filariasis

Filariasis: description

The term filariasis refers to a group of diseases in which small parasitic nematodes (filariae) are transmitted to humans through an insect bite (mosquitoes, brakes). Depending on the type of worm, the worms migrate from the blood to different target tissues, where they multiply. Divide the filarioses into three groups:

• lymphatic filariasis: The worms live especially in the lymphatic vessels
• Subcutaneous filariasis: The worms live directly under the skin
• Serous filariasis: The worms colonize the abdomen or chest

The World Health Organization (WHO) considers the filarioses to be neglected tropical diseases. Thus, it refers to diseases that have not received sufficient scientific and medical attention – often because of lack of financial support. However, “neglected” does not mean that they are rare or harmless.

The filariasis occurs mainly in tropical countries (especially tropical Africa, Southeast Asia, South America, Central America, Caribbean). In Germany, filariasis does not occur, but travelers may be affected. It is estimated that around 200 million people worldwide are infected with filaria.

Life cycle of the filaria

The filariae are worms from the tribe of nematodes (nematodes). Of the many hundreds of filaria species, only eight species of worms attack humans. In humans, larvae transmitted by the mosquito develop adult (adult) worms. There they mate and so-called females develop microfilariae, which then spread through the bloodstream throughout the body. The microfilariae have this name because they are usually only several hundred microns (millionths of a meter) in size and are visible only under the microscope.

In technical language, man is called the main host, because the multiplication of the parasite takes place in man. Mosquitoes and brakes are the secondary host, so they are only important to guarantee transmission to humans. Because after mating the released microfilariae are taken by the sting of a bloodsucking insect and develop in its organism to larvae, which are then passed on to the next people at the next blood meal.

Lymphatic filariasis

Lymphatic filariasis is the most common form of filariasis with about 120 million infected people worldwide. The larvae, which enter the human body after a mosquito bite, develop into worms, which settle in the lymphatic vessels. Most of the worms are in the lymphatic vessels of the legs, but sometimes also in the chest, the arms or in the genitals. Since the lymphatic vessels are clogged by the colonization and there is an ongoing inflammatory reaction, the lymphatic drainage is disturbed. Thus, over years, an increasing swelling of the affected body part develops. The worms always trigger new inflammatory reactions and damage the lymphatic system considerably.

After years, the swelling does not go back at all and it is called an “elephantiasis”. The name describes the enormously enlarged leg circumference of the affected person. The chronic lymphatic blockage significantly damages the tissue: The skin becomes wrinkled and hard, the tissue structure is severely altered and scarred connective tissue penetrates the subcutaneous tissue. According to the World Health Organization (WHO), lymphatic filariasis is the second leading cause of long-term disability worldwide. However, as the disease only becomes visible as “elephantiasis” after months to years without adequate medical treatment, it is rarely seen in Western Europe.

For the lymphatic filariasis (elephantiasis), three types of filari are possible:

• Wuchereria bancrofti (responsible for about 90 percent of the diseases, occurrence in Africa and Asia)
• Brugia malayi (especially in South and Southeast Asia)
• Brugia timori (especially in southeastern Indonesia)

Since the worms can survive many years in the lymphatic vessels, an infected person forms a permanent reservoir of microfilariae. The transmission of lymphatic filariasis occurs through the bite of various mosquito species, including the Aedes and the Anopheles mosquito. These also pass on the pathogens of yellow fever and malaria. Other carriers of filariasis are Culex and Mansonia species. It takes one to two years for the worms to become mature, sexually mature and produce microfilariae after infection. Therefore, the infection is often discovered very late or not at all.

Subcutaneous filariasis

Subcutaneous filariasis distinguishes two major diseases:

• Loa loa filariasis
• Onchocerciasis (river blindness)

Loa loa filariasis

Loa Loa is a filarial disease that is particularly prevalent in Central and West Africa. Currently, about twelve million people are infected. The disease is also called Cameroon bulge or Calabar swelling in some areas. The disease is transmitted by braking. The brakes of the Chrysops genus live especially in wooded areas, preferably on rubber tree plantations. They are diurnal and are attracted by human movements and log fires. Especially during the rainy season you should protect yourself from this type of brake.

In the sting Loa Loa larvae are transferred to the tissue under the skin. As with all filarial diseases, worms develop from the larvae, which then mate and excrete microfilariae. On average, it takes a year for the adult worm to develop. It lives and moves under the skin, and can sometimes be seen on the fingers, breasts or conjunctiva in the eye. Since the worm can be observed there very impressively and often wanders up there, he is colloquially “African eye worm” called. The worm moves at a speed of about 1cm / min, giving you plenty of time to watch it.

Onchocerciasis (river blindness)

The trigger of onchocerciasis is the filarie Onchocerca volvulus. A special course of onchocerciasis is the so-called river blindness. Onchocerciasis is transmitted through the black flies. The illness carries its German name, because the illness concerns above all humans, who live near rivers and are thus exposed to the likewise there increasingly occurring Kriebelmücke.

After the sting, the larvae of the onchocerciasis pathogen enter the subcutaneous tissue, where they then develop into the adult worm. Also in this filariasis, the worms excrete microfilariae, which are taken up by the insect in a new Kriebelmückenstich and infect other people.

Unlike most filarioses, the microfilaria do not enter the blood, but remain in the tissue under the skin. Over years, the microfilariae slowly rise from the legs to the remaining parts of the body. This leads to various inflammatory reactions, including in the cornea of ​​the eyes. If this is not treated, it leads to blindness of those affected.

The disease is particularly native to Central Africa. It also occurs in some areas of South America. Colombia and Ecuador are now onchocerciasic after efficient health programs. Worldwide, approximately 37 million people are infected.

Serous filariasis

The most important causative agent of serous filariasis is the worm Mansonella perstans. He occurs in Central Africa and South America. Since the symptoms are not clear, this disease is difficult to recognize and not very well known. Also, there is no organized program to curb transmission. However, there are several hundred million people infected worldwide. In some areas, the probability of becoming infected at some point during life is nearly 100 percent.

The parasite can be transmitted by various mosquito species, and migrates into the lung cavity, the heart or the abdomen. There, the worms mate and new microfilaria arise, which are taken in a new mosquito bite from the blood of the patient.

Filariasis: symptoms

The symptoms of Filariosen can be very different, because the parasites differ in their life cycles. It often takes months or even years before symptoms appear and an infection is even noticed. In some cases, no or only mild symptoms occur and the person lives with the worm for a lifetime, or gets infected again and again. Europeans are usually threatened by an infection only on longer trips to the tropics. If appropriate complaints occur, as a patient you should always draw the attention of the doctor to past travel activities.

Lymphatic filariasis:

In the case of lymphatic filariasis, the symptoms first appear after three months. Some people have little symptoms at the beginning, others complain of acute symptoms. Possible early signs of lymphatic filariasis are:

• Fever episodes (“filarial fever”)
• Inflammation and swelling of the lymph nodes
• increased number of certain immune cells in the blood, the so-called eosinophilic granulocytes

The adult worms move the lymphatic system and trigger recurring inflammation of the lymphatic vessels and lymph nodes (lymphangitis, lymphadenitis). The constant swelling causes typical skin changes of the chronic form of the lymphatic filariasis, which is therefore also called elephantiasis.

Elephantiasis is the result of a long-standing lymphatic filariasis. It forms massive swelling of the legs, the genitals or other body parts. The skin becomes rough and rough. Once the disease has progressed so far, it can only be treated in a very limited way.

In addition to the changes in the extremities, elephantiasis also damages the lungs. If this is impaired in its function, long-term damage also occurs in many other organs. The chronic lung disease is particularly evident in nocturnal asthma attacks, recurrent attacks of fever and increased pressure in the pulmonary arteries (pulmonary hypertension = pulmonary hypertension).

Since the lymphatic vessels have an important function for the immune system, the worms disturb the normal function of the immune system. As a result, other pathogens such as bacteria and fungi easier game to trigger an additional infection (secondary infection).

Full education in elephantiasis is rare in Europe and is usually observed only in emerging and developing countries.

Subcutaneous filariasis:

In subcutaneous filariasis, the worms colonize the skin and underlying tissue. Itching is often the main symptom, swelling and bumps are frequent companions.

Loa Loa:

Often, the infected in this form, except for occasional itching no complaints. In different parts of the body, the typical “Calabar bump” can develop. It is a local, sudden swelling that persists for one to three days. This is usually not very painful, it itches but strong. In addition, the spot can be slightly reddened. It occurs preferentially on the forearms, the back of the hand and on the face, but can also arise on other parts of the body. The bump does not have to heal completely, but can also persist as a small skin lift. The bump arises as a reaction of the immune system to the worm and its excretions.

Onchocerciasis (river blindness):

The adult (adult) worms form tangles under the skin, which are palpable from the outside as a painless knot. Such a worm-filled cutaneous knot is called an onchocercus. The adult worms consistently produce larvae, also referred to as microfilaria, in the skin nodes during their maximum fourteen-year life.

These microfilariae migrate from the skin knot into adjacent sections of the skin and, in principle, almost every area of ​​the body (microfilaria migration). If they are not caught by an insect by a sting, they will die after about six to 30 months. The dead microfilaria trigger a reaction of the immune system and thus complaints.

The patients complain of a strong itching, the skin becomes inflamed and the skin may thicken like leather (lichenification). The skin color (pigmentation) can disappear in some places, creating a kind of “leopard skin pattern”. In the long term, the entire skin of the body changes and one speaks of so-called “paper or senile skin.”

If microfilaria migration leads to inflammation of the cornea in the eye, it becomes cloudy. First, snowflake-like visual disturbances arise. With complete clouding of the cornea, light and dark can only be perceived. Typically, however, especially the conjunctiva of the eye is affected, in which a worm can sometimes live for years. Therefore, Loa Loa is often referred to as an eye worm.

More recently, studies suggest that there may be a possible link between worm infections and a disease that has only been explored for several years. The so-called “head nodding syndrome” is a special form of epilepsy that occurs in children in Uganda and southern Sudan. Food or cold can cause an epileptic seizure in this condition. This disease is related to the parasite “Onchocerca volvulus”. Exact background to the origin of the disease are not yet known.

Serous filarioses:

Most people have no complaints with a serous filariasis. As symptoms of this form are generally not dangerous and do not result in disability, serous filariases have been less extensively studied than the other filariases.

If symptoms occur, they usually occur in connection with the worm’s migration through the body. Bumps on the skin, which are reminiscent of the Calabar swelling of Loa Loa’s disease, may temporarily develop. In some cases, the infestation also triggers inflammation of the heart, lungs or organs in the abdomen. Occasionally, this worm also gets to the eye and it comes to pain or blurred vision. Since the worm is often found in East Africa, one speaks of the “Uganda eye worm”.

Filariasis: causes and risk factors

The different filarioses are transmitted by different types of mosquitoes or by braking. These insects are therefore also referred to as disease carriers (vector). In general, travelers to tropical countries should familiarize themselves with the typical diseases and infections in their respective travel destination before traveling.

It is useful to know the respective vector because the insects are active at different times of the day. The knowledge of the different activity times of the insects helps to prevent stings.

	Disease transmitter (vector)
Lymphatic filarioses	Mosquitoes of the species Aedes (partially diurnal), Anopheles, Cule, Mansonia (all predominantly nocturnal)
Subcutaneous filarioses	Chrysops brakes, blackflies (only diurnal)
Serous filarioses	Culicoides mosquitoes (especially active in the morning and evening hours)

Filariasis: examinations and diagnosis

After a tropical journey you should always point out the doctor on the journey back in case of complaints. An indication of a filariasis often brings the exact survey of the patient, taking into account the past holiday or whereabouts.

In the early phase of filariasis, the number of certain types of white blood cells (eosinophilic granulocytes) typically increases in the blood. These granulocytes are cells of the immune system and involved in the defense reaction. However, this increased number of eosinophilic granulocytes is not specific for filariasis, but may also be conspicuous in other parasitic diseases or allergic disorders in the blood.

The doctor then determines the filariasis by microscopically detecting the microfilariae in the blood. Depending on which mosquitoes have probably transmitted the pathogen, the blood should be taken at different times: The microfilariae have namely adapted to the pricking habits of the mosquito species. Many sting mainly at night, which is why the microfilaria almost exclusively in these hours in the blood. In Loa Loa, the microfilariae are most common at lunchtime, with lymphatic filariasis rather at night. In onchocerciasis, microfilariae do not enter the blood at all and the worm can only be detected directly under the skin.

If the search for microfilariae yields a negative result, the doctor uses specific tests to find specific antibodies in the blood. If the worm under the skin is observed during its migration, this can also be diagnosed. If internal organs are already affected, other imaging techniques (such as computed tomography, magnetic resonance imaging) are available to detect the damage already suffered.

Filariasis: treatment

In the treatment of different filarioses are different anthelmintics used. These are drugs that are effective against worm infections, the following drugs are:

• Diethylcarbamazine (DEC)
• Ivermectin
• suramin
• mebendazole

Basically, the filaria are killed by these drugs very effective. More problematic is to recognize the disease at all, so that the appropriate treatment measures can be initiated.

Recently, the antibiotic doxycycline is also used in lymphatic filariasis and onchocerciasis. It kills bacteria, which the filaria need for their reproduction. When these symbiotic bacteria are killed, the worms can not reproduce.

In some Filariosen dying of the worms triggers a strong immune reaction in the body, so that additional cortisone must be given. This anti-inflammatory, immunodeficiency drug prevents a possible overshooting immune response that can otherwise trigger an allergic (anaphylactic) shock.

A special treatment measure is used in elephantiasis: Since the worms in the lymphatic filarioses live in the lymphatic vessels and destroy them, there is a congestion of lymphatic fluid in the tissue. Therapeutically, one can try to eliminate this lymph congestion with regular manual lymphatic drainage and the permanent wearing of compression stockings.

Filariasis: surgery

In the case of a very pronounced clinical picture, as is the case with elephantiasis (lymphatic filariasis), surgery is sometimes necessary to somewhat reduce the enormous accumulations of fluid in the testes, breasts or legs. In these plastic surgeries, excess tissue is removed. A complete reconstruction of the destroyed tissue is not possible, so that can not be spoken of a cure in the strict sense.

In onchocerciasis, the worms under the skin can be removed by surgery. In Loa-Loa disease, the worm can be cut from the conjunctiva of the eye when discovered there.

Filariasis: disease course and prognosis

The prognosis of filariasis depends on how large the number of pathogens is and how long the affected person stays in the tropical areas. During the filariasis, the immune system is weakened and the body is more susceptible to further diseases. Especially in the tropics, further infections can lead to life-threatening complications.

The adult (adult) worms can survive in the host for several years. It may take several months to years for microfilariae to appear in the blood so that infection will be noticed late or not at all. The sooner the right treatment, the better the prognosis.

In lymphatic filariasis, the development of disfiguring lymphoedema (elephantiasis) can be avoided by consistent therapy.

For Loa Loa the prognosis is generally good. The disease is usually recognized due to the typical “Calabar bump”. In case of an attack of the larynx, however, the airways can be narrowed. Such swelling can be life threatening. In addition, in rare cases Loa Loa can cause brain inflammation (encephalitis), which can be fatal or at least cause serious neurological sequelae. Since the worm can survive for a decade and a half under human skin and produce microfilaria, consistent treatment of all affected people is essential if possible to stem the disease.

Onchocerciasis is the most threatening filariasis for the local population due to the often severe damage to the eyes and skin. However, with timely treatment, the prognosis is much better.

The serous filarioses are classified as relatively harmless in terms of disease severity and possible complications.

Prevent filarioses

Because all filariases are transmitted through insect bites, the most effective method of preventing them is to generally avoid insect bites. Travelers should be aware of any illness and infection before traveling to tropical countries.

Follow these measures to avoid insect bites in tropical countries:

• Wear long, light clothes
• Keep in mind that Aedesmücken and brakes are also diurnal
• Use mosquito pellets. Make sure the products are trophy-proven and recommended by organizations like the WHO.
• Note that repellents only work locally on the area of ​​the skin where they are applied.
• Use a mosquito net to sleep. Recommended are repellents impregnated mosquito nets.
• Avoid riverbeds or wetlands as insects are particularly likely.
• For longer stays: Seal windows with mosquito nets.
• A few weeks before departure, talk to a tropical medicine / travel doctor about possible medication to protect against infection and necessary travel vaccinations. Prevention can be given
• If you perform malaria prophylaxis with doxycycline while traveling, it is likely to be lymphatic as well filariasis and onchocerciasis effectively.