Summary about Disease
Loiasis, also known as African eye worm, is a parasitic disease caused by the filarial worm Loa loa. It is transmitted to humans through the bites of infected deerflies or mango flies (genus *Chrysops*). The disease is endemic to rainforest areas of West and Central Africa. The adult worms migrate through subcutaneous tissues, sometimes visibly crossing the conjunctiva of the eye.
Symptoms
Calabar swellings: Localized subcutaneous swellings, often painful and itchy, that appear and disappear over days or weeks. These are the most characteristic symptom.
Eye worm: Visible migration of the adult worm across the conjunctiva of the eye, causing irritation, itching, and temporary blurred vision.
Generalized itching: All over the body, even without visible swellings.
Muscle pain: Aches and pains in the muscles.
Joint pain: Similar to muscle pain.
Fatigue: Feeling tired.
Urine discolouration (rare): Blood in urine.
Causes
Loiasis is caused by the filarial worm Loa loa. The worms are transmitted to humans through the bites of infected deerflies or mango flies (genus *Chrysops*). When a deerfly bites an infected person, it ingests microfilariae (larval stage of the worm). These microfilariae develop within the fly and become infective larvae. When the fly bites another person, the infective larvae are deposited onto the skin and enter the bite wound. They mature into adult worms within the human body.
Medicine Used
Diethylcarbamazine (DEC): The traditional drug of choice for treatment of loiasis. However, its use can be problematic in areas where Onchocerca volvulus* (another filarial worm causing river blindness) is co-endemic, as DEC can cause severe reactions in people with high *Onchocerca* microfilarial loads.
Albendazole: Can be used to slowly reduce the microfilarial load.
Ivermectin: Contraindicated due to the risk of severe adverse reactions, especially encephalopathy, in individuals with high Loa loa microfilarial loads.
Surgical Removal: Adult worms that migrate under the conjunctiva can be surgically removed.
Is Communicable
? Loiasis is not directly communicable from person to person. It requires transmission via the bite of an infected deerfly or mango fly.
Precautions
Insect repellent: Use insect repellents containing DEET or picaridin, especially during the day when deerflies are most active.
Protective clothing: Wear long-sleeved shirts and pants to minimize exposed skin.
Avoid peak biting times: Deerflies are most active during the day, particularly around midday.
Stay indoors: Remain indoors during peak biting times when possible.
Mosquito nets: While deerflies are day-biters and nets are primarily for mosquitoes, nets can provide some protection if used during the day.
Chemoprophylaxis: Prophylactic (preventative) treatment with DEC is available for travelers to endemic areas, but it must be used cautiously in areas where Onchocerca volvulus is also present.
How long does an outbreak last?
Loiasis does not typically occur in outbreaks in the same way as some viral or bacterial infections. It is an endemic disease in specific geographic regions. An individual infection can last for many years if untreated, as the adult worms can live for over a decade in the human body. The Calabar swellings will last days to weeks before subsiding.
How is it diagnosed?
Microscopic identification: Examination of blood samples for microfilariae. Blood samples should be collected during the day, as microfilariae exhibit diurnal periodicity (higher concentration in the blood during the daytime).
Identification of adult worm: Observation of the worm migrating across the eye.
Eosinophil count: Elevated eosinophil levels in the blood can be suggestive of parasitic infection.
Antibody tests: Available, but can have cross-reactivity with other filarial infections.
PCR: Molecular diagnostic tests (PCR) are available in some research settings for detecting Loa loa DNA.
Timeline of Symptoms
Incubation period: Months to years between the infective bite and the appearance of symptoms.
Early symptoms: May be mild and nonspecific, such as itching or fatigue.
Calabar swellings: Appear intermittently, lasting for days to weeks, with symptom-free intervals.
Eye worm: Sudden appearance of worm in the eye, lasts until the worm moves on or is removed.
Untreated infection: Can persist for many years, with ongoing Calabar swellings and potential for other complications.
Important Considerations
Co-infection: Loiasis often co-exists with other filarial infections, particularly Onchocerca volvulus*. This is critical because treatment with DEC can be dangerous in individuals with high *Onchocerca* microfilarial loads.
Pre-treatment assessment: Before starting DEC treatment, it is essential to assess the individual's risk for severe adverse reactions due to Onchocerca co-infection. Rapid assessment procedures for *Loa loa* endemicity exist to guide mass drug administration.
Travel history: A detailed travel history is important for diagnosis, especially in individuals from non-endemic areas.
Geographic location: Loa loa is localized to specific regions.
Severe adverse events: Can result in neurological issues, like encephalitis.