Introduction

Filariasis infections (fil-uh-RIGH-uh-siss) are diseases caused by parasitic worms, which can spread via the bite of blood-feeding mosquitoes contaminated with worm larvae.¹ These parasites affect 120 million people in 72 countries worldwide, particularly in the warm subtropical climates of Asia, Africa, South America, and the Caribbean, and can lead to elephantiasis, a disorder characterised by significant swelling of the limbs and genitalia if left untreated.²

With over 885 million people estimated to be at risk of infection³, this disorder remains “scientifically silent”. This means that despite these alarming statistics and the associated increase in morbidity, filariasis infections are often overshadowed by other diseases, leading to a lack of support from global funding agencies.⁴ 

Types of filariasis 

There are three main types of filariasis based on the worms and where they reside in the body:

1. Lymphatic filariasis: This affects the lymphatic system, an important network of vessels and glands that drains excess fluids from body tissues and transports them back to the bloodstream.⁵ It ranks second globally in causing lasting deformity and impairment, after leprosy⁶
2. Subcutaneous filariasis: Unlike lymphatic filariasis, this type affects the subcutaneous tissues (the layer of fat directly beneath the skin). The most common filarial worm for this type is Loa loa (the African eye worm), which can also result in loiasis 
3. Serous cavity filariasis: These worms reside in the body’s cavities, specifically the space around the abdomen^2,6 

What happens to the body if you get infected? 

There are three common worm species (also known as filariae) that frequently cause the disease:

• Wuchereria bancrofti
• Brugia timori
• Brugia malayi 

These worms can invade various parts of the body, leading to short-term (acute) or long-term (chronic) conditions. Infection can occur at any age; however, symptoms in children typically do not appear until adolescence. 

Filariasis worms produce millions of microfilariae, or immature larvae, which enter the bloodstream. These are picked up by mosquitoes when they feed on the blood of an infected person. 

Once ingested, the microfilariae move to the thoracic muscles of the mosquito, where they mature into first-stage larvae (L1) and later into infectious third-stage larvae (L3) under optimal temperatures and conditions. The L3 larvae are then transmitted to another human host when the mosquito bites again.⁷ 

Over the course of several months, the larvae travel to the subcutaneous tissues or lymphatic system, where they mature into adult worms. The transmission cycle continues when adult female and male worms mate and produce microfilariae, which migrate to the bloodstream and are then ingested by mosquitos. 

It is worth noting that adult worms can survive for several years, sometimes as long as 15 years or more. The likelihood of serious symptoms increases with the length of time these worms live undetected in the body.

Although neurological involvement in filariasis is relatively uncommon, it can occur when L3 larvae infiltrate neural tissues instead of other areas of the body. Once in the bloodstream, the larvae have the ability to cross the blood-brain barrier (think of this as the brain’s most important shield against bacteria and viruses) and enter the peripheral nerves.⁸ 

The peripheral nerves are responsible for delivering important messages from the brain to the rest of the body and back.⁹

Scientists are investigating the exact mechanism by which filariasis worms are able to penetrate the brain’s tissues. Nevertheless, it is theorised that a breach of the blood-brain barrier may lead to inflammation of the surrounding tissues (in other words, swelling), which could result in the development of other infections and illnesses.⁸ 

General symptoms

Most people do not experience any symptoms in the early stages of infection; however, microfilaria can still be detected in blood smears. Unfortunately, those who do experience symptoms typically suffer from one or more within the first few months:² 

• Fever 
• Skin lesions
• Headache

As mentioned previously, the common chronic condition that develops if left untreated is elephantiasis. Over time, patients have reported:² 

• Body aches
• Swollen lymph nodes
• Nausea
• Edema
• Kidney damage
• Genital diseases

Neurological manifestations

Although infections of the nervous system are incredibly rare, there have been case studies of individuals developing secondary infections due to a high volume of adult worms, the length of time the worms reside in the body, or the level of exposure to the disease.⁸ Some reported conditions include:² 

• Encephalitis: Inflammation of the brain 
• Meningitis: Inflammation of the lining of the brain and spinal cord 
• Myelopathy: A condition that results in spinal compression

Diagnostic of filariasis

Depending on the severity of the disease, you may undergo the following:² 

• Imaging techniques: Your doctor may order a magnetic resonance imaging (MRI) scan or a CT scan to assess the presence of worms and visualise any inflammation or structural changes in the body and brain. For males, ultrasonography may be recommended
• Alere filariasis test strip: A quick diagnostic tool used to identify Wuchereria bancrofti in blood samples obtained through finger pricking.¹⁰ This is collected at specific times of the day due to the periodicity of the microfilariae. Diethylcarbamazine citrate (DEC) may be given to stimulate the bacteria
• Polymerase chain reaction (PCR): This can be used to detect the DNA of microfilariae 
• Cerebrospinal fluid (CSF) analysis: This measures the fluid that surrounds the spinal cord and brain (cerebrospinal fluid)¹¹

Treatment for filariasis

This depends on the type of infecting parasite, as well as the duration and severity of the symptoms. Treatment primarily involves the use of antiparasitic medications, such as DEC which can be used to eliminate filarial worms (with the exception of Loa loa worms, as this can worsen the progression of eye disease).⁶ Other treatments options include:⁶

• Antiparasitic drugs: The most effective treatment to reduce the number of worms is by killing them or stopping their reproduction. Some examples include albendazole, DEC, ivermectin, mebendazole, and praziquantel
  • Side effects of these drugs may be managed by taking anti-inflammatory medications
• Surgery: In serious cases, surgery may be necessary to remove the remains of adult worms and any plaques that have formed around them
• Elephantiasis control: Techniques to manage edema include compression clothing or elevation of the limbs
• Preventive Chemotherapy: In populated areas with a high risk of infection, the administration of combined drugs can help reduce the risk of transmission¹²

Prevention 

Avoiding bug bites is the best defense against filarial infestations. You can reduce your risk of getting bitten by mosquitoes by:⁶

• Wearing long-sleeved clothing
• Applying insect repellent to exposed areas of your skin
• Sleeping under mosquito nets
• Ensuring that you regularly wash with soap and water

FAQs

Is filariasis contagious? 

No. Filariasis is transmitted through mosquito bites. 

Is there any cure?

No. You can receive treatment with antiparasitic drugs to reduce the number of worms and relieve your symptoms. In the worst case scenario, surgery may be required to remove dead adult worms in cases of serious infection or as advised by your healthcare provider. At the moment there are no vaccines or permanent cures, but experts are working on developing one.

How likely are you to get filariasis? 

If you are planning on travelling abroad to South America, Africa, or Asia, it is very unlikely that you will get filariasis from a quick trip to one of these locations. However, If you are looking to spend months or years living in a high-risk location, your chances of contracting the illness increase. Always follow the appropriate prevention methods, and if you develop any of the symptoms described, please seek the advice of a healthcare professional for diagnostic tests. 

When should you consult a doctor/healthcare professional?

If you notice any unexplained swelling or thickening of your skin, particularly in your:

• Arms
• Legs
• Breasts
• Scrotum
• Vulva

It’s essential to consult a medical professional promptly for an early diagnosis. They can conduct appropriate tests to accurately diagnose the issue, provide reassurance, and assist you to the best of their best abilities.

Summary

Filariasis is a parasitic disease spread by mosquito bites, affecting 120 million people worldwide, primarily in subtropical regions. It can cause severe symptoms like elephantiasis and chronic swelling if untreated. The disease is categorized into three types: lymphatic, subcutaneous, and serous cavity filariasis, with worms capable of living undetected for over a decade.

Diagnosis includes blood tests and imaging, while treatment involves antiparasitic medications or surgery in severe cases. Prevention focuses on avoiding mosquito bites and administering preventive drugs in high-risk areas. Early detection and proper care are essential to managing this often overlooked but impactful disease.