Bangladesh eradicates kala-azar, India on track too but challenges remain

Visceral leishmaniasis (VL) also known as kala-azar, is caused by protozoan parasites transmitted by the bite of an infected female phlebotomine sand fly.

New Delhi: Bangladesh recently achieved a major public health goal when it eradicated visceral leishmaniasis, commonly known as kala-azar, raising the question of when India would wipe out the debilitating, often fatal, parasitic disease – the fight very much on but far from complete.

Challenges in sustaining the momentum of the fight persist, particularly in tackling post-disease symptoms and HIV co-infections, experts said as the ‘LV spotlight’ swivelled to India.

“Disease incidence has gone down to approximately 463 in 2023 from the previous 44,533 in 2014, a 99 per cent decrease in case numbers,” said Shyam Sundar, programme director of the Kala-Azar Medical Research Centre in Bihar, one of the four states most affected by the disease.

"The spotlight is currently on India as we eagerly await its announcement,” Kavita Singh, director, South Asia, Drug for Neglected Diseases Initiative (DNDi), told PTI.

Visceral leishmaniasis (VL) is caused by protozoan parasites transmitted by the bite of an infected female phlebotomine sand fly. It is characterised by irregular bouts of fever, weight loss, enlargement of the spleen and liver, and anaemia. In over 95 per cent of cases, the disease is fatal if left untreated.

There are three main forms of leishmaniasis: visceral (the most serious form because it is almost always fatal without treatment), cutaneous (the most common, usually causing skin ulcers), and mucocutaneous (affecting mouth, nose and throat).

Globally, most cases occur in Brazil, east Africa and India. An estimated 50,000 to 90,000 new cases of VL occur worldwide annually, with only 25–45 per cent reported to WHO.

Confident that India is on course to eliminating the disease, experts emphasise that efforts and continued vigilance are essential to overcome the hurdles in the way of lasting victory.

The challenges are plenty. And amongst the most formidable is post kala-azar dermal leishmaniasis (PKDL), which occurs in individuals who have apparently been cured of VL. Such patients develop skin lesions that are variable in location and intensity.

However, as they appear on the skin, the sand fly vector can comfortably sit on a skin lesion, take a juicy blood meal and thereafter bite uninfected individuals who will then develop VL, and so the vicious cycle will continue.

While the country looks on course to eliminate the disease, experts emphasise the importance of addressing PKDL in tandem with VL to sustain elimination.

“This is the cycle we need to interrupt by diagnosing and treating VL and PKDL and also insecticidal spraying in endemic areas. So PKDL cases are considered as the disease reservoir, and are strong disease transmitters,” said Dr Mitali Chatterjee, professor of Pharmacology at Kolkata’s Institute of Postgraduate Medical Education & Research (IPGMER).

She said the reservoir continued to expand because PKDL was initially not accorded the same priority as LV.

“However, now there is active surveillance for both VL and PKDL and the scenario in another two-three years will change dramatically for the better, as both PKDL and VL cases are being detected and treated. Also, there is very good vector management and the sand fly density will also see a decline,” she added. Sundar agreed.

Describing PKDL as a chronic disease, he said it is a threat to a new kala-azar epidemic and underscored the need to for active detection and treatment of such cases.

India recorded 286 PKDL cases from January to October this year, a significant decline from 616 in 2022.

Another big threat to VL elimination is HIV-kala-azar co-infection which has an incidence of 6 per cent of total cases. There are currently 530 cases of HIV- VL, according to data from the National Centre for Vector Borne Diseases Control.

“These patients readily infect the sand flies and have parasites everywhere in the body, in circulating blood as well. These patients should be treated efficiently and promptly,” Sundar said.

The problem with these cases, the expert noted, is that they repeatedly relapse, adding they have to be closely followed. As soon as a relapse is detected, prompt treatment should be provided.

“Treatment of HIV infection with antiretroviral (HIV drugs) is of paramount importance to postpone or prevent relapses,” said Sundar.

DNDi’s Singh warned that kala-azar has the tendency to strike back, as it did in the 1960s and the current dependence is only on one treatment.

“It is important to focus on treating PKDL and VL-HIV co-infections for achieving sustainable elimination. Some of these treatments are lengthy and toxic,” Singh said.

“After a few years that treatment might not work well because of resistance. So we need new drugs. DNDi continues to drive R&D and innovation in search of better treatments and diagnostics for kala-azar and other neglected tropical diseases including oral drugs to support sustainable elimination of visceral leishmaniasis,” she added.

Much of the success of India’s fight against LV is attributed to the role of anti-fungal drug liposomal amphotericin B.

"The availability of a single infusion of liposomal amphotericin B proved to be the game changer that VL needed; it dramatically brought down the cases,” Chatterjee told PTI.

Echoing her in crediting the drug for the success in combating LV, Sundar said US-based biopharmaceutical company Gilead Sciences, through the World Health Organization, had donated 4,45,000 doses free to the country. This was then adopted in the control programme in 2013.

India has the world's largest absolute burden of at least 10 major NTDs (neglected tropical diseases) -- hookworm, dengue, lymphatic filariasis, leprosy, kala-azar and rabies, ascariasis, trichuriasis, trachoma and cysticercosis.

Union Health Minister Mansukh Mandaviya said in January this year that there has been a 98.7 per cent decline in cases of kala-azar -- from 44,533 in 2007 to 834 in 2022 in India. He reiterated the country’s commitment to eradicating the disease by end of the year.

Up to October this year, India had 463 cases of VL and four deaths, with Bihar (293) and Jharkhand (148) still in triple digits. West Bengal and Uttar Pradesh had just 12 and 16 cases respectively. Sikkim had two cases.

In a monumental achievement, WHO on October 31 announced that Bangladesh was the first country in the world to eliminate visceral leishmaniasis as a public health problem. This was successfully validated based on the fact that the number of reported cases of the disease was below 1 per 10,000 people in each of the country’s subdistricts for at least three consecutive years.