Neglected Tropical Diseases

Neglected tropical diseases (NTD) are a group of diverse communicable diseases that cause high morbidity and mortality in people from low/middle income countries, including India. The World Health Organization identified 20 NTDs and India leads the world in the total number of cases for at least 11 major NTDs. Lymphatic filariasis and visceral leishmaniasis are among the major NTDs and accounted for 29% and 45% of the global cases in 2016, respectively.

Lymphatic filariasis

Lymphatic filariasis or elephantiasis, is a parasitic infection spread by mosquitos. In India, it is caused by the parasitic filarial worms Wuchereria bancrofti (>90% of the cases) and Brugia malayi. The adult worms reside in the lymphatic system of humans. Female worms produce microfilariae, which appear in the peripheral blood during the night and are ingested by mosquitoes along with a blood meal. Microfilariae undergo development within the mosquito to infective stage larvae, which are transmitted from mosquito to humans during blood feeding. The larvae move to lymphatic vessels and develop into adult worms. The parasites infect children in early life although symptoms appear later in their adult life.

Symptoms

Lymphatic filariasis infection causes asymptomatic, acute, and chronic conditions.

Asymptomatic
  • No external signs of infection
  • May damage the lymphatic system
  • Affects the immune system
Acute
  • Local inflammation involving lymph nodes, lymphatic vessels and skin
  • Occurs as a result of secondary bacterial skin infection when the underlying lymphatic damage suppresses the immune system
Chronic
  • Tissue swelling (lymphoedema)
  • Skin/tissue thickening of limbs (elephantiasis)
  • Scrotal swelling (hydrocele)
Transmission
  • Transmission of the parasite to humans occurs by various genera of mosquitoes in different geographical locations
  • In India, Culex quinquefasciatus is the major vector
Prevention and Control
  • The global program for the elimination of lymphatic filariasis involves mass drug administration (MDA), integrated vector management and morbidity management and disability prevention
  • The World Health Organization recommends annual MDA comprising diethylcarbamazine with albendazole (DA) in communities without onchocerciasis
    • Under special circumstances, annual ivermectin plus diethylcarbamazine plus albendazole (IDA) is recommended instead of DA
Current Status
  • India is committed to eliminating lymphatic filariasis by 2027
  • In 2021, a total of 525,440 lymphoedema and 144,645 hydrocele cases were reported
    • Most of the lymphedema cases were reported from Bihar, Uttar Pradesh, Odisha and Telangana
    • Most of the hydrocele cases were reported from Odisha, Jharkhand, Uttar Pradesh and Bihar
References

Visceral leishmaniasis

Visceral leishmaniasis or kala-azar, is caused by protozoan parasites of different Leishmania species in distinct geographical areas and is spread by sandflies. In India, visceral leishmaniasis is caused by Leishmania donovani. Leishmania exists in two different morphological stages: the extracellular motile promastigote in the sand fly and the intracellular amastigote in humans. The sand flies inject the promastigotes into humans during blood meals. Promastigotes are ingested by phagocytic cells in humans where they transform into amastigotes and multiply. The infected cells eventually burst and release amastigotes, which in turn infect other phagocytic cells. Sand flies become infected by ingesting infected cells during blood meals. Amastigotes transform into promastigotes within the gut of sand flies and migrate to the proboscis for transmission during the next blood meal. The incubation period ranges between 2 weeks to 8 months. Visceral leishmaniasis is fatal within 2 years if left untreated.

Post-kala-azar dermal leishmaniasis (PKDL) is a nonlethal dermal condition that occurs in 10%-20% of patients in Asia after treatment of visceral leishmaniasis. Leishmania parasites reside within skin lesions and can be transmitted through the bite of sand flies.

Symptoms

Most infections are asymptomatic; symptoms appear in 2%-23% of infected individuals within a year.

  • Persistent irregular fever
  • Weight loss
  • Enlargement of the spleen (splenomegaly)
  • Enlargement of the liver (hepatomegaly)
  • Low blood counts (pancytopenia); including low red blood cell counts (anaemia), low white blood cell counts (leukopenia) and low platelet counts (thrombocytopenia)
  • Darkening of the skin (hyperpigmentation) of the face, hands, feet and abdomen
Transmission
  • The Leishmania parasite is transmitted to humans through the bite of infected female sandflies (Phlebotomus argentipes)
Treatment
  • The Asian elimination initiative adopted miltefosine in 2005 as the first-line regimen; however, recent evidence of reduced effectiveness has resulted in alternative treatment strategies
  • In the Indian subcontinent, treatment with single-dose liposomal amphotericin B (LAMB) is recommended as part of the elimination initiative
  • Other treatment options include LAMB plus miltefosine or paromomycin; miltefosine plus paromomycin; and amphotericin B deoxycholate
Current Status
  • India is committed to eliminating visceral leishmaniasis by 2023
  • India has seen a steady decline in the number of cases of visceral leishmaniasis from 9241 in 2014 to 1276 in 2021
  • In 2021, more than 90% of the reported cases were from Bihar and Jharkhand
References