Filariasis of uncommon nature in India.

Lymphatic filariasis (LF) is caused by nematodes that inhabit the lymphatics and subcutaneous tissues. Three species, which are responsible for most of the morbidity due to broad spectrum of filariasis in humans are Wuchereria bancrofti, Brugia malayi, and Brugia timori. Dirofilaria spp. cause accidental infections in humans. These parasites are transmitted by different species of mosquitoes belonging to the genera Culex, Anopheles, Aedes, and Mansonia in different regions of the tropics, although more than 50% of the LF infections all over the world are transmitted by a single vector species, Culex quinquefasciatus.[1] LF is a major public health problem globally because 120 million people are infected and 1.25 billion people are at the risk of infection with these parasites in 83 endemic countries in tropical and subtropical regions. India alone contributes 40% of the global burden of this disease and there are approximately 21 million people with symptomatic filariasis and 27 million who have asymptomatic microfilaremia.[2] Furthermore, the disease prevalence is alarmingly the highest among the most productive age class of 15–44 years,[3] which will affect the productivity of the affected communities. The major cause (>90%) of LF in India is W. bancrofti with B. malayi contributing a minor proportion, occurring mainly in small pockets of Orissa and Kerala states. LF is responsible for over 1% of all Diasability Adjusted Life Years (DALYs) lost due to infectious and parasitic diseases and the global estimate of the disability associated with LF was about 0.85 million DALYs[4] in the year 1996. India contributes 40% to global burden of this disease and 44% of DALYs lost worldwide because of this disease, occur in India.[2] In view of this the World Health Assembly called for the elimination of LF as a public health problem, following the World Health Assembly Resolution 50.29 (WHA 50.29) in 1997 calling on the member states of the World Health Organisation (WHO) to eliminate the disease as a public health problem (Anonymous, 1993) and the Global Programme for the Elimination of Lymphatic Filariasis (GPELF) was established in early 2000.

Filarial infection is a major contributor to the deformity, elephantiasis, which not only affects the health of the affected individuals but also their socioeconomic status; often lifelong. The pathology due to filarial parasites leads to a spectrum of clinical symptoms; fever, subclinical infection, acute adenolymphangitis, lymphedema (of the arms, legs, and breast), chyluria, and tropical pulmonary eosinophilia. Although LF is not associated with any mortality, its various clinical presentations, particularly lymphangitis and elephantiasis of the lower limbs and incapacitating genital deformities (hydrocele of the scrotum, in particular), are responsible for heavy functional, psychosocial, and esthetic consequences.

Dirofilariasis affects both domestic and wild animals around the world, with canines as the principal reservoir host. It is transmitted by mosquitoes (Aedes aegypti, Armigeres subalbatus, and Mansonia spp.) as the vectors. Cases of zoonotic dirofilariasis infection, caused by Dirofilaria repens, occur widely throughout European, African, Middle Eastern, and Asian countries.[5] Human dirofilariasis due to D. repens is a common zoonotic infection in Sri Lanka, although Dirofilaria immitis is present in neighboring countries, such as India and Malaysia.[6] In India, reports of subconjunctival infection with D. repens infection in humans are limited.[7] Cases of ocular dirofilariasis, an emerging zoonosis, have been reported from the state of Assam presenting as periorbital and subconjunctival cysts.[8] Human dirofilariasis caused by D. immitis and D. repens have been reported in Malaysia and Hungary.[910] Human ophthalmic dirofilariasis is an uncommon condition, but there have been reports from many parts of the world, including Africa, Australia, the Americas, Europe, and Asia. The parasite is either encysted in a subcutaneous nodule or located under the bulbar conjunctiva.[11] Ophthalmic involvement with Dirofilaria may present itself as periorbital, subconjunctival, orbital, or intraocular infection with lateral rectus muscle involvement.[12] Loa loa is another filarial parasite endemic in the tropical rain forests of western, central, and eastern Africa and is transmitted by Chrysops fly bites. Sporadic cases of loiasis have also been diagnosed in travelers and migrants.[1314] The presence of adult worms under the sclera of the eye frequently manifests as episodic angioedema and periocular migration of adult worms.[15] Rare cases of ocular loiasis have also been reported from India.[16] A characteristic feature of human loiasis is that only adult worms occur in subcutaneous tissues of certain proportion of individuals, whereas circulating microfilariae also occur in others.

As stated above, the most common sites of infection with LF are the lower limb and the genitals. But, reports of infection in uncommon sites appear to be increasing probably because of the awareness and reporting systems. In the present issue, 3 reports deal with infections of subcutaneous area of eye lid, lower arm (medial aspects of right lower arm), and coexistence with neoplastic lesions. While in the case of infection of the eye lid it was with D. repens, the other 2 infections appear to be with the lymphatic filarial parasite, W. bancrofti. The report on the rare co-existence of neoplastic lesions with microfilariae is interesting.

Nodules were generally elongated, nontender, and firm in one case, whereas it was soft, cystic with associated tenderness in the other. In another report among the cases examined some of them were peripheral blood smear (PBS) positive, whereas others were negative. This is a complex issue; some of them might be harboring paired filarial worms and others may be having male and female worms isolated in different locations. Generally, cases with PBS had clinical symptoms of LF, which is on the expected lines. In any case, such cases need to be subjected to appropriate antifilarial chemotherapy. On the other hand, infections manifested as nodules need not be subjected to unnecessary chemotherapy as removal of the worm is adequate. Another major issue is the identification of the parasites in these investigations. The identification should be confirmed by polymerase chain reaction (PCR) assays. I have received the worms from quite a few cases from different hospitals and felt that due to the conditions of the parasites in which they are received it is always better to supplement the diagnosis with PCR assays for unequivocal parasite identification.

While classical cases of filariasis are common and hence dealt at epidemiologic scales, uncommon infections are largely neglected and reported rarely. It is possible that infections especially of dirofilariasis might be more common in areas where stray dog and cat populations occur in large sizes. When one searches for the reports in the literature it is not uncommon to find a few thousands of such reports. This is only a tip of iceberg and indicates the occurrence of large number of cases that go unreported. In view of this it is necessary that the data on such cases need to be generated in a systematic epidemiologic study. This will help in assessing the dimension of the problem and devising strategies for the control.