What Is Loiasis


A parasitic infection known as loiasis is native to the rainforest region of West and Central Africa, where it is spread by its vectors Chrysops silacea and C. dimidiata. Long thought to be innocuous, this illness has recently attracted a lot of attention since people with high Loa loa microfilariae burdens (> 8000 microfilariae per millilitre (mf/mL)) have experienced severe, even fatal, encephalopathy. 

Even though loiasis was the second or third most frequent reason for seeking medical attention in some parts of Africa, it has received significantly less research attention than the other two human filarial worm illnesses, onchocerciasis and lymphatic filariasis (LF). 152 million people reside in intermediate-risk areas with an estimated prevalence of roughly 30% (20-40%), while 144 million people live in high-risk zones, which are defined as locations where the estimated prevalence of eye worms is greater than 40%. We calculate that at least 10 million persons are infected with L. loa based on these numbers. The endemic nations include Angola, Cameroon, Chad, Equatorial Guinea, Gabon, Nigeria, the Republic of Congo, Sudan, and the Democratic Republic of the Congo.3 The second or third most frequent reason for medical visits in some endemic areas is loiasis. The bioecological zones that make up Cameroon, which is endemic for loiasis and is regarded as a miniature version of Africa, each have unique characteristics.

However, because it only occurs in Central Africa, loiasis is less common than onchocerciasis or LF and its most severe symptoms are uncommon or sneaky. 

Causes of loiasis

One of nine nematode worms that only inhabit humans is L.loa. It is widespread in West Africa, where prevalence rates can reach 50% in some places. Blood from an infected human is consumed by Chrysops flies, which are hosts of incomplete microfilaria maturation, to cause transmission. Then, infected flies vaccinate additional people. Once within the human body, the tiny worms known as microfilariae need several months to mature into adult worms. The microfilariae can travel to the body's tissues and specific organs, such as the lungs, as they develop. When the mature worms are inside, a movement in the eye or beneath the skin can be seen.

Signs and symptoms of loiasis

The range of symptoms and complications associated with loiasis ranges from the complete absence of symptoms to several severe complications, including neurological and psychiatric disorders, endomyocardial fibrosis, pulmonary infiltrates, renal complications, and cardiac complications. Many problems are commonly accompanied by pronounced eosinophilia and are likely caused by immune complex deposition. Additionally, one can experience, fatigue, and the entire body is itching. On the body, particularly close to joints like knees or elbows, there may be itchy, swollen spots or sores. These are known as swellings of Calabar. After a few days, the swelling may go away only to reappear days or weeks later. Joint or muscle discomfort. The worm moving under the skin. Conjunctiva, the line on the surface of the eye and inside your eyelid, is a worm that crawls over it.

Management and treatment for loiasis

Loiasis is treated with antiparasitic drugs like ivermectin and diethylcarbamazine (DEC). However, individuals with high blood levels of L. loa microfilariae may experience potentially fatal side effects from these drugs. Before administering DEC or ivermectin, a doctor may request a test to count the number of microfilariae in the blood. Ivermectin and DEC are not preferable if blood has more than 8,000 microfilariae per millilitre. In that case, a doctor can advise starting with a blood filtration treatment or the drug albendazole. Blood filtering and albendazole both help to reduce the amount of microfilaria in the system. Ivermectin or DEC might be safe for you to take at that point.

Diethylcarbamazine, which has been clinically tested in individuals with onchocerciasis and lymphatic filariasis, is the first-line treatment for loiasis recommended by the WHO.

Diethylcarbamazine use has frequently been linked to severe encephalopathy, especially in people with high loads of L. loa microfilariae, unlike the condition elicited by ivermectin in patients with high microfilaraemia. Any new drug designed to combat this infection must consider the likelihood of severe adverse effects caused by decomposing larvae because patients with high microfilaraemia are generally at high risk for them.


Rapid assessment procedures for loiasis, or RAPLOA, large-scale surveys with a short questionnaire for eye worm history were used to estimate the prevalence of L loa. Gabon and Equatorial Guinea, two of the ten countries with endemic L loa, were categorized as high risk due to their estimated prevalence of eye worm history being greater than 40% and their representation of a significant portion of the high-risk area in Africa. In Gabon, the RAPLOA survey was supplemented by microscope detection of microfilariae, and an overall prevalence of 66% for eye worm history and 22% for microfilaraemia was reported.

The detection of larvae (microfilariae), which are released by the adult worms into the peripheral circulation, can be used to diagnose an infection with L. loa along with the patient's history of an adult worm passing through the eye or itchy swellings on the body (Calabar swellings). Microfilariae and L loa-specific DNA can both be found in peripheral blood samples using microscopy and PCR testing, respectively. The search for L loa-specific antibodies in serum samples is another diagnostic tool. In general, loiasis is difficult to diagnose for two reasons. First off, there are many microfilariae in the blood between 1000 and 1600 hours. Therefore, a few hours window is the only time frame in which a reliable detection of parasites or chemicals linked with pathogens in peripheral blood is conceivable.

Second, there are adult worms present in more than half of the patients yet no microfilariae are ever found in the bloodstream. Lastly, microscopy and very sensitive and specific PCR have difficulty detecting these occult carriers.


How can I prevent loiasis?

There is no sure way to prevent loiasis. Nevertheless, measures such as consulting the expert before going to Loa Loa prominent places can be ensured. Mostly, avoiding exposure to warrant insect bites and using repellants must be followed.

How common is loiasis

It is challenging to assess the precise frequency of loiasis since it is frequently underreported and underestimated. However, compared to other tropical diseases, it is typically regarded as a comparatively uncommon illness. In some areas, including sections of Cameroon, the Democratic Republic of the Congo, Nigeria, and the Republic of Congo, it is endemic. Other nations that have heard about it include Angola, the Central African Republic, Gabon, Equatorial Guinea, and Sudan.

Who is at risk of loiasis?

People who live in or travel to areas where Loa loa is an endemic pest are at risk of contracting loiasis. 

What can I expect if I have loiasis?

The symptoms of loiasis include swelling, itching, lumps under the skin (Calabar swellings), redness and irritation of the eyes, exhaustion, headaches, pain in the muscles and joints, and fever. There's a chance of allergic responses. 

When should I see a doctor?

It is crucial to get medical assistance right once if you experience signs of loiasis or have recently visited a location where the disease is endemic, such as swelling, eye redness, itching, exhaustion, or allergic responses. A doctor can make an accurate diagnosis and choose the best course of action. Early action can ensure efficient control of the illness and help prevent consequences.


Loiasis is a parasitic infection originating from the rainforest region of West and Central Africa, spread by its vectors, Chrysops silacea and C. dimidiata. It is less common than onchocerciasis and lymphatic filariasis, with 152 million people in intermediate-risk areas and 144 million in high-risk zones. Loiasis is a parasitic infection that can cause severe encephalopathy in people with high microfilariae burdens (> 8000 microfilariae per millilitre). The disease is less common than onchocerciasis or LF, and its most severe symptoms are uncommon or sneaky.

Loiasis is treated with antiparasitic drugs like ivermectin and diethylcarbamazine, but individuals with high blood levels of L. loa microfilariae may experience potentially fatal side effects. Blood filtration treatment or albendazole can help reduce microfilariae levels in the body. Diethylcarbamazine is the first-line treatment for loiasis, but it has been linked to severe encephalopathy in people with high loads of L. loa microfilariae.

Rapid assessment procedures for loiasis (RAPLOA) were used to estimate the prevalence of L. loa in Gabon and Equatorial Guinea.

Diagnosis of loiasis is difficult due to the large number of microfilariae in the blood and the difficulty in detecting adult worms in the bloodstream. Detecting L. loa-specific DNA and antibodies in serum samples is another diagnostic tool.


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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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