Data: What is the trend in the disease burden of vector borne diseases in India?
Sai Krishna Muthyanolla
August 26, 2022
India traditionally has seen a high burden of vector-borne diseases such as Malaria, Dengue, Chikungunya, Japanese Encephalitis among others. While significant progress has been made in controlling some, the same is not the case with diseases like Dengue.
The outbreak of COVID-19 demonstrated how disease outbreaks impact a nation. Every sector of the nation was affected, be it the economy, tourism, people, livelihoods, and trade. It is therefore important to understand the disease lifecycle. Adequate research and budgeting coupled with infrastructure provisioning must be done to ensure such outbreaks do not become uncontrollable.
India is one of the high disease burdened countries in the world. It ranks second in the early deaths due to PM 2.5, the leading contributor to global tuberculosis cases,  3% of global malaria burden, and contributes significantly to cases of non-communicable diseases across the world. In addition to this, seasonal outbreaks like malaria, dengue, and other viral diseases have become endemic to several parts of the country. In today’s story, we look at the data regarding vector-borne diseases in India and their trend.
Malaria
Malaria is caused by Plasmodium parasites that are transferred from infected female Anopheles mosquitoes to humans through their bites. The two most dangerous parasite species, P. falciparum and P. vivax, are among those that cause malaria in humans. In African continent, P. falciparum is predominant while P. vivax is common in countries other than sub-Saharan Africa.
Globally, around 241 million malaria cases were reported in 2020, an increase from 227 million in 2019, as per the World Malaria Report 2021. Diseases due to P. Vivax decreased from 18.5 million (8%) in 2000 to 4.5 million (2%) in 2020.  India contributes to 83% of the malaria cases and 82% of malarial deaths in the Southeast Asian region. Sri Lanka and China, in this region, are declared malaria-free by the World Health Organization (WHO).
India also aims to become Malaria free by the year 2022. All of the States and Union Territories (UTs) in the country are split into three categories in accordance with the National Framework for Malaria Elimination (NFME) India, 2016–30, which was launched in February 2016 and aims to phase out malaria by the year 2027. By 2020, 15 low burden States (Category 1) are targeted for complete elimination, while the target for 11 States with a moderate disease burden (Category 2) is 2022. For ten States with a heavy load (Category 3), the target year is 2027. Two States, Mizoram with an annual parasite incidence (API) of 4.61 and Tripura (API 2.43), have high malaria incidence rates according to statistics from 2021. API is less than one in all other states. However, several districts in six States (Chhattisgarh, Jharkhand, Maharashtra, Meghalaya, Odisha, and West Bengal) do have more than one API.
Incidence of Malaria in India
India has made significant progress in controlling malaria. The annual malaria cases fell from 2.03 million in 2000 to 0.16 million in 2021. These P. falciparum (Pf) cases fell from 1.14 million in 2000 to 0.10 million in 2021. However, the share of P. falciparum cases (%) rose from 38.8% in 2000 to 63.1% in 2021. It can be said that P. falciparum remains the most dominant parasitic species in India.
The number of annual deaths due to malaria also shows a decline. It fell from 932 in 2000 to 90 in 2021. This decline is not continuous, as the period between 2006-2010 showed an increase in malarial deaths.
Declining Annual Parasite Incidence (API) and Slide Positivity Rate (SPR) of Malaria
The annual parasite incidence (API) defined as the number of new infections per year per 1000 population, has been declining constantly from 2.12 in 2001 to 0.12 in 2021. Similarly, the Slide Positivity Rate (SPR), defined as the number of laboratory-confirmed malaria cases per 100 suspected cases examined also fell from 2.31 in 2001 to 0.14 in 2021. These indicators point out the significant progress made in controlling the malarial incidence in India.
6 States account for more than 50% of all malaria cases reported from 2016 to 2021
As mentioned earlier, some states have a high incidence of malaria, and they are categorized as high and medium burdened states. From 2016 to 2021, only six states accounted for nearly half of the total malaria cases reported in India. States like Chhattisgarh, Jharkhand, Odisha, Madhya Pradesh, Maharashtra, and Gujarat accounted for more than 50% of total reported cases. Excepting Gujarat and Maharashtra, most of the eastern parts of India including the Northeastern states are highly malaria disease burdened. Incidentally, all these eastern states are home to significant tribal populations.
Dengue cases continue to be worrisome
It is a viral disease caused by the bite of the Aedes Aegypti mosquito. Usually, it occurs in two forms – Dengue fever and Dengue Haemorrhagic Fever (DHF), out of which DHF is the more severe and could be fatal. While all genders and age groups are equally affected, children are more vulnerable to death during a DHF outbreak.
Unlike malaria, the progress in controlling dengue cases in India has not been as successful. The cumulative cases in reported in India rose from 99,985 in 2015 to 2,05,243 in 2019, thereafter which it fell to 1,93,245 in 2021. The COVID-19 outbreak year 2020 saw a steep decline in the number of cases and deaths reported.
The performance across states is not uniform. Traditionally, high incidence states like West Bengal saw a decline in cases, while states like Uttar Pradesh, Punjab, Madhya Pradesh, Gujarat, Haryana, and Rajasthan saw a big spike in cases in 2021, compared to their earlier trends.
Chikungunya cases continue to be sporadic
The chikungunya virus, which belongs to the family Togaviridae and genus Alphavirus, is what causes the disease. Aedes mosquitoes, especially Aedes aegypti, are the main source of chikungunya transmission. The virus that causes it is carried by the bite of infected mosquitoes, and it is crippling but not lethal. It resembles the dengue disease but has no specific treatment.
There is no specific trend observed when one looks at the chikungunya cases over the last six years. The total number of cases kept increasing and decreasing over the years. It was 3,342 cases in 2015, which rose to 26,364 in 2016, then decreased to 9,756 in 2018, and rose to 11,888 in 2021. The percentage of confirmed cases out of the suspected cases decreased from 18.5% in 2017 to 6.9% in 2022 (provisional, as of 31 May 2022). Traditionally, seven states – Andhra Pradesh, Karnataka, Maharashtra, Madhya Pradesh, Tamil Nadu, Gujarat, and Kerala, account for more than 75% of the total cases, barring a few years. The sudden spike in 2021 is due to the increase in infection in the states of Gujarat, Karnataka, and Maharashtra in an exponential manner.
Japanese Encephalitis and AES cases fall after a rise from 2015 to 2019
Japanese Encephalitis (JE) is spread through the bites of female mosquitoes, particularly those in the Culex tritaeniorhynchus, Culex vishnui, and Culex pseudovishnui groups. It is an arbovirus that mostly affects the central nervous system. It is predominantly zoonotic, with the man serving as an unintentional host. Only farm pigs and wild birds are carriers of the Japanese encephalitis virus, and it is not humanly transmissible. JE is the most common viral encephalitis in Asia with case fatality rates ranging from 0.3% to 60%. Acute Encephalitis Syndrome (AES) also belongs to a similar kind of disease affecting the nervous system.
For the purpose of analysis, cases and deaths of both AES and JE are cumulatively taken. It is observed that from barring 2018, from 2015 to 2019, the number of cases of AES and JE rose. It was 11,584 in 2015, which increased to 17,540 in 2019.  In 2019, the number of cases fell sharply. The number of deaths due to AES and JE declined gradually from 1,584 in 2016 to 290 in 2021, except in 2019 when a slightly higher number of deaths were reported than in the previous year 2018.
A decline in Kala Azar cases in India from 2014
A parasitic protozoan of the genus Leishmania causes the slow-progressing indigenous sickness kala-azar. Leishmania donovani is the sole parasite responsible for this sickness in India. The parasite is frequently detected in bone marrow, spleen, and liver and particularly affects the reticuloendothelial system. It is endemic in the eastern Indian States of West Bengal, Bihar, Jharkhand, and Uttar Pradesh. In 1990–1991, the Government of India (GoI) began a centrally supported Kala-azar Control Programme in the endemic states out of concern for the growing Kala-azar issue in the nation. State governments covered the costs associated with implementation while the GoI provided medications, pesticides, and technical support. The National Health Policy of 2002 established a deadline of 2010 for Kala-azar eradication in India, but that deadline was later changed to 2015.
Though the target of eradicating Kala Azar by 2015 has not been achieved completely, India is on the path to achieving that target sooner. As mentioned above, it is endemic to only a few states in India. The cumulative Kala Azar cases in ten states were 9,241 in 2014, which gradually reduced to 1,276 in 2021 (provisional data), and 533 in 2022 (provisional till July). The number of deaths also fell from 11 in 2014 to 6 in 2020. However, 2021 and 2022 reported an increase in the number of deaths due to Kala Azar.
Filariasis
Several parasitic spherical, coiled, and thread-like worms from the family Filaridea are the cause of filariasis. Nematode worms such as Wuchereria bancrofti or Brugia malayi are the disease’s causative agents.  The illness, which is responsible for a considerable deal of societal shame, frequently presents as odd swelling of the legs and hydrocele. Wuchereria bancrofti, a species, is to blame for 99.4% of cases in India, while Brugia malayi is only 0.6% of the problem. In 18 states and union territories, Lymphatia filaria is a common problem. Brugian filariasis caused by Brugia malayi is only seen in six states—UP, Bihar, Andhra Pradesh, Orissa, Tamil Nadu, Kerala, and Gujarat. Filariasis is endemic in 328 districts across 20 States and Union Territories in India. Among states, Uttar Pradesh tops with 51 districts, followed by Bihar with 38 districts, Tamil Nadu, and Odisha with 20 districts, Jharkhand with 18 districts, and Maharashtra with 17 districts.  About 40% of all cases of lymphatic filariasis (LF) worldwide are caused by India.
To curb Filariasis, the National Filaria Control Programme was launched in 1955. Though initially confined to urban areas, the programme has been extended to rural areas since 1994.  Another campaign to eradicate lymphatic filariasis (ELF) was launched in June 2004. Accelerated Plan for Elimination of Lymphatic Filariasis was launched during the 10 Global Alliance Elimination of Lymphatic Filariasis on 13 June 2018. According to the WHO’s Road Map for Neglected Tropical Diseases (NTDs), the Government of India has set the goal of eradicating lymphatic filariasis (LF) by 2030.
Featured Image: Vector-borne diseases in India