Filariasis

Filariasis is caused by various species of parasitic nematodes known as filarial worms. In the Amazon, there are currently three species of filaria that infect humans: Mansonella ozzardi, Mansonella perstans, and Onchocerca volvulus (Portela et al., 2024).

Mansonella ozzardi and Mansonella perstans typically produce mild symptoms or may even be asymptomatic (Centers for Disease Control and Prevention). In contrast, Onchocerca volvulus is significantly more serious and can cause severe complications, including permanent blindness (Cleveland Clinic, "Onchocerciasis").

Historically, the Amazon also had cases of Wuchereria bancrofti, a species of filaria that causes lymphatic filariasis, also known as elephantiasis—a disease characterized by extreme and debilitating swelling of the limbs or genitals (Cleveland Clinic, "Elephantiasis"). However, Wuchereria bancrofti has now been eradicated from the Amazon region (Portela et al., 2024).

Because of this success, the greatest current concern is the vision loss caused by Onchocerca volvulus, a condition known as river blindness (Cleveland Clinic, "Onchocerciasis"). This parasite is primarily transmitted by blackflies from the genus Simulium, which breed near fast-flowing rivers (World Health Organization, 2025).

General symptoms of filariasis include itching, rash, and fatigue (CDC, 2024), but Onchocerca volvulus infections can cause ocular lesions, vision impairment, and in many cases, permanent blindness (Cleveland Clinic, "Onchocerciasis").

Onchocerca volvulus is believed to have originated in Africa (Dalten, Animal Diversity Web) and spread to the Americas via the transatlantic slave trade. While infection can be treated using a combination of ivermectin (which kills microfilariae) and doxycycline (which targets the symbiotic Wolbachia bacteria that help adult worms reproduce), existing blindness is irreversible (CDC, 2024).

References:

Portela, Cleudecir Siqueira. De Araujo, Claudia Patricia Mendes. Sousa, Patricia Moura. Simao, Carla Leticia Gomes. De Oliveira, Joao Carlos Silva. Crainey, James Lee. (2024) Filarial disease in the Brazilian Amazon and emerging opportunities for treatment and control Current Research in Parasitology & Vector-Borne Diseases Volume 5

https://www.sciencedirect.com/science/article/pii/S2667114X23000560#:~:text=Following%20the%20successful%20eradication%20of,Mansonella%20perstans%20and%20Onchocerca%20volvulus.

Mansonellosis Center for Disease Control and Prevention

https://www.cdc.gov/dpdx/mansonellosis/index.html#:~:text=In%20M.,been%20associated%20with%20corneal%20lesions.

Onchocerciasis (River Blindness) Cleveland Clinic

https://my.clevelandclinic.org/health/diseases/24868-onchocerciasis-river-blindness

Lymphatic Filariasis (Elephantiasis) Cleveland Clinic

https://my.clevelandclinic.org/health/diseases/elephantiasis

(January 29, 2025) Onchocerciasis World Health Organization

https://www.who.int/news-room/fact-sheets/detail/onchocerciasis#:~:text=Onchocerciasis%20is%20transmitted%20to%20humans,it%20bites%20an%20infected%20person.

Dalten, Mark. Onchocerca volvulus Animal Diversity Web

https://animaldiversity.org/accounts/Onchocerca_volvulus/

(May 13, 2024) Clinical Treatment of Onchocerciasis Center for Disease Control and Prevention

https://www.cdc.gov/filarial-worms/hcp/clinical-care/onchocerciasis.html#:~:text=The%20treatment%20of%20choice%20for,adult%20worm%20and%20for%20embryogenesis.