Loa loa

Loa loa is a parasitic worm that is transmitted to humans through the bite of a deer fly or mango fly, which are the primary vectors. This condition, known as loiasis, or African eye worm, primarily affects residents and visitors to West and Central Africa. Loa loa is one of the three main filarial nematode species that cause disease in humans, the others being Wuchereria bancrofti and Brugia malayi, which cause lymphatic filariasis.

Transmission

The life cycle of Loa loa involves two hosts: humans, where the adult worms mature, and the deer or mango flies, which belong to the genus Chrysops. The transmission cycle begins when a person is bitten by an infected fly. During the blood meal, the fly introduces the larval stage of the worm, known as microfilariae, into the human host. These larvae then migrate through the host's body, maturing into adult worms over several months. Adult worms can live up to 17 years within the human host.

Symptoms and Diagnosis

The presence of Loa loa in the human body can cause a variety of symptoms, ranging from mild to severe. Common symptoms include localized swellings known as Calabar swellings, itching, hives, and fatigue. One of the most notable symptoms is the migration of the adult worm across the eye, which can be seen moving under the skin or across the conjunctiva of the eye, leading to the common name "African eye worm."

Diagnosis of loiasis is typically made through the detection of microfilariae in the blood, although this can be challenging due to the periodicity of the microfilariae's appearance in the bloodstream. Other diagnostic methods include imaging techniques to visualize adult worms and serological tests to detect antibodies or antigens related to Loa loa.

Treatment

The treatment of loiasis involves the administration of antiparasitic medications, with diethylcarbamazine (DEC) being the drug of choice. However, treatment must be approached with caution, as killing the worms can lead to severe allergic or inflammatory reactions, especially in individuals with high worm burdens. In some cases, surgical removal of adult worms may be necessary, particularly when they migrate across the eye.

Prevention

Preventive measures against Loa loa infection are primarily aimed at reducing human contact with the vector flies. This includes wearing protective clothing, using insect repellent, and avoiding exposure in endemic areas during peak biting times of the flies. There is currently no vaccine available for loiasis.

Epidemiology

Loiasis is endemic to rainforest and swamp regions of West and Central Africa. The disease affects millions of people in these areas, with certain communities having a high prevalence of infection. The distribution and prevalence of loiasis are closely tied to the habitat of the Chrysops flies, which are the sole vectors of Loa loa.

Public Health Impact

The public health impact of loiasis is significant in endemic regions, where it can cause considerable morbidity. While the disease is not typically fatal, it can lead to chronic discomfort, social stigma, and economic hardship for affected individuals. Additionally, the presence of Loa loa can complicate the mass administration of drugs aimed at controlling other filarial diseases, such as onchocerciasis and lymphatic filariasis, due to the risk of severe adverse reactions.