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Data: What has been the trend in incidence of Vector-Borne Diseases in India?

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Lakhs of people in India are affected by vector-borne diseases every year. But what has been the trend in the incidence of these diseases over the years? Are there differences between states? Here is a review.

Globally, more than 7 lakh deaths occur annually from vector-borne diseases such as malaria, dengue, yellow fever, Japanese encephalitis, and others. Vector-borne diseases are caused by parasites, viruses, and bacteria that are transmitted by vectors. According to WHO, tropical and subtropical areas are the most affected by such diseases and the poorest populations are the most vulnerable. Not only do vector-borne diseases claim lives but diseases such as Lymphatic Filariasis, Kala Azar, etc. can result in chronic suffering, disability, and even stigmatization. 

National Vector Borne Disease Control Programme was launched in 2003-04

In India, for the prevention, control, and elimination of vector-borne diseases such as Malaria, Dengue, Kala Azar, Lymphatic Filariasis, among others, the National Vector Borne Disease Control Programme (NVBDCP) is being implemented. The programme was launched in 2003-04 by merging the National anti-malaria control programme, National Filaria Control Programme and the Kala Azar Control programme. NVBDCP is also an integral component of the National Health Mission which envisages the achievement of universal access to equitable, affordable, and quality health care services that are accountable and responsive to people’s needs. 

In this story, we look at the status of five vector-borne diseases (Leprosy, Kala Azar, Lymphatic Filariasis, Malaria, and Dengue) in India which continue to affect thousands of people every year. 

India has highest burden of leprosy despite reducing prevalence to less than 1 case per 10,000 population

India achieved the goal set by the National Health Policy, 2002 of elimination of leprosy as a public health problem, by bringing down the prevalence of the disease to less than 1 case per 10,000 population at the National level in December 2005. In spite of this, India has the highest burden of leprosy cases. 

According to a Lok Sabha response from February 2021, there were 133 endemic districts identified for leprosy elimination (less than one in ten thousand cases) in 2017-18 which reduced to 120 in 2018-19 and 107 in 2019-20. The reason for the larger number of districts in 2017-18 and 2018-19 is due to the detection of a higher number of leprosy cases through intensified active case search campaigns, as per the Lok Sabha response.  

Four states accounted for more than half the cases reported in India

According to the Annual Report on Leprosy for 2019-20, by the end of March 2020, a total of 1.14 lakh cases were reported, a reduction of nearly 5% as compared to March 2019. In terms of the number of cases, Bihar and Maharashtra had reported more than 16,500 cases each in 2019-20 followed by Uttar Pradesh with more than 15,000 cases and Odisha with more than 10,000 cases. Together, these four states alone accounted for about 51% of the Leprosy cases reported in 2019-20. 

Prevalence of leprosy is highest in Chhattisgarh among states

The overall prevalence rate of the disease in India is 0.57 per 10,000 population. This can be interpreted as 5 to 6 persons out of one lakh persons in India have been diagnosed with Leprosy. However, the prevalence rate per 10,000 population shows that the disease was the most prevalent in Dadra and Nagar Haveli with nearly 3 persons out of 10,000 population being diagnosed with Leprosy. Of the states, Chhattisgarh has the highest prevalence across the states with 2.08 followed by Odisha with a prevalence rate of 1.45. All the other states have a prevalence ratio below 1 per 10,000 population. 

Number of reported Kala Azar cases have reduced over the years

The number of cases of Kala Azar, an infection that mainly affects visceral organs, has also dropped over the years. In 2017-18, there were a total of 54 endemic districts which dropped to 14 in 2018-19, 8 in 2019-20, and only 5 in 2020-21 (As of November 2020). Meanwhile, the overall number of cases has dropped gradually from 13,869 in 2013 to over 4,380 cases in 2018. Provisional data for 2019 shows only 3145 cases were reported and in 2020, less than 2000 cases were reported.  

Cases were reported across seven states in 2013 and 2014 whereas, since 2017, the number of states reporting cases of Kala Azar dropped to 5 and further down to four states in 2018 including Bihar, Jharkhand, Uttar Pradesh, and West Bengal. Bihar accounted for more than 78% of the cases in 2018. The number of cases of Kala Azar per 10,000 population is also highest for Bihar as compared to other states, though the number of cases has decreased even here over the years. 

Lymphatic Filariasis is endemic to 16 states/UTs making over 650 million persons vulnerable

Lymphatic Filariasis (LF), also commonly known as elephantiasis, is a disfiguring disease that is usually acquired in childhood. Filariasis has been a major public health problem in India next only to malaria. India contributes to nearly 40% of Lymphatic Filariasis cases globally. The disease is endemic in 257 districts of 16 States & 5 UTs including Andhra Pradesh, Assam, Bihar, Chhattisgarh, Goa, Jharkhand, Karnataka, Gujarat, Kerala, Madhya Pradesh, Maharashtra, Orissa, Tamil Nadu, Uttar Pradesh, West Bengal, Pondicherry, Andaman & the Nicobar Islands, Daman & Diu, Dadra & Nagar Haveli and Lakshadweep. About 650 million people in these States/UTs are at risk of developing it. States of Bihar, Jharkhand, Uttar Pradesh, and Odisha contribute the highest number of LF cases, as stated in a Lok Sabha response. NorthWestern and North Eastern states are considered to be free from indigenously acquired filariasis. Currently, the disease has been eliminated from about 98 districts and non-endemic districts are being re-mapped in endemic states.

Cases and deaths due to Malaria have reduced significantly in India in the last two decades

With nearly 95% of the population residing in Malaria endemic areas, Malaria has been a major public health problem in India, and in other regions such as sub-Saharan Africa, South-East Asia, Eastern Mediterranean, Western Pacific, and the Americas. India has made significant progress in tackling this disease. The number of cases of malaria has dropped from over 3 million cases in 1996 to around 0.34 million in 2019. During the same period, the number of deaths due to Malaria has also dropped from more than 1,000 cases to less than 100 each year during this period.

API continues to be within target, but ABER target is not being maintained

Annual Parasite Index (API) is the measure used to calculate the prevalence of Malaria. API is malaria positive cases per thousand population. In 2001, India’s API was 2.12 which meant that more than 2 people out of 1000 population were infected with Malaria. Since 2012, India has been maintaining the API below 1. In 2019-20, India’s API was 0.25. As per the latest state-wise data available, six states had an API greater than 1 as of 2018. Mizoram and Tripura had API greater than 3, followed by Chhattisgarh with an API of 2.63. Meghalaya, Jharkhand, and Odisha had recorded an API greater than 1 in 2018. 

ABER on the other hand is the Annual Blood Smear Examination Rate calculated as the percentage of blood smears examined in a year of the total population. Under the presumption that at least 10% of the population will have a fever at any point in time in a year, the ideal ABER is considered 10% and above. But India’s overall ABER has crossed 10% only once in 2014. It has been between 8.5% to below 10% in the rest of the years. Across the states, Gujarat had the highest ABER of over 23% followed by Goa with 23% as of 2018. 15 states and UTs had ABER greater than 10%. The proportion of samples tested in Bihar was the least with an ABER of only 0.13%. Delhi also had an ABER below 1%. 

Case Fatality Ratio of Dengue is being maintained below 1% across states

Dengue is a viral disease that is also mainly found in tropical and sub-tropical regions. Lakhs get infected every year. The number of cases in India has been more than 1 lakh each year between 2016 and 2019 while the number of deaths due to the disease has decreased. 

Case Fatality Ratio (CFR) is the ratio of the number of deaths reported due to dengue to the total number of cases reported is calculated. The target is to sustain a CFR below 1%. At the national level, India has successfully maintained this between 2017-18 and 2019-20. Even across states, most states and UTs have managed to maintain the CFR below 1% since 2017.

Behavioural change, availability of facilities, and improved WASH are required

The causes for vector-borne diseases can be unplanned urbanization, environmental damage, and the unavailability of basic amenities for all. The outbreak of such diseases hinders development & economic activity & increases the financial burden on many vulnerable families. Behavioural changes, improved water and sanitation systems, etc. are required for the prevention of such fatal diseases. It is necessary that the fatalities and number of cases are brought down to meet the health targets under the SDGs by 2030. 

Featured Image: Vector-Borne Diseases in India

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