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Lymphatic filariasis

By: invivo

Lymphatic filariasis is the cause of elephantiasis and poses a risk for a billion people throughout the world. More than 120 million people suffer from it, 40 million of which are severely incapacitated or deformed. One third of bearers live in India, another third in Africa and the rest in Asia, the West Pacific and the Americas.

Usually contracted during childhood and endemic in more than 80 countries, filariasis is a chronic disease that can seriously injure patients. It is the cause of both chronic and acute infections and can be incapacitating. Besides increasing costs for the health system, patients face not only the limitations posed by the disease, but also social prejudice.

In Brasil, filariasis is endemic in only three state capitals: Belém, Manaus and Recife. In the first two cities, there has been a significant reduction in disease prevalence. In Recife, the Brazilian city with the largest number of cases, the Aggeu Magalhães Research Center (a Fiocruz national reference center for the control of filariasis) has been mapping the disease risk areas.

The adult filaria

The adult filaria

Causative agent

Filariasis is caused by a long and thin nematode (worm) called Wuchereria bancrofti, the only agent to cause the disease both in Africa and the Americas. The other pathogens are Brugia malayi (in China, Southeast Asia, Indonesia, the Philippines and Southern India) and Brugia timori (on Timor Island)

Transmission

In Brazil, filariasis is transmitted exclusively through the bite of the female mosquito Culex quinquefasciatus. A few species of the genus Anopheles also transmit Wuchereria bancrofti. Vectors for Brugia malayi and Brugia timori are from the genus Mansonia.

The disease

The incubation period for filariasis is between 9 and 12 months. Half of infected individuals in endemic areas develop the asymptomatic form of the disease, and, despite being healthy, they have microfilaria in their blood.

Who/TDR/Chandran

Who/TDR/Chandran

The first symptoms are usually inflammatory processes (triggered by the death of an adult worm) in the lymphatic ducts (lymphangitis) such as fever, chills, head aches, nausea, pain, sensitivity and redness along the lymphatic duct. These occur in different regions of the body, such as the scrotum, spermatic cord, breasts, legs, etc. Repeated onsets of lymphangitis and lymphadenitis (inflammation in lymph nodes) and genital lesions are also common.

Filariasis progresses slowly. Its signs and symptoms are mainly a consequence of the dilation (ectasia) of the lymphatic duct, which is often complicated by secondary infections. Between 10 and 15% of filariasis cases present elephantiasis after 10 to 15 years of infection.

Elephantiasis is caused by fibrosis (hardening and thickening) and hypertrophy (exaggerated swelling) of areas with lymphatic edema, and leads to deformation. Generally, it is located in one or both legs, or in external genitalia, and only rarely in breasts.

Filariasis is not the direct cause of elephantiasis. Several factors, such as the lack of hygiene of affected members, cause the proliferation of bacteria and the onset of an acute infection. Researchers have observed that simply cleaning the infected areas - such as the legs and scrotum - with water and soap is enough to prevent elephantiasis.

Treatment
The current drug used in the treatment of filariasis is called diethylcarbamazine. In countries where the disease coexists with onchocerciasis, invermectin is the drug of choice. In specific cases of resistance to the clinical treatment with drugs, the surgical removal of the adult worm is also indicated.

OMS Campaign

OMS Campaign

Prevention and control

• Treatment of infected individuals to eliminate microfilaria from the blood, thus preventing transmission. The World Health Organization recommends mass treatment of risk populations with an annual dose of diethylcarbamazine in high prevalence areas);
• Treatment of the sick;
• Promotion and dissemination of simple hygiene techniques through community education of patients with lymphedema, thus avoiding bacterial infections and the development of the more severe forms of the disease;
• Fighting the vector insect.

See also:

The history of filariasis

Sources:

World Health Organization

Tropical Disease Research/WHO

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