Loiasis is a parasitic infectious disease caused by specific nematodes, Loa loa filariae, and manifests primarily by inflammatory, allergy-induced swelling reactions. An estimated 3 to 30 percent of the population is infected with Loa loa worms in the areas of distribution (West and Central Africa).
What is Loa loa?
Loiasis is the term used to describe infection with the nematode (nematode) Loa loa, which is transmitted by diurnal horseflies of the genus Chrysops and is primarily found in the tropical rainforests of West and Central Africa (Congo Basin). Approximately two to twelve months after infection with Loa loa, the parasite circulates in subcutaneous and connective tissues and occasionally in subconjunctival tissues (ocular tissues). Allergic reactions to the Loa loa worm result in sudden, itchy swellings of the skin (called calabar ulcers), especially on the face and legs, which persist for several days and may recur (return) at irregular intervals. If the larynx is affected by the Loa loa parasites, life-threatening glottic edema (acute swelling of the larynx) may manifest.
Causes
Loa loa is is a parasitic nematode (filarial) transmitted by infected diurnal horseflies of the genus Chrysops. Within the incubation period (2-9 months) in the infected human body, the horsefly-transmitted microfilariae (larvae of the Loa loa worm) mature into sexually mature adult filariae that live in the subcutaneous cellular tissue and connective tissue of the skin, mucous membranes, and possibly eyes and can migrate within these structures (so-called “migratory filariae”). The adult filariae also produce a large number of infectious microfilariae in the connective tissue, which enter the bloodstream during the day via the lymphatic system and circulate there. Allergically, the spread of the adult filariae as well as the microfilariae causes the inflammatory reactions and swellings characteristic of loiasis. If an infected human is bitten by a diurnal gadfly at this stage of the disease, the gadfly becomes infected and may transmit the infectious Loa loa microfilariae to other humans or great apes. In contrast, direct transmission of the Loa loa worm from human to human can be ruled out.
Symptoms, complaints, and signs
Loa loa, or loiasis, is a worm infection found in West Africa that mainly causes intensely itchy skin swellings. The swellings are soft and can produce bumps up to ten centimeters in size. In most cases, however, the bumps disappear again after two to three days, only to reappear elsewhere. Usually only one arm or foot is affected. In this case, the swellings represent allergic reactions of the body to the nematode. The migration of the nematodes also causes the swellings or bumps (Cameroon bumps or Calabar swellings) to migrate over the body. Although the disease is usually harmless. However, often a chronic course of more than ten years takes place, because the nematode is very long-lived. During this time, however, other organs such as the heart or kidneys can be affected. Thus, cardiac valve defects, renal insufficiency or even meningitis can possibly occur as late consequences. In rare cases, the crawling worm is also seen. This is especially true when it migrates through the eye. Because of this characteristic, Loa Loa is also called eye worm. Although the disease is very long lasting, it usually heals well after the worm dies. The worm can be surgically removed or killed with medication using diethylcarbamazine.
Diagnosis and course
Loa loa parasite infection can usually be diagnosed based on characteristic symptoms. The diagnosis of loiasis is confirmed by the detection of Loa loa microfilariae in the blood. The blood sample for the detection should be taken during the day, as the microfilariae have adapted to the diurnal gadfly as an intermediate host and therefore only circulate in the bloodstream at this time. In addition, an immunofluorescence test for the detection of infection antibodies as well as diethylcarbamazine (DEC), which triggers itching after a single administration and represents an indirect detection of the microfilariae, can be used.In the majority of cases, Loa loa infection is easily treatable and has a good prognosis. In rare cases, a prolonged course of loiasis may result in late complications such as endocarditis, meningoencephalitis, or renal damage.
Complications
Loa loa results in various symptoms and complications that can occur throughout the patient’s body. In most cases, this involves an allergic reaction of the body, causing the affected person to suffer from reddened skin or itching of the skin. Scratching usually only makes the itching worse. Especially on the face, the itching and redness can be very unpleasant for the affected person and lead to a lowered self-esteem. It is also not uncommon for the eyes to water and for eye pain to occur. Complications from Loa loa usually only occur if treatment is not received or if treatment is initiated very late. Patients can also suffer damage to the kidneys, resulting in renal failure in the worst case. The patient is then dependent on dialysis or a kidney transplant. Loa loa is treated with the help of medication. No complications occur in this process. It is not uncommon for those affected to appear tired and weary as a result of the disease and to no longer be able to actively participate in life. In most cases, however, a positive course of the disease is established.
When should one go to the doctor?
Swelling of the skin as well as itching are signs of an existing disease. If the symptoms persist for several days or weeks, a doctor should be consulted. If the itching leads to the development of open wounds, the affected person requires sterile wound care. If this cannot be sufficiently ensured, a doctor should be consulted. If pus forms or the affected body parts hurt, a visit to the doctor is necessary. The affected person is at risk of blood poisoning, which without medical care can lead to a life-threatening condition. If a formation of bumps is noticed, which recede independently after a few days and then reappear in another part of the body, the observations should be discussed with a doctor. In most cases, the diseased regions are located on the arms or feet of the patient. Without treatment, there will be long-term impairment of kidney function. Therefore, a physician should be consulted in the event of kidney dysfunction, urination complaints or changes in urine. If there are abnormalities in heart activity, changes in blood pressure or heart rhythm, the affected person needs a doctor. If there is a general feeling of illness, malaise, internal weakness or a decrease in usual performance, a visit to the doctor is also necessary.
Treatment and therapy
Loiasis is generally treated medicinally with diethylcarbamazine, an anthelmintic or vermifuge, which kills Loa loa microfilariae and, in some cases, adult filariae by interfering with the metabolism of the pathogens. Initially, a lower and successively increasing dosage is recommended, since the very high number of dying Loa loa parasites releases toxic substances that can cause pronounced allergic reactions such as rashes, asthmatic attacks, fever and fatigue in the human organism (so-called Mazzotti reaction). To inhibit or attenuate such allergic reactions and to reduce itching and inflammatory reactions, antihistamines or corticosteroids should be taken simultaneously. In some cases, other anthelmintics such as ivermectin or albendazole are used prior to diethylcarbamazine therapy. Diethylcarbamazine is contraindicated in the presence of pregnancy and in the concurrent presence of other parasitic infectious diseases such as Dirofilaria immitis or onchocerciasis due to allergic reactions triggered by the toxins released. The proteinuria (excretion of proteins in the urine) associated with diethylcarbamazine therapy in some cases of loiasis is usually transient. If Loa loa parasites are visible in the conjunctiva of the eye, they can be surgically removed under local anesthesia (sedation).
Outlook and prognosis
The prognosis of Loa loa depends on the time of diagnosis as well as treatment, but also on the basic course of the disease. In many cases, the pathogen has been in the organism for several months before clear health symptoms appear. For this reason, by the time it is detected, the worm may have spread and already caused internal damage. If the disease is detected at an early stage, drug treatment can be initiated. Normally, this leads to relief of the symptoms within a short time and subsequent freedom from symptoms. In the case of an unfavorable course of the disease, the first internal organ damage has already developed. In severe cases, renal insufficiency may occur. This represents a potential threat to human life. Often a donor organ is needed so that there is a prospect of recovery. Transplantation is complex and associated with numerous side effects. The donor organ is not always well received by the organism. Rejection reactions may occur, resulting in further deterioration of overall health. The prognosis is also worsened if a chronic course of the disease develops. Despite the administration of medication, there is a possibility that the pathogen is not completely killed. Therefore, it is not uncommon for therapy to be required for up to ten years.
Prevention
Because no vaccine exists against Loa loa to date, preventive measures are limited to exposure prophylaxis. These include wearing light-colored clothing that covers the skin and using repellents (sprays, creams, lotions to repel insects) and mosquito nets to protect against bites from horseflies infected with Loiasis.
What you can do yourself
If loasis is suspected, a doctor should be consulted first. A medical professional must clarify the disease and, if necessary, initiate treatment. Some self-help measures and various household and natural remedies support the healing process. Drug therapy can be supported by an active and healthy lifestyle. While in the first days after the illness, rest and bed rest still apply, after the acute phase, light sport may be practiced. Exercise in the fresh air strengthens the immune system and alleviates symptoms such as fatigue and asthma. If serious complications occur, the doctor must be informed. Loa loa is easily treatable, but close medical monitoring must still take place. Otherwise, secondary diseases may develop. Medicinal treatment can also be supported by a complaints diary. In this diary, the patient should record any side effects and interactions as well as the effects of the medication on skin rashes and other typical symptoms. With the help of these notes, the doctor can optimally adjust the medication and ensure a rapid cure. Accompanying this, re-infections must be prevented by taking the necessary precautions.
