Filariasis

Definition¹

Filariasis is a condition caused by chronic infection with parasitic worms. This chronic infection is characterised by swelling of the extremities, hydroceles, and testicular masses.

Contraction¹

The original infection is caused by mosquito bites, which act as a vector carrying the larvae of the nematodes, which are inserted into the bloodstream as the mosquito feeds. The larvae collect in lymph nodes continuing their life cycle: growth, sexual reproduction, repeat until death. Worms populate throughout the lymph nodes, and with the growth of the worms and the number of worms, they occlude the lymph nodes and lymphatic systems, preventing actions such as lymphatic draining, depleting the body's resistance to disease and infection, primarily streptococcal (Strep A) and fungal infections.

Chronic infection leads to inflammation and remodelling of lymph nodes. These changes result in symptoms such as swelling of the extremities, similar to elephantiasis.

Female nematodes involved in this parasitic infection can sexually produce for up to 5 years, and worms can live up to 9. The females produce microfilariae, which are deposited into the circulatory system.

3 types of nematode worms can cause filariasis, and 5 types of mosquitoes can carry the parasite.

Prevalence¹

Over 120 million people from subtropical climates such as South America, Africa, Southern Asia, the Western Pacific, and the Caribbean are infected. Filariasis is the 2nd largest saboteur for permanent deformity.

In these regions, 20% of infected individuals are children⁵, with about half of filariasis patients being in their 30s and 40s. 

Diagnosis¹

Diagnosis of infection can be through several methods:

• Peripheral Smear: Prepared thick and thin blood smears with certain chemicals and steps that can detect if microfilariae are present within the blood samples, indicative infection. The most common detection method is advised by the CDC
• PCR: The detection of latent disease through the parasite antigens method is preferred. (not approved by the FDA)
• Scrotal Ultrasound: In males, you can detect movement of adult worms, even in asymptomatic cases, adult worms residing in lymphatic vessels

Filariasis is diagnosed later on after the infection. Diagnostic factors follow the observation of the symptoms listed above. Due to the chronic nature and the large changes in dermal layers, they may test for infection.

Symptoms^{1, 2, 3}

• Increased bacterial and fungal infections: Lymph node occlusion leads to increased infection
• Hydrocele: Fluid filling the testicular sac. It is the most common symptom among males
• Increased fever: Headaches, chills, and general malaise. Most often occurs with occlusion of lymph nodes and channels
• Acute filariasis, episodic occurrences of:
  • Lymphadenitis – inflammation of the lymph glands
  • Lymphangitis – inflammation of the lymph channels
  • Lymphedema – subsequent swelling of the limbs, breasts, or scrotum. Follows repeated bouts of lymphangitis.
• Acute dermatolymphangioadenitis attacks (ADLA): A sudden fever with lymphadenopathy, caused by repeated bouts of lymphangitis
• Tropical pulmonary eosinophilia (TPE): A rare extreme reaction that results in asthma-like symptoms and restrictive lung capacity

Adult worms can cause inflammation and widening of lymph channels, causing difficulty for lymph products to enter the bloodstream and lymph drainage, reducing immunity and causing lymphedema.

Reason for difference

So why is there a difference between patients dependent on age?

Instances of infection and progression

In these countries, filariasis is a common danger, and most patients are infected during childhood.³ The maximum infection rate is within 16-20 years of age,⁴ with an asymptomatic period while the worms develop.³

Due to the nature of the infection, there is a progression of symptoms, manifesting after years of infection and getting worse without treatment. The longer the infection, the worse the symptoms. This is because it is a progressive condition in line with parasitic sexual reproduction and growth, hence the large number of filariasis patients in their 30s and 40s.^{1, 2, 3}

Immunity⁴

As one gets older, the immune system slowly improves the surroundings. Children’s immunity to the infection is limited due to the type of immune cells they present.

As people age there is increased immunity against the infection, decreasing the likelihood of contracting the disease. Strengthening immunities as a person ages, and an increasing number of particular antibodies that help fight off the infection.

The quality of the immune response in infected individuals is the differentiating factor between symptomatic and asymptomatic patients, with a better response equalling a longer asymptomatic period.

Child/Paediatric

Signs and symptoms

Chronic symptoms of infection and filariasis may appear in some, depending on the incubation time and immune system quality against the parasite.  

At this stage, there are worms within the lymphatic system and bloodstream, with microfilariae circulating the body, but with limited signs of infection. Symptoms often start presenting themselves after puberty.¹

Commonly, children around this age who do present symptoms complain about pains in the scrotal area, which can be enlarged due to acute filariasis. They often leave many public spaces due to public stigmatisation but are not yet disabled or hugely deformed.⁵

Infection rate

The point of infection in children has ranged from 3-15 years of age, earlier infection has occurred in some children with  filariasis before 18 years.^{3, 5}

Adult

Signs and symptoms

At this period, an individual is rarely asymptomatic. Without any form of prevention, chronic symptoms set in and are often disabling. They present all the listed symptoms, and the longer the disease goes untreated, the worse the symptoms are.

New symptoms may appear, such as:

• Filarial Abscesses: Pus-filled localised nodule growth. These abscesses are painful and grow until they rupture, releasing fluid and dead adult worms. Granulomatous reactions can lead to lumps subcutaneously^{1, 2}
• Elephantiasis – Extreme growth of limbs, causing disability^{1, 3}

Infection rate

Infection at this age is much rarer due to increased immunity and improved immune response.⁴ As you get older, the chances of infection decline, but due to the asymptomatic period, it is difficult to tell the exact point of infection without regular testing.

Differences in care

Prevention

Most often, points of infection are people outside, traveling to and from school/work, socialising, or doing chores. Without a mosquito net surrounding them, there will always be risks in not addressing their educational, professional and social needs.

Methods can be taken to reduce the risk of being bitten without impeding children’s access to institutions and their needs.⁶

• Mosquito-killing methods, like electrical bug zappers, can be used to attract the mosquitos away from individuals and reduce their numbers
• Mosquito repellents and chemicals can be used to prevent mosquitos and reduce bites
• Long-sleeved clothing means there is less skin to target, although may not be as accessible in the subtropical climates where this disease resides
• Avoid peak mosquito hours when they are most active
• Limit access to enclosed spaces and standing water nearby to reduce attraction

These methods are not certain but reduce the risk of infection from any mosquito- borne disease. These preventative measures are not available to all but should be made accessible if we ever hope to reduce illness caused by these parasites.

Current therapies^1,2,3

Medicinal

Diethylcarbamazine (DEC) is the most used form of therapy, usually taken by itself, and individuals who spot infection early respond well to treatment.

• A single combined dose of ivermectin, albendazole, and DEC removes 96% of microfilariae up to 3 years of infection

DEC is not used where Loa Loa disease is prominent, as it can cause eye disease progression and encephalopathy.

• In these areas, doxycycline is used instead, slowing inflammatory and swelling symptoms characteristic of lymphedema.

Surgical

Surgical interventions occur later in the disease progression to remove some excess skin created through swelling. Flavonoids and coumarin applied topically to the site of swelling are thought to increase macrophage activity and decrease swelling caused by lymphedema.

Surgery is also used to increase the drainage capabilities of the lymphatic system by creating new exit points.

Management

Assisting patients with methods of comfort such as comfortable footwear, regular hygiene, and washing, especially in the extremities prone to fungal infection, along with the use of anti-bacterial/fungal cream to prevent infection on a weak immune system and prevent lymphangitis.

 Compressive bandages, pneumatic compression, limb elevation, and cold/heat therapies help prevent the quick onset of lymphedema.

New therapies

While a vaccine is not yet available, the studies and the identification are ongoing endeavours.

Treatment for a non-filarial disease successfully used a carbon monoxide laser to induce heat damage to excess swelled skin, causing tightening and remodelling of skin tissue, reducing the excess swelling in that region. This was effective on both skin lesions and lymphocutaneous fistulas, is said to be a treatment for chronic filariasis perhaps but has not yet been concluded whether it is viable. 

Conclusion

Filariasis, a mosquito-carried disease, is the 2^nd most common permanent deformity-causing disease, causing elephantiasis in the extremities. This arises from swelling of the extremities and testes through poor lymphatic drainage, occlusion, and circulating microfilariae causing inflammation, swelling, fever, and chronic lymphedema.

While most are infected as children, they often don’t present any symptoms until after puberty, and it doesn’t become chronic or deformative for a few years. This is due to differences in incubation time and quality of the immune response.

There are current prevention methods and medicinal interventions; however, if the disease has progressed too far, the only thing to do is to manage the symptoms. Research on a vaccine is underway,  but no drug trials have commenced.