.

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Female worm

• The female measures 80-100mm in length and are
  longer than males.
• The female are viviparous and lay eggs containing
  well developed embryos, the microfilariae.
• The microfilariae remain coiled together within
  the uterus and vagina of the mature gravid female
  worm.

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Microfilaria

• The third stage larva is called as microfilaria.
• Found in peripheral blood and often in the
  hydrocele fluid and chylous urine.
• They are transparent and colourless by a hyaline
  sheath.
• The microfilaria can live up to 70 days in the
  human blood.

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Microfilarial periodicity

• There is a marked periodicity in the circulation
  of microfilaria in the blood.
• They will be present in high numbers in the
  peripheral blood during a 4 hour period at mid
  night and scanty or absent at day time. This type
  of periodicity is called as nocturnal
  periodicity.
• The exact mechanism of periodicity is not clearly
  known.Body temperature,oxygen,sleeping habits etc
  may influence the periodic pattern of the
  microfilaria.

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• Third stage larva
• It is the infective form of the filarial worm for
  humans.
• It is found only in mosquito vectors.
• The microfilaria are elongated, filariform and
  measure 1.4mm to 2?m in length.

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Laboratory animal

• African green leaf monkeys.
• The adult worms are found in the
  sacral,para-aortic and inguinal lymph nodes and
  the thoracic duct and associated vessels.

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Life cycle

• Completes life cycle in two hosts.
• Definitive host
• Man.
• Intermediate host
• Mosquitoes
• Culex quinquefaciatus,
• Anopheles
• Aedes Species.

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Pathogenesis and clinical features

• The pathogenic effect is produced by adult worms
  of Wuchereria,living or dead.
• The infections are mainly classified into two
  forms
• 1.CLASSICAL FILARIASIS.
• 2.OCCULT FILARIASIS.

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Differences between classical and occult
filariasis
CLASSICAL FILARIASIS OCCULT FILARIASIS
Cause Devoloping worms and adult Microfilaria
Basic lesion Acute inflammation and epitheloid granuloma Eosinophilic granuloma
Organs involved Lymphatic system Lymphatic system, lung,liver and spleen
Microfilaria Present in blood Present in affected tissues
Therapeutic response No response Responds to microfilaricidal agent
Serological tests Complement fixation is not sensitive Highly sensitive
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Causes

• Human filarial nematode worms have complicated
  lifecycles, 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

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• In the intermediate host, the microfilariae molt
  and develop into third-stage (infective) larvae.
• Upon taking another blood meal, the vector
  insect 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.

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Filarial fever

• ? Filarial lymphangitis usually accompanied by a
  rise of temperature ranging from 1030 c to 104o F
  which may continue for several days.
• ? The temperature comes down with profuse
  sweating.
• ? The fever is associated with localised sign
  of inflammation of the lymphatic vessel where the
  adult worm lies.
• ? Examination of the blood may reveal
  microfilaria at this stage.

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Elephantiasis of leg
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Elephantiasis of Breast Scrotum
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Elephantiasis of the ingiuinal area
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Scrotal elephantiasis
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• The most spectacular symptom of lymphatic
  filariasis is elephantiasisedema with thickening
  of the skin and underlying tissueswhich 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.

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• However, different species of filarial worms tend
  to affect different parts of the body Wuchereria
  bancrofti can affect the legs, arms, vulva,
  breasts, and scrotum (causing hydrocele formation)
  , while Brugia timori rarely affects the
  genitals.Those who develop the chronic stages of
  elephantiasis are usually amicrofilaraemic, and
  often have adverse immunological reactions to the
  microfilariae, as well as the adult worms.

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• The subcutaneous worms present with skin rashes,
  urticarial papules, and arthritis, as well as
  hyper- and hypopigmentation macules. Onchocerca
  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.

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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
  finger tip larger veins can be used for blood
  extraction, but strict windows of the time of day
  must be observed.

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• Blood must be drawn at appropriate times, which
  reflect the feeding activities of the vector
  insects. Examples are W. bancrofti, 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.

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• Some filarial worms, such as M.streptocerca and O.
  volvulus, produce microfilarae 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.

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• 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
  amicrofilaraemic cases. Spot tests for
  antigen are far more sensitive, and allow the
  test to be done any time, rather in the late
  hours.

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• Lymph node aspirate and chylus fluid may also
  yield microfilariae. Medical imaging, such as CT
  or MRI, may reveal "filarial dance sign" in
  chylus 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. Xenodiagnosis is
  now obsolete, and eosinophilia is a nonspecific
  primary sign.

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Treatment

• The recommended treatment for people outside the
  United States is albendazole (a
  broad-spectrum anthelmintic) combined
  with ivermectin. A combination of
  diethylcarbamazine and albendazole is also
  effective. 
• All of these treatments are microfilaricides
  they have no effect on the adult worms. Different
  trials were made to use the known drug at its
  maximum capacity in absence of new drugs.

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• In a study from India, it has been shown that a
  formulation of albendazole has better
  anti-filarial efficacy than albendazole itself.
• In 2003, the common antibiotic doxycycline was
  suggested for treating elephantiasis

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• 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.
• Clinical trials in June 2005 by the Liverpool
  School of Tropical Medicine reported an
  eight-week course almost completely eliminated
  microfilaraemia

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Prevention and control

• 1.Mosquito control
• PhysicalMosquito net,effective drainage system.
• Chemical Mosquito repellents,DDT
• BiologicalGambusiya fish.
• 2.Treatment of the patients

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Spraying DDT
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Mosquito nets
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Gambusia fish
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Thank you