India witnesses decline in vector-borne tropical diseases in last 2 years

India has seen a decline in major vector-borne diseases like lymphatic filariasis (elephantiasis, haathipaon), leishmaniasis (kala-azar), dengue and chikungunya in the last two years, according to data from the National Centre for Vector-Borne Diseases Control (NCVBDC). The drop is despite the global challenges posed by neglected tropical diseases (NTDs) which impact over 1 billion people globally. NTDs are a diverse group of tropical infections that typically affect the marginally low-income groups. NCVBDC numbers reveal a downward trend in these diseases over the past few years, indicating successful control efforts.

Leishmaniasis cases declined from 1,276 in 2021 to 520 in 2023 (till September). Similarly, chikungunya cases dropped from 11,890 in 2021 to 3,711 in 2023 (till September), while dengue cases fell to 94,198 in 2023 from 193,245 in 2021.

“Lymphatic filariasis (LF) is a unique challenge as it leads to chronic debilitating conditions like lymphedema and hydrocoele, which remain even after the disease is treated. As of 2022, 550 thousand lymphoedema cases and 150 thousand hydrocoele cases were present in India. Therefore, LF requires enhanced surveillance, and proactive and preventive strategies like Mass Drug Administration (MDA) to prevent chronic manifestations and disability development,” said Manju Rahi, Director, Vector Control Research Centre of the Indian Council of Medical Research (ICMR).

Data from NCVBDC also revealed that the cases of vector-borne NTDs in India such as leishmaniasis, a parasitic infection causing skin sores, declined 59.2 per cent from 1,276 cases in 2021 to 520 cases in 2023. Similarly, mosquito-borne illnesses such as dengue and chikungunya also dropped by 51.3 per cent and 68.8 per cent, respectively in the same period.

Last August, the government of India while inaugurating the second phase of the Annual Nationwide Mass Drug Administration initiative announced its plans to eradicate lymphatic filariasis, a parasitic disease caused by microscopic, thread-like worms by 2027, surpassing the global target by three years.

The MDA initiative commenced in 2004, initially employing a single dose of diethylcarbamazine citrate (DEC). In 2007, the strategy evolved with the co-administration of DEC and albendazole. Subsequently, in 2018, the triple-drug therapy (IDA), comprising DEC, albendazole, and Ivermectin, was introduced in five selected districts. As the elimination target draws near, the focus has shifted to encompassing all remaining districts.

The annual MDA involves administering a single dose of DEC and albendazole to eligible individuals aged 5 years or more (excluding pregnant women, children below 2 years, and seriously ill individuals), aiming to interrupt the transmission of the disease.

AP Dash, Vice Chancellor of the Central University of Tamil Nadu stated, “India's progress in eliminating NTDs has been commendable, with concerted efforts targeting specific diseases like lymphatic filariasis, visceral leishmaniasis (kala azar), and leprosy. LF elimination efforts have been particularly successful through MDA programmes, where health workers administer free-of-cost preventive medicines door-to-door.”

In the case of visceral leishmaniasis, there has been a remarkable decline of over 94 per cent in cases since 2014, indicating substantial progress toward elimination,” Dash said, adding efforts to combat leprosy have also seen advancements, although challenges remain in reaching remote and marginalised populations.

"Vector-borne NTDs like dengue and chikungunya are spreading nationwide, penetrating peri-urban and rural areas. This can be attributed to changing behaviours in areas where penetration of plastic use has increased, alongside poor waste clearance. The risk map for dengue and chikungunya is expanding, while kala azar is reported in Bihar, Jharkhand, Uttar Pradesh, and West Bengal, with sporadic cases in Sikkim and Kerala. Lymphatic filariasis remains endemic in 20 states, with endemic districts rising from 328 in 2021 to 333 in 2023," Rahi said.

According to the World Health Organisation, NTDs are caused by various pathogens including viruses, bacteria, parasites, fungi and toxins. NTDs affect more than 1 billion people worldwide, while the number of people requiring NTD interventions both preventive and curative stands around 1.6 billion.