Parasites

Filariasis: A Brief Overview

Author Stephen A. Berger, MD , 07-Oct-2008

Filariasis is a parasitic infection caused by various species of filarial nematodes, which are transmitted to humans by blood-feeding arthropods. Filariasis is a parasitic disease caused by an infection with roundworms of the Filarioidea 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 US.

 

Eight known filarial worms have humans as definitive hosts. These are divided into three groups according to the part of the body they affect:

 

  • 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 known colloquially as “elephantiasis.”
  • Onchocerciasis is caused by Onchocerca volvulus and leads to intense itching and skin and eye damage.
  • Loaiasis is caused by Loa loa and leads to severe swelling under the skin; it is also known as “Calabar swellings.”

 

All these diseases are acquired through mosquito bites; there is no risk of acquiring filariasis through casual contact with an infected individual. Treatment for filariasis focuses on killing adult worms; this can be done through medication or surgery. In addition, measures should be taken to prevent mosquito bites, as this is the only way to acquire filariasis.

 

History

 

Like many diseases, filariasis has a long and storied history. The first documented cases dated back to the 19th century and were observed worldwide in tropical and subtropical regions. However, it is likely that the disease has been around for much longer than that. In fact, references to filariasis can be found in ancient medical texts and legends. 

It is clear that filariasis has been a part of human history for thousands of years. In the centuries since it was first documented, filariasis has become endemic in many parts of Africa, Asia, and South America. Today, the disease continues to pose a serious threat to public health. However, with early diagnosis and proper treatment, it is possible to manage the disease and reduce its impact on patients’ lives.

 

Epidemiology

 

Filariasis is primarily a disease of poverty and poor sanitation. It is estimated that more than 120 million people are infected with filarial nematodes worldwide, with approximately 40 million cases resulting in serious morbidity. The vast majority of affected individuals live in developing countries, where the disease is endemic. 

 

Filariasis in the Philippines

 

645,232 cases of filariasis (both forms) were estimated for the Philippines from 1963 to 1996.

 

Wuchereria bancrofti

  • Time and Place:
    • Bancroftian filariasis is endemic to southern Luzon, Mindanao, Mindoro, Palawan, Samar, Leyte, Sorsogon and Bohol.
    • 43 of 63 provinces were endemic n 1960; 45 of 77 provinces as of 1996 4; 290 municipalities as of 2001; 351 of 1,566 municipalities as of 2003; 39 of 79 provinces as of 2004.
    • Cases have recently been registered in Marinduque.
    • Both forms of filariasis (W. bancrofti and B. malayi) coexist in only four provinces: Davao Oriental, Palawan, Eastern and Northern Samar 6, and Surigao del Sur.
    • In 1984, 20 million persons were considered at risk for filariasis (both W. bancrofti and B. malayi) in the Philippines; 23.5 million in 2002; 15,034,765 in 2006; 21,882,581 in 2007.
    • Only two provinces (Marinduque and Sulu) were considered ‘high prevalence’ areas (>10%) as of 1993.
    • Disease in the Philippines is nocturnally periodic.
  • Prevalence surveys:
    • 37% of males and 17% of females in a village on Catanduanes (microfilaremia, 1978 publication)
    • 13% in Bayanan and 3.4% in Manganan (Mindoro, microfilaremia, 2004 publication)
  • Vectors:
    • The local vectors are Anopheles minimus flavirostris, Aedes poicilius , Culex quinquefasciatus, and Ochlerotatus (Finlaya) niveus.

 

Brugia malayi

  • Time and Place:
    • Brugia malayi infection is endemic to southwestern Palawan, Sulu, Agusan, and Samar.
    • Both forms of filariasis (W. bancrofti and B. malayi) coexist in only four provinces: Davao Oriental, Palawan, Eastern Samar, and Surigao del Sur.
    • Brugia malayi was first confirmed in the Philippines in 1964 – in Palawan (33.1% local prevalence at the time).
    • 43 of 63 provinces were endemic for filariasis in 1960; 45 of 77 provinces as of 1996. 1
    • In 1984, 20 million persons were considered at risk for filariasis (both W. bancrofti and B. malayi) in the Philippines.
  • Vectors:
    • The local vectors are Mansonia uniformis, Mansonia bonnea, and Mansonia dives.
    • Mansonia dives is associated with both nocturnally periodic and subperiodic microfilaremia patterns on Palawan.
  • Mass treatment with diethylcarbamazine and albendazole was administered to 1,945,121 persons in 2001.
    • 9,881,124 persons received mass treatment in 2005 ; 10,174,936 in 2006; 13,627,661 in 2007

 

Biology of the Disease

 

Filariasis is caused by various species of filarial nematodes, which are transmitted to humans by blood-feeding arthropods. The most common vectors of filariasis include mosquitoes and black flies. Once an individual is infected with filarial nematodes, the parasites migrate to the lymphatic system, where they mature and reproduce. 

 

Symptoms

 

The symptoms of filariasis vary depending on the stage and severity of the infection. In the early stages of infection, patients may experience:

  • Fever
  • Chills
  • Lymphadenopathy
  • pruritus. 

 

As the disease progresses, patients may develop lymphedema (swelling due to accumulation of lymph fluid), hydroceles (accumulation of fluid in the testicles), or elephantiasis (severe enlargement/swelling of body parts). These symptoms can be extremely debilitating and often lead to social isolation and stigmatization.

 

Diagnosis

 

Filariasis can be difficult to diagnose, as the symptoms may resemble those of other conditions. However, specific tests can be done to confirm the diagnosis. A blood test can detect the presence of the parasite, and an ultrasound can show blockages in the lymphatic system. 

Another way to diagnose filariasis is through a skin biopsy. This involves removing a small piece of skin and examining it under a microscope. The biopsy can help to confirm the presence of filarial worms. Finally, filariasis can also be diagnosed through a urine test. This test can detect the larvae of filarial worms in the urine. 

The diagnosis of filariasis is important because it can help guide treatment and prevent disease complications. Filariasis is a curable disease, but it often requires lifelong treatment. With proper care, people with filariasis can lead normal, healthy lives.  

Treatment

 

There is no cure for filariasis, but mass drug administration (MDA) with drugs such as ivermectin or albendazole can reduce transmission rates and lessen clinical symptoms. MDA programs are typically implemented at a community level by national health authorities. 

 

Prevention

 

The best way to prevent filariasis is to avoid exposure to mosquito bites or other potential vectors of transmission. When traveling to endemic areas, this can be done using mosquito nets or insect repellents. Additionally, good sanitation practices can help reduce exposure to FA vector breeding sites such as stagnant water bodies. 

 

Conclusion

 

Filariasis is a parasitic infection caused by various species of filarial nematodes, which are transmitted to humans by blood-feeding arthropods. The disease is characterized by immunological abnormalities and a wide range of clinical manifestations. Although there is no cure for filariasis, mass drug administration with drugs such as ivermectin or albendazole can reduce transmission rates and lessen clinical symptoms. The best way to prevent exposure to FA vector breeding sites such as stagnant water bodies is good sanitation practices that can help reduce exposure to mosquito bites or other potential vectors.

Author
Stephen A. Berger, MD

Stephen A. Berger, M.D. is affiliated with the Tel Aviv Medical Center, where he has served as Director of both Geographic Medicine and Clinical Microbiology. He also holds an appointment as Emeritus Associate Professor of Medicine at the University of Tel-Aviv School of Medicine. Dr. Berger co-founded GIDEON Informatics, developers of the GIDEON (Global Infectious Diseases and Epidemiology Online Network) web app, and the GIDEON series of ebooks.

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