How India Fared In Battling Vector-Borne Diseases In 2024

Two neglected tropical diseases (NTDs)--visceral leishmaniasis and lymphatic filariasis--are on the verge of elimination, as per data from the National Centre for Vector Borne Disease Control (NCVBDC).

Dengue, malaria, Japanese encephalitis and kala azar killed 285 people in 2024, as per data from the NCVBDC. A vaccine was discovered for dengue, and new techniques for vector management that aim to control the breeding of mosquitoes and sandflies were deployed in high-risk areas.

India also struck trachoma--a highly infectious disease that can spread by flies or contact with an infected person--off the list of NTDs endemic to the country. Trachoma was the cause of 4% of all blindness in India. India was declared infective trachoma-free in 2017, but surveillance continued up to 2024.

As 2024 comes to a close, we look at how India fought against vector-borne diseases.

Increasing prevalence

The number of kala azar (visceral leishmaniasis) cases dropped to a tenth of their number in 2018. “For elimination status, India needs to reduce the number of kala azar cases to less than 1 for every 10,000 people,” explained Nirmal Ganguly, microbiologist and immunologist. VL and lymphatic filariasis are no longer public health crises in India, Ganguly, a former director of Indian Council of Medical Research (ICMR), added.

The World Health Organization (WHO) has set 2030 as the elimination goal for both LF and VL. “India has set its own country-target for elimination of LF by 2027 and VL by 2026, respectively,” explained Satyabrata Routray, director of infectious diseases at PATH and advisor to the Uttar Pradesh government.

India reported 621,178 cases of lymphoedema and 127,100 cases of hydrocele, both of which are caused by the filariasis worms, as per the LF/VL newsletter for 2023. This was an increase of 5.9% from 2021, when 705,928 (527,198 lymphoedema and 178,730 hydrocele) cases of filaria were detected. But there was some good news about another mosquito-borne disease, malaria, in 2024.

The country, which accounted for 0.8% of all malaria cases and 0.6% of all malaria deaths in the world in 2023, exited the “high burden high impact countries” group in 2024 due to significant progress in reducing malaria incidence and mortality, as per the World Malaria Report.

Malaria cases continued to increase in 2023, and there were 209,640 recorded up to October 2024. However, this could be an artifact of increased surveillance and testing which results in increased case confirmation, explained Routray.

Surveillance for malaria has increased: the Annual Blood Examination Rate (ABER) increased from 9.58% in 2015 to 11.62% in 2023. (This is the rate of testing blood samples in a population for malaria.)

Malaria case load could also have increased because of alert authorities increasing testing and following heavy rainfall events, he added. “...malaria, like any other vector borne disease, also varies and fluctuates with climate change and rains and flooding that increases vector density…and that requires early detection and prompt treatment of all cases reported so that death from malaria is low.” Unseasonal rains extended malaria’s transmission window in Uttar Pradesh, as IndiaSpend reported in June 2024.

Cases of malaria are expected to decline “with the potential for reaching zero indigenous cases by 2027–2028”, predicted a study that analysed data from 1990-2022. The government aims to eliminate malaria by 2030--defined as zero indigenous cases and interruption of the transmission of malaria, as per the National Strategic Plan 2023-27.

Underreporting of malaria cases can be addressed by increased surveillance and a unified approach to health that takes climate into account, IndiaSpend reported in June 2024.

Dengue cases increased by 83% between 2019 and 2023 and deaths from the disease nearly tripled between 2019 and 2023. The vector responsible for the transmission of dengue, aedes aegypti, finds suitable breeding conditions in heavy rainfall followed by heat, as we reported in November 2024.

A different mosquito-borne disease resurfaced in 2024. India saw 148 cases of acute encephalitis syndrome (AES), an infection of the brain, in 2024. The CHPV, a member of the rhabdoviridae family of viruses transmitted through the bite of a mosquito and sandflies, is one of the causative agents of AES in India and was identified in 51 cases. “This deadly virus is transmitted by the aedes aegypti mosquito, that was first detected in 1965 in Maharashtra, and thereafter has been reported sporadically across many other states,” explained Routray.

This is the same mosquito that is responsible for the spread of diseases like dengue and chikungunya. “AES caused by CHPV has a very high case fatality rate, more than 50% if not treated promptly, and mostly affects children under 15 Years of age, with a clinical symptom complex of high fever with altered sensorium, neurological manifestation and/or convulsions,” said Routray. A reemergence of cases detected in a few states means that this infectious disease needs focused attention and immediate intervention, he added.

Encephalitis caused by CHPV has a higher morbidity than Japanese encephalitis, explained Ganguly. The virus is endemic in central India (Andhra Pradesh, Vidarbha in Maharashtra).

Vaccine for dengue in two years, surveillance and treatment for others

A vaccine for CHPV was too expensive, and therefore there was no commercial interest in developing it, according to Ganguly. However, phase 3 clinical trials for DengiAll, a tetravalent vaccine candidate produced by Panacea Biotec in partnership with ICMR, were announced in August 2024.

“The trial will follow participants for two years, and based on the efficacy results a decision will be made on the licensure of this vaccine, following which DengiAll should be available to Indian population,” explained Routray, adding that the decision to provide the vaccine nationwide or in disease hotspots will be made based on evidence of disease incidence and other parameters.

The success of Iran, India and Sri Lanka in controlling the anopheles stephensi mosquito--an efficient vector of Plasmodium falciparum and P. vivax which cause malaria--prompted the WHO to compile their experience in 2024. At the same time, Odisha fell short of insecticidal nets, a key weapon in the fight against malaria, as we reported in July 2024.

Scrub typhus, a disease spread by the bite of the chigger mite, also causes AES. Scrub typhus is not included in the mandate of the NCVBDC yet. “Scrub typhus is an important cause of fever of unknown origin. If we make it notifiable, we can expect that people will report it and we will know its extent at the national level and undertake measures to treat and prevent it,” explained Yogesh Kalkonde, public health practitioner and executive committee member at Sangwari, a group that works to provide healthcare services in rural Chhattisgarh.

An increase in relative humidity caused an increase in the cases of scrub typhus, while high temperatures may cause a decrease. Nevertheless, an increase in the interactions between human beings and wildlife will cause an increase in the number of scrub typhus cases, according to Kalkonde.

Despite having a test for it, scrub typhus can get missed and the diagnostic test for it may not be easily available in rural areas where this disease is common, and due to lack of early diagnosis and treatment, is misdiagnosed and untreated because it oftenfrequently presents with multi-organ complications, according to Kalkonde. “Doctors need to include scrub typhus in their list of potential causes of fevers and prescribe the right first-line drug that can treat it instead of resorting to higher antibiotics for other diseases when their patients’ fevers do not subside,” he explained.

In response to scrub typhus, the state of Uttar Pradesh increased surveillance and investigation of high grade fevers, setting up encephalitic treatment centers that provide antibiotics, cleaning of ponds and drains and cutting of shrubs, said Routray.

Efforts to control filariasis spread bore fruit at the district level. Residents of 63 high burden districts in Bihar, UP, Jharkhand, Karnataka, Odisha and Telangana were given the antifilarial drug in the second phase of mass drug administration. LF was endemic in 345 districts of 20 states in the country, of which 138 saw reduced transmission and stopped the mass administration of the antifilarial drug in 2024.

Drugs used in the treatment of dermal kala azar impacted patients’ eyesight, as we reported in March 2024. Drug and vaccine research, increased surveillance and testing is crucial in the fight against neglected tropical diseases, as we reported in September.

IndiaSpend has written to the National Centre for Disease Control and the NCVBDC on the number of cases of LF and scrub typhus in 2024, on making scrub typhus a notifiable disease, the increase in testing for malaria in the affected states and the measures taken to control the transmission of dengue, chikungunya and lymphatic filariasis. This story will be updated when we receive a response.

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