Introduction

Filarial infections are parasitic infections caused by different types of filarial worms also known as nematodes. These are organisms, which depend on the host they infect for their survival and cause them harm at the same time. Acanthocheilonemiasis is an example of a filarial infection caused by the parasite Acanthocheilonema perstans. Other examples of filarial infections include lymphatic filariasis, onchocerciasis, and loiasis, all of which are caused by different species of filarial worms.

Common filarial infections

Lymphatic filariasis 

Lymphatic filariasis, also known as elephantiasis, may be caused by three different filarial worms. Most commonly, it is caused by Wuchereria bancrofti, Brugia malayi, and Brugia timori. These nematodes tend to settle within the lymphatic system. By doing so, they cause blockage in lymph tissues, which in turn leads to the build-up of fluid in the body tissues. 

Symptoms and complications 

Considering the nature of the infection, the most common symptoms include: 

• Fluid build up in the lymph tissues
• Fluid build up in other body tissues leading to a swelling commonly known as oedema
• A condition called hydrocele that involves swelling of the scrotum due to fluid buildup 

Some people may develop further conditions and so symptoms such as:

• Filariatic fever, which is characterised by flu-like symptoms may cause a headache, fever, or chills
• Filarial abscess, which occurs when the swelling in a certain place within the body breaks open, releasing dead adult nematodes and may possibly cause presentation of bumps in the subcutaneous tissues 
• Tropical pulmonary eosinophilia involves the lungs and is caused by the body’s immune response to the infection. It may present with symptoms like wheezing or being short of breath^1,2 

Onchocerciasis 

Onchocerciasis is caused by the organism Onchocerca volvulus. The disease is also known as African river blindness based on where it is most common, where its vector (another organism that transmits them to humans) lives, and the symptoms it causes. Interestingly, the symptoms do not occur by physical action from the nematode but rather due to the immune response to the dead worms.

Symptoms and complications

Usually, the parasite will affect the skin first causing itching, red bumps on the skin, hard patches of skin, as well as skin discolouration that is sometimes referred to as ‘leopard skin’. Next, ocular symptoms tend to occur beginning with sensitivity to light, conjunctivitis (pink eye), corneal damage, and a gradual loss of vision that may end with complete blindness.³

Loiasis 

Loiasis, otherwise known as African eye worm, is caused by the nematode Loa loa. This parasite can live in multiple areas of the body including the blood, skin, lungs, and lymph tissue, and may also enter the eye. Hence, the symptoms of the disease affect multiple body areas.

Symptoms and complications

Due to its ability to live in the skin, the nematode may cause symptoms of itching, swelling, and seeing worms crawling under the skin. As they may enter the eyes, people are also able to see the worms crawling along their eyes, hence the name ‘eye worm’. Otherwise, the parasite may also cause fatigue as well as muscle and joint pains.^4,5 

Epidemiology

Geographic distribution of Acanthocheilonemiasis 

Acanthocheilonemiasis caused by Acanthocheilonema perstans is most commonly found to occur in Africa but may also occur in South America. Likewise, onchocerciasis and loiasis are also usually found to occur in Africa. Filariasis however, does not mainly occur in Africa but also in a variety of tropical places in Asia, South America, the Caribbean, and the Western Pacific.^2,3,4,6 

Transmission vectors

Although each parasite is transmitted by a fly or mosquito type vector, the species of fly or mosquito tend to differ as well as the amount of possible vectors. For acanthocheilonemiasis, there is one fly species that is able to act as a vector, which is the fly species called Culicoides, more simply referred to as a midge. For filariasis, the vectors are mosquitoes and there are five possible transmitting species including the Aedes, Anopheles, Culex, Mansonia, and Ochlerotatus. For onchocerciasis the vector is the simulian black fly and for loiasis it is the deerfly.^2,3,5,6 

Clinical manifestations

Symptoms of Acanthocheilonemiasis 

For acanthocheilonemiasis, symptoms tend to involve the skin as it is a disease which primarily affects subcutaneous tissues. The skin-affecting symptoms include:

• Itching
• Nodules found underneath the skin tend to be firm and painful. These nodules are also able to be moved around
• Swelling 

There are also symptoms that are less skin-specific including a fever, fatigue, and enlarged lymph nodes.⁷

Comparison with symptoms of other filarial infections 

Similarities 

Compared to filariasis, acanthocheilonemiasis also causes swelling as well as certain flu-like symptoms like fever and fatigue. Onchocerciasis and acanthocheilonemiasis both present with itching as does loiasis, which similarly to acanthocheilonemiasis also may present with swelling and fatigue.

Differences

The three diseases have quite distinct symptoms from each other and so should not be too hard to tell apart. The most characteristic symptom of acanthocheilonemiasis is the subcutaneous nodules, which none of the other filarial infections present with. Furthermore, ocular involvement may only be pinned to onchocerciasis and loiasis but for loiasis, it will usually only be seeing the worm crawling so if any other eye symptoms occur it is reasonable to assume the infection to be onchocerciasis. 

Diagnosis

Diagnostic methods for Acanthocheilonemiasis 

The most common way of diagnosing acanthocheilonemiasis is through a blood smear. For the blood smear, a sample of your blood will be taken via either a finger prick or blood draw. The blood sample will then be examined using a microscope to check for the presence of microfilariae (parasitic offspring). 

Comparison with other filarial infection diagnosis

The aforementioned method is also used for the diagnosis of filariasis and loiasis. This is a slight issue because these are all filarial worms, they have a similar thread-like structure. This makes the consideration of presented symptoms even more important. Polymerase chain reactions are also available for diagnosis but they are rarely used in clinics. For loiasis, a doctor may also make a diagnosis by seeing the worm in a patient's eye. For onchocerciasis, a doctor is more likely to take a skin sample without any blood and observe it under a microscope. Although also a filarial worm, Onchocerca volvulus may be distinguished from other filarial infection-causing nematodes as it has a slightly different structure meaning, it has no sheath or nuclei in the tail. There are also serological tests which may be used to detect antibodies of Onchocerca volvulus, implying infection. 

Treatment and management

Treatment options for Acanthocheilonemiasis 

If mild, acanthocheilonemiasis tends to be self-limiting and may not require any medication. If medication is administered, it would usually be an antifilarial drug like, ivermectin or diethyl-carbamizine (DEC). If the adult worms are big enough, a patient may require surgery for their removal. 

Comparison with treatment of other filarial infections 

A similar approach is used for filariasis along with surgery to minimise the swelling by aiding drainage. Onchocerciasis and loiasis are more problematic to treat. For onchocerciasis, treatment with DEC causes serious side effects and ivermectin does not kill the adult worms, only the microfilariae and so it does not fully remove the disease. For loiasis, antifilarial medications can cause life-threatening effects if the number of microfilariae in the blood is above 8,000 per millilitre. In those cases, the patient may be recommended to undergo a blood filtering procedure or be given albendazole (antihelminthic medication) to decrease blood microfilariae to safer levels. 

Prevention and control

Considering all the mentioned infections are transmitted by insect vectors (flies/mosquitoes), action taken to prevent bites is necessary. These would include wearing long-sleeved trousers and tops to reduce the amount of skin exposed to potential bites. Bug repellent spray effective against the specific vector should also be considered to keep the different types of flies/mosquitoes away. When sleeping, it is recommended to use a mosquito net to prevent contracting filariasis. In some cases, people travelling to areas with a higher chance of infection, like Africa, may be advised to take DEC prophylactically (before becoming infected).^1,2,3,4,5,6

Summary 

Acanthocheilonemiasis is a filarial infection caused by a parasite classified as a filarial worm. It bears some similarity to other infections caused by different filarial worms like filariasis, onchocerciasis, and loiasis. Fortunately, there are symptoms, which allow differentiation between the different diseases like the types of rashes developed or the organs affected giving distinct organ-specific symptoms. The diagnostic process is similar for the diseases and involves a blood smear, with only onchocerciasis being the outlier where a skin snip is used instead. The medication used for treatment tends to be DEC or ivermectin for all the mentioned infections, but the outcome and side effects differ so certain factors, like the amount of microfilariae in the blood, must be considered before administration. As they are all caused by either fly or mosquito vectors, prevention to avoid bites will be the same including bug spray and covering oneself up as much as possible with clothing.