Secondary bacterial infection is common among patients with filariasis. Compromised immune function due to lymphatic damage in addition to lymph node ulcerations and abscesses exposure and impaired circulation due to elephantiasis can cause secondary bacterial or fungal infection. Elephantiasis, in addition to the physical burden of a swollen limb, can be a severely dehabilitating condition given bacterial infection. Part of the WHO's "Strategy to Eliminate Lymphatic Filariasis" targets hygiene promotion programs in order to alleviate the suffering of affected individuals (see Prevention Strategies).

However, clinical manifestations of infection are variable and depend on several factors, including host immune system, infectious dose, and parasite strain differences. Most infections appear asymptomatic, yet vary from individual to individual. Individuals living in endemic areas with microfilaremia may never present with overt symptoms, whereas in other cases, only a few worms can exacerbate a severe inflammatory response.

The development of the disease in humans, however, is not well understood. Adults typically develop worse symptoms, given the long exposure time required for infection. Infection may occur during childhood, but the disease appears to take many years to manifest. The incubation period for infection ranges from 1 month to 2 years and typically microfilariae appear before overt symptoms. Lymphedema can develop within six months and development of elephantiasis has been reported within a year of infection among refugees, who are more immunologically naive. Men tend to develop worse symptoms than women.

Secondary bacterial infection is often observed with lymphatic filariasis. Rigorous hygiene practices, including washing with soap and water daily and disinfecting wounds can help heal infected surfaces, and slow and potentially reverse existing tissue damage. Promoting hygiene is essential for lymphatic filariasis patients given the compromised immune and damaged lymphatic systems and can help prevent suffering and disability.

The World Health Organization recommends mass deworming—treating entire groups of people who are at risk with a single annual dose of two medicines, namely albendazole in combination with either ivermectin or diethylcarbamazine citrate. With consistent treatment, since the disease needs a human host, the reduction of microfilariae means the disease will not be transmitted, the adult worms will die out, and the cycle will be broken. In sub-Saharan Africa, albendazole (donated by GlaxoSmithKline) is being used with ivermectin (donated by Merck & Co.) to treat the disease, whereas elsewhere in the world, albendazole is used with diethylcarbamazine. Transmission of the infection can be broken when a single dose of these combined oral medicines is consistently maintained annually for a duration of four to six years. Using a combination of treatments better reduces the number of microfilariae in blood. Avoiding mosquito bites, such as by using insecticide-treated mosquito bed nets, also reduces the transmission of lymphatic filariasis.

The Carter Center's International Task Force for Disease Eradication declared lymphatic filariasis one of six potentially eradicable diseases. According to medical experts, the worldwide effort to eliminate lymphatic filariasis is on track to potentially succeed by 2020.

For similar-looking but causally unrelated podoconiosis, international awareness of the disease will have to increase before elimination is possible. In 2011, podoconiosis was added to the World Health Organization's Neglected Tropical Diseases list, which was an important milestone in raising global awareness of the condition.

The efforts of the Global Programme to Eliminate LF are estimated to have prevented 6.6 million new filariasis cases from developing in children between 2000 and 2007, and to have stopped the progression of the disease in another 9.5 million people who had already contracted it. Dr. Mwele Malecela, who chairs the programme, said: "We are on track to accomplish our goal of elimination by 2020." In 2010, the WHO published a detailed progress report on the elimination campaign in which they assert that of the 81 countries with endemic LF, 53 have implemented mass drug administration, and 37 have completed five or more rounds in some areas, though urban areas remain problematic.

Prevention focuses on protecting against mosquito bites in endemic regions. Insect repellents and mosquito nets are useful to protect against mosquito bites. Public education efforts must also be made within the endemic areas of the world to successfully lower the prevalence of "W. bancrofti" infections.

Filariasis can also affect domesticated animals, such as cattle, sheep, and dogs.

Elephantiasis caused by lymphatic filariasis is one of the most common causes of disability in the world. A 2012 report noted that lymphatic filariasis affected 120 million people and one billion people at risk for infection. About 40 million people were disfigured or incapacitated by the disease in 2015. It is considered endemic in tropical and subtropical regions of Africa, Asia, Central and South America, and Pacific Island nations.

In areas endemic for podoconiosis, prevalence can be 5% or higher. In communities where lymphatic filariasis is endemic, as many as 10% of women can be afflicted with swollen limbs, and 50% of men can suffer from mutilating genital symptoms.

Filariasis is considered endemic in 73 countries; 37 of these are in Africa.

- In the Americas, it is present in Brazil, Costa Rica, the Dominican Republic, Guyana, Haiti, Suriname, and Trinidad and Tobago.

- In Asia, it is present in Bangladesh, Cambodia, India, Indonesia, Laos, Malaysia, Maldives, the Philippines, Sri Lanka, Thailand, Timor-Leste, and Vietnam.

- In the Middle East, it is present only in Yemen.

- In the Pacific region, it is endemic in American Samoa, the Cook Islands, Fiji, French Polynesia, Micronesia, Niue, Papua New Guinea, Samoa, Tonga, Tuvalu, and Vanuatu.

In many of these countries, considerable progress has been made towards elimination of filariasis. In July 2017, the World Health Organization (WHO) announced that the disease had been eliminated in Tonga. Elimination of the disease has also occurred in Cambodia, China, the Cook Islands, Niue, the Marshall Islands, South Korea, and Vanuatu, according to the WHO.

Brugia timori is a human filarial parasitic nematode (roundworm) which causes the disease "Timor filariasis." While this disease was first described in 1965, the identity of "Brugia timori" as the causative agent was not known until 1977. In that same year, "Anopheles barbirostris" was shown to be its primary vector. There is no known animal reservoir host.

The WHO is coordinating an effort to eradicate filariasis. The mainstay of this programme is the mass use of antifilarial drugs on a regular basis for at least five years.

In April 2011, Sri Lanka was certified by the WHO as having eradicated this disease.

Filarial diseases in humans offer prospects for elimination by means of vermicidal treatment. If the human link in the chain of infection can be broken, then notionally the disease could be wiped out in a season. In practice it is not quite so simple, and there are complications in that multiple species overlap in certain regions and double infections are common. This creates difficulties for routine mass treatment because people with onchocerciasis in particular react badly to treatment for lymphatic filariasis.

Anthelmintics such as diethylcarbamazine and albendazole have shown promise in the treatment of "Brugia timori" filariasis. Some researchers are confident that "Brugia timori" filariasis may be an eradicable disease. Related filarial nematodes have been found highly sensitive to elimination of their endosymbiotic Wolbachia bacteria, and this may be a powerful attack route against "Brugia timori" as well.

Tropical (pulmonary) eosinophilia, or TPE, is characterized by coughing, asthmatic attacks, and an enlarged spleen, and is caused by "Wuchereria bancrofti", a filarial infection. It occurs most frequently in India and Southeast Asia. Tropical eosinophilia is considered a manifestation of a species of microfilaria. This disease can be confused with tuberculosis, asthma, or coughs related to roundworms.

Tropical pulmonary eosinophilia is a rare, but well recognised, syndrome characterised by pulmonary interstitial infiltrates and marked peripheral eosinophilia. This condition is more widely recognised and promptly diagnosed in filariasis-endemic regions, such as the Indian subcontinent, Africa, Asia and South America. In nonendemic countries, patients are commonly thought to have bronchial asthma. Chronic symptoms may delay the diagnosis by up to five years. Early recognition and treatment with the antifilarial drug, diethylcarbamazine, is important, as delay before treatment may lead to progressive interstitial fibrosis and irreversible impairment.

The condition of marked eosinophilia with pulmonary involvement was first termed tropical pulmonary eosinophilia in 1950. The syndrome is caused by a distinct hypersensitive immunological reaction to microfilariae of" W. bancrofti" and "Brugia malayi". However, only a small percentage (< 0.5%) of the 130 million people globally who are infected with filariasis apparently develop this reaction. The clearance of rapidly opsonised microfilariae from the bloodstream results in a hypersensitive immunological process and abnormal recruitment of eosinophils, as reflected by extremely high IgE levels of over 1000 kU/L. The typical patient is a young adult man from the Indian subcontinent.

A persistent or recurrent cough that gets aggravated at night, weakness, weight loss and a low fever raises the possible diagnosis of this disease. Some children with this disease may also have enlarged lymph nodes in the neck and elsewhere. Others may cough up a little blood and may also have a wheeze.

A hydrocele can be produced in four ways:

- by excessive production of fluid within the sac, e.g. secondary hydrocele

- through defective absorption of fluid

- by interference with lymphatic drainage of scrotal structures as in case of elephantiasis

- by connection with a hernia of the peritoneal cavity in the congenital variety, which presents as hydrocele of the cord

Secondary hydroceles due to testicular diseases can be the result of cancer, trauma (such as a hernia), or orchitis (inflammation of testis), and can also occur in infants undergoing peritoneal dialysis. A hydrocele is not a cancer but it should be excluded clinically if a presence of a testicular tumor is suspected, however, there are no publications in the world literature that report a hydrocele in association with testicular cancer. Secondary hydrocele is most frequently associated with acute or chronic epididymo-orchitis. It is also seen with torsion of the testis and with some testicular tumors. A secondary hydrocele is usually lax and of moderate size: the underlying testis is palpable. A secondary hydrocele subsides when the primary lesion resolves.

- Acute/chronic epididymo-orchitis

- Torsion of testis

- Testicular tumor

- Hematocele

- Filarial hydrocele

- Post herniorrhaphy

- Hydrocele of an hernial sac