What are the other Names for this Condition? (Also known as/Synonyms)

• African Eye Worm Infection
• Calabar Swellings
• Loa Loa Filariasis

What is Loiasis? (Definition/Background Information)

• Loiasis, or African Eye Worm Infection, is a type of parasitic infection caused by Loa loa. It is a vector-borne infection that is transmitted by an infected day-biting tabanid fly (deerfly or horse fly)
• The condition is endemic to many nations of west and central Africa. The infected individuals present itchy subcutaneous nodules on the upper and lower limbs, along-with other systemic symptoms
• A treatment of Loiasis involves the use of the antiparasitic medication diethylcarbamazine, which can result in a complete cure. Longstanding infections that remain untreated may result in severe complications

Who gets Loiasis? (Age and Sex Distribution)

• Loiasis infects all individuals, irrespective of age, gender, race, or ethnicity
• The disease is especially observed among people, who live in the tropical rainforest regions of Western and Central Africa, where Loiasis is endemic. These African nations include:
  • Angola
  • Benin
  • Cameroon
  • Central African Republic
  • Chad
  • Congo
  • Equatorial Guinea
  • Gabon
  • Nigeria
  • Uganda

What are the Risk Factors for Loiasis? (Predisposing Factors)

Following are the risk factors for Loiasis:

• Living in the tropical rainforest areas in west and central Africa, where Loiasis is endemic
• Travelers visiting the endemic regions, especially those who stay over several weeks to months, and receive multiple fly bites
• Staying close to rubber plantations (a higher density of deerflies are reported at these locations)
• Open spaces around residential settlements, especially where cooking is done using wood (the insects are attracted to wood smoke)
• A greater number of bites are recorded during the wet seasons
• Individuals with very weak immune system, such as those with HIV infection and AIDS, have a much higher risk for infection

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Loiasis? (Etiology)

Loiasis is a filarial disease (or filariasis) caused by the parasitic nematode Loa loa; nematodes are roundworms that may be transmitted from one host to another.

• Loiasis is caused by receiving repeated bites of the infected tabanid flies, specifically the deerfly/mango fly or horse fly belonging to the genus Chrysops (in particular Chrysops dimidiata and C. silicea)
• The flies bite during the daytime, injecting larval worms into the individual during a blood meal. These worms travel through blood and lodge within the subcutaneous tissues, where they develop into adults
• The adult worms reproduce and produce larva; the worms in their larval stage within a human host are known as microfilariae. Microfilariae are typically found in peripheral blood, but have also been observed in the sputum, urine, and cerebrospinal fluid
• The microfilariae travel via the lymphatic system to the lungs where they mainly reside. However, as part of their life cycle, these larval worms (non-adults) have to re-enter the tabanid flies
• The adult worms can move to several organs of the body, including the eyes, kidney, joints, apart from the lungs, and stay in the human hosts for several years (up to 17 years has been recorded)
• Humans are the primary hosts/reservoir for these parasites. Loa loa is transmitted from an infected individual to an uninfected individual through fly bites. The infection rates vary from between 10% to 70% (average 40%)

What are the Signs and Symptoms of Loiasis?

Studies have revealed that an individual has to receive multiple bites before the signs and symptoms of Loiasis can be manifested. Once an individual is infected, it may take about 4-6 months for the individual to present with the signs and symptoms of Loiasis. However, most infected individuals, who are permanent residents of the region, are known to remain asymptomatic. It is the migrants and travelers to the endemic areas that usually present symptoms.

The signs and symptoms may last for several months, and may include:

• Localized subcutaneous firm swellings, known as Calabar Swellings, typically present on the arms and legs, near the joints
• Numbness may be felt in the region
• Localized itching around these swellings or generalized body itching may be noted (even if there is no swelling)
• Sometimes, the adult worms may be seen moving beneath the skin
• Rashes on the body that resemble hives (itchy red spots)
• Muscle and joint pain
• Swollen limbs that may be transient
• Painful swelling of the lymph nodes
• Fatigue and tiredness
• Eye worms: Adult worms can be seen moving across the eye surface, resulting in eye pain, conjunctivitis-like symptoms, itchiness, and sensitivity to light. This event may last for a few hours or even up to 7 days; but, generally, the eye/vision remains unaffected
• In males, scrotal swellings may be observed

How is Loiasis Diagnosed?

A diagnosis of Loiasis would involve the following exams and tests:

• Complete physical examination with medical history evaluation (including history of recent travel)
• Assessment of the presenting signs and symptoms such as Calabar swellings
• Complete blood count (CBC) and peripheral blood smear; an increased level of eosinophils may be detected (peripheral eosinophilia)
• Blood tests to detect antibodies against the parasite
• Polymerase chain reaction (PCR) test
• Ophthalmologic (eye) exam
• Skin biopsy (of the subcutaneous nodules): A skin tissue biopsy is performed and sent to a laboratory for a pathological examination, who examines the biopsy under a microscope. After putting together clinical findings, special studies on tissues (if needed) and with microscope findings, the pathologist arrives at a definitive diagnosis
• Molecular test to detect the parasites can help confirm the diagnosis

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Loiasis?

Loiasis can cause any of the following complications:

• Severe emotional stress
• Cosmetic concerns
• Pleural effusion (fluid collection around the lungs); lung inflammation
• Scarring of the heart muscles; cardiomyopathy
• Swollen kidney (nephropathy)
• Mild damage to the brain (encephalopathy)
• Severe scratching of the skin can lead to secondary infections due to bacteria or fungus
• Loiasis can be a chronic and recurrent condition
• Individuals in the endemic region may also present co-infection with river blindness (or onchocerciasis), another parasitic roundworm infection occurring from bites of the female blackfly
• Treatment medication side effects, which can be severe in some cases

How is Loiasis Treated?

Loiasis is treated using antiparasitic medications which can bring about a complete cure. The treatment may last for a few weeks to months, depending upon the individual’s specific health condition. However, it is important to assess the load of microfilariae in blood (numbers/unit volume) and categorize the infection as light or heavy, prior to administration of medication.

• Diethylcarbamazine (DEC), an anthelmintic medication, is the treatment of choice
  • In individuals with light infection and presenting symptoms, DEC is prescribed for about 3 weeks
  • In individuals with heavy infection, albendazole is administered for a few weeks (or apheresis, an extracorporeal therapy to separate blood components is considered), prior to treatment with DEC
• Extraction of live adult worms from the eye
• Since the infection can be longstanding, periodic medical checkups and follow-up appointments are important and necessary

Note: Administering DEC directly to a heavily-infected individual may lead to coma and fatal encephalopathy. Also, prior to treating with DEC, an exclusion of river blindness is important to prevent any hypersensitivity (allergic) reaction that may aggravate the disease.

How can Loiasis be Prevented?

Loiasis is a vector-borne disease, which is preventable by avoiding the bite of the infected deerfly or horse fly. The following measures are useful in controlling transmission of the condition:

• Sleeping under insecticide-treated ‘mosquito nets’ is a highly recommended practice in endemic areas; also, one must avoid sleeping outdoors during the daytime
• Spraying the residence with DDT and other recommended insecticides
• Use of insect-repellent creams
• It is also advisable to cover the exposed arms and feet by wearing full-length pants, full-sleeved shirts, etc.
• Sprays containing permethrin can be used on clothes; sprays containing DEET can be used on the skin
• Deploying suitable vector control measures
• Individuals traveling from non-endemic regions to endemic regions have to be made aware of the risk factors and basic preventive methods
• Prophylactic administration of diethylcarbamazine to travelers and tourists to endemic regions, especially if the visit or stay is for an extended duration

What is the Prognosis of Loiasis? (Outcomes/Resolutions)

• Loiasis, with early detection and proper treatment using suitable medications (including completing the full course) is a completely curable infection, and the prognosis is typically excellent
• A lack of treatment or a delay in treating symptomatic individuals can lead to severe complications; the infections may also last for a long period of time

Additional and Relevant Useful Information for Loiasis:

• According to the World Health Organization (WHO), Loiasis is categorized as a “Neglected Tropical Disease”

According to WHO statistical reports, it is estimated that nearly 30 million people are at risk of infection in the endemic regions (African countries)