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Health Topics: / Filariasis

  1. a tropical disease caused by the presence of filarial worms, especially in the lymph vessels where heavy infestation can result in elephantiasis.

Filariasis is a disease group affecting humans and animals, caused by filariae; ie, nematode parasites of the order Filariidae.[1] Of the hundreds of described filarial parasites, only 8 species cause natural infections in humans. The World Health Organization (WHO) has identified lymphatic filariasis as the second leading cause of permanent and long-term disability in the world, after leprosy.

In lymphatic filariasis, repeated episodes of inflammation and lymphedema lead to lymphatic damage, chronic swelling, and elephantiasis of the legs (see the image below), arms, scrotum, vulva, and breasts .[2, 3, 4, 5, 6, 7]

Filariasis. Unilateral left lower leg elephantiasi
Filariasis. Unilateral left lower leg elephantiasis secondary to Wuchereria bancrofti infection in a boy.

Signs and symptoms

Lymphatic filariasis

  • Fever
  • Inguinal or axillary lymphadenopathy
  • Testicular and/or inguinal pain
  • Skin exfoliation
  • Limb or genital swelling - Repeated episodes of inflammation and lymphedema lead to lymphatic damage, chronic swelling, and elephantiasis of the legs, arms, scrotum, vulva, and breasts.

The following acute syndromes have been described in filariasis:

  • Acute adenolymphangitis (ADL)
  • Filarial fever - Characterized by fever without associated adenitis
  • Tropical pulmonary eosinophilia (TPE)

Onchocerciasis

The clinical triad of infection in onchocerciasis is as follows:

  • Dermatitis - Skin lesions include edema, pruritus, erythema, papules, scablike eruptions, altered pigmentation, and lichenification
  • Skin nodules (ie, onchocercomas) - Skin nodules tend to be common over bony prominences
  • Ocular lesions - Eye lesions are usually related to the duration and severity of infection and are caused by an abnormal host immune response to microfilariae; loss of visual acuity may occur

Loiasis

The diagnostic feature of loiasis is a Calabar swelling, ie, a large, transient area of localized, nonerythematous subcutaneous edema. This is most common around the joints.

Mansonella infections

These are usually asympt omatic. If symptoms are present, they may include fever, pruritus, skin lumps, lymphadenitis, and abdominal pain.

See Clinical Presentation for more detail.

Diagnosis

Microfilariae can be detected through examination of the following:

  • Blood - The microfilariae of all species that cause lymphatic filariasis and the microfilariae of Loa loa, Mansonella ozzardi, and M perstans are detected in blood [8]
  • Urine - If lymphatic filariasis is suspected, urine should be examined macroscopically for chyluria and then concentrated to examine for microfilariae
  • Skin - Onchocerca volvulus and M streptocerca infections are diagnosed when microfilariae are detected in multiple skin-snip specimens from different sites located on both sides of the body; the Mazzotti test allows a presumptive diagnosis of cutaneous filariasis to be made when skin snips are negative for microfilariae
  • Eye - Microfilariae of O volvulus may be detected in the cornea or anterior chamber of the eye using slit-lamp examination

The following imaging studies can be used in the evaluation of filariasis:

  • Chest radiography - Diffuse pulmonary infiltrates are visible in patients with TPE
  • Ultrasonography - Can be used to demonstrate and monitor lymphatic obstruction of the inguinal and scrotal lymphatics; has also been used to demonstrate the presence of viable worms
  • Lymphoscintigraphy [9]

Histologic findings include the following:

  • Lymphatic filariasis - Affected lymph nodes demonstrate fibrosis and lymphatic obstruction with the creation of collateral channels
  • Elephantiasis - The skin is characterized by hyperkeratosis, acanthosis, lymph and fatty tissue, loss of elastin fibers, and fibrosis
  • Onchocerciasis - Onchocercomas have a central stromal and granulomatous, inflammatory region where the adult worms are found and a peripheral, fibrous section; microfilariae in the skin incite a low-grade inflammatory reaction with loss of elasticity and fibrotic scarring

See Workup for more detail.

Management

Anthelmintics used in the treatment of filariasis include the following:

  • Diethylcarbamazine (DEC)
  • Ivermectin - Drug of choice for Wuchereria bancrofti
  • Suramin - Only drug in clinical use for onchocerciasis that is effective against adult worms
  • Mebendazole
  • Flubendazole
  • Albendazole

Surgery

In lymphatic filariasis, large hydroceles and scrotal elephantiasis can be managed with surgical excision. Correcting gross limb elephantiasis with surgery is less successful and may necessitate multiple procedures and skin grafting.

In onchocerciasis, nodulectomy with local anesthetic is a common treatment to reduce skin and eye complications.

Filariasis (or philariasis) is a parasitic disease caused by an infection with roundworms of the Filarioidea type.[1] These are spread by blood-feeding black flies and mosquitoes. This disease belongs to the group of diseases called helminthiases.

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:

·         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 syndrome of elephantiasis.

·         Subcutaneous filariasis is caused by Loa loa (the eye worm), Mansonella streptocerca, and Onchocerca volvulus. These worms occupy the subcutaneouslayer of the skin, in the fat layer. L. loa causes Loa loa filariasis, while O. volvulus causes river blindness.

·         Serous cavity filariasis is caused by the worms Mansonella perstans and Mansonella ozzardi, which occupy the serous cavity of the abdomen.

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.

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.

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.[2] 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; Wuchereria bancrofti can affect the legs, arms, vulva, breasts, and scrotum (causing hydrocele formation), while Brugia timori rarely affects the genitals.[citation needed] 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

The subcutaneous worms present with 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.[citation needed] 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 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. 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.

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. 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. 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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    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. 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.[7] 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.                                   Other animals

    Filariasis can also affect domesticated animals, such as cattle, sheep, and dogs.

    Cattle

    • Verminous haemorrhagic dermatitis is a clinical disease in cattle due to Parafilaria bovicola.
    • Intradermal onchocercosis of cattle results in losses in leather due to Onchocerca 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

    Dogs

    • Heart filariasis is caused by Dirofilaria immitis.

    • Treatment and prevention

      Treatment

      Treating endemic communities
      The primary goal of treating affected communities is to eliminate microfilariae from the blood of infected individuals in order to interrupt transmission of infection by mosquitoes.

      Studies have shown that a single dose of diethylcarbamazine citrate (DEC) has the same long-term (1 year) effect in decreasing levels of microfilaraemia as the formerly recommended 12-day regimen of DEC. More importantly, the use of single doses of two drugs administered together (optimally albendazole with DEC or ivermectin) is 99% effective in removing microfilariae from the blood for a full year after treatment. This level of treatment effectiveness has made feasible new efforts to eliminate lymphatic filariasis.

      Treating individuals
      The most significant advance in efforts to alleviate the suffering caused by elephantiasis has been the recognition that much of the progression in pathology is a result of bacterial and fungal “superinfection” of tissues, linked to compromised lymphatic function caused by earlier filarial infection. Rigorous hygiene of affected limbs combined with adjunctive measures to minimize infection and promote lymph flow dramatically reduce the frequency of acute episodes of inflammation (“filarial fevers”) and markedly improve the elephantiasis itself.

    • Prevention

      Avoidance of mosquito bites through personal protection measures or community-level vector control is the best option to prevent lymphatic filariasis. Periodic examination of blood for infection and initiation of recommended treatment are also likely to prevent clinical manifestations.

      Management of symptoms

      Relatively simple and well known surgical procedures are available to correct hydrocele. Because secondary bacterial infections play an important role in precipitating acute adenolymphangitis episodes and progression of lymphoedema, simple hygiene measures – either alone or in combination with antibiotic treatment – play an important role in preventing episodes of acute disease and in the management of lymphoedema. Daily washing of affected limbs with soap and safe water to prevent secondary infection, combined with simple exercises, elevation of the limb, and treatment of cracks and entry points, provides significant relief from acute episodes and slows progression of the disease.

      Podoconiosis
      Podoconiosis is a type of tropical lymphoedema resulting from a genetically determined abnormal inflammatory reaction to mineral particles in irritant red clay soils derived from volcanic deposits. It is mostly found in highland areas of tropical Africa, Central America and north-west India.

      It is a non-parasitic disease, and like lymphatic filariasis, results in impairments due to lymphodema. Like in the case for lymphatic filariasis, a basic package of care can alleviate suffering and prevent further progression of disease and disability.



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