Filariasis

            Filariasis refers to infections caused by parasitic nematodes known as filarial worms. In the Brazilian Amazon, three principal human filarial parasites remain endemic: Mansonella ozzardi, Mansonella perstans, and Onchocerca volvulus. Other filarial worms normally associated with animals can occasionally infect humans, so these three do not represent every possible filarial infection in the region. Portela et al., 2024

            Mansonella ozzardi and Mansonella perstans cause mansonellosis. Many infections produce no symptoms, while reported symptoms include itching, fever, headache, and joint pain. However, these parasites should not be dismissed as completely harmless: M. ozzardi infections have been associated with corneal lesions in Brazil. Researchers also face difficulties determining whether some reported symptoms result from mansonellosis or other infections occurring alongside it. CDC, “Mansonellosis”

            The insect responsible for transmission depends on the parasite. Mansonella perstans is transmitted by biting midges, primarily from the genus Culicoides. Mansonella ozzardi can be transmitted by biting midges or blackflies, depending on the location. CDC, “Mansonellosis”

            Historically, the Brazilian Amazon also had transmission of Wuchereria bancrofti, which causes lymphatic filariasis. This mosquito-borne infection damages the lymphatic system and can cause severe swelling and disability. Advanced disease can produce elephantiasis. Brazil achieved interruption of transmission in 2017, and in 2024 the World Health Organization validated its elimination of lymphatic filariasis as a public health problem. Continued surveillance remains necessary. Portela et al., 2024; WHO, 2024

            Onchocerca volvulus causes onchocerciasis, also known as river blindness. It is transmitted by infected blackflies of the genus Simulium, whose larvae develop in fast-flowing rivers and streams. Remaining transmission in the Americas is concentrated in a remote area along the Brazil–Venezuela border, primarily affecting Indigenous Yanomami communities. WHO, “Onchocerciasis”; Portela et al., 2024

            Adult worms live beneath the skin, often within nodules, and produce microscopic offspring called microfilariae. These migrate through the skin and eyes. Inflammation, particularly when microfilariae die, can cause intense itching, skin changes, and eye damage that may progress to permanent blindness. Blindness is a possible complication, rather than an inevitable outcome of infection. WHO, “Onchocerciasis”

            Ivermectin is the main treatment for onchocerciasis. It kills microfilariae, helping reduce skin symptoms and prevent further eye damage, but does not kill adult worms, so repeated treatment is necessary. Doctors may also prescribe doxycycline, which targets the symbiotic Wolbachia bacteria that adult worms depend on. This can help kill adult worms. Treatment can prevent additional damage, but cannot restore vision already lost to permanent injury. CDC, “Clinical Treatment of Onchocerciasis”; CDC, “Treatment of Onchocerciasis”

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.