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Data: Number of cases of ‘Vector-Borne Diseases’ increase in 2021 after a fall in 2020

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Vector-borne diseases are a common form of infectious disease in India & across the world accounting for a significant number of deaths. Data indicates that the incidence of vector-borne diseases in India reduced in 2020 across most of the diseases only to increase in 2021. COVID-19 could have played a major role in the reduced numbers in 2020. 

The World Health Organization (WHO) defines Vector-borne diseases as “human illnesses caused by parasites, viruses and bacteria that are transmitted by vectors.” Globally, these diseases account for more than 17% of all infectious diseases and cause more than 7 lakh deaths annually. 

The WHO lists various diseases as Vector-borne diseases. In India – Malaria, Dengue, Chikungunya, Japanese Encephalitis (JE), Kala-azar & Lymphatic Filariasis are considered as Vector-borne diseases (VBDs). 

Responding to a question in Rajya Sabha in November 2021, the Ministry of Health and Family Welfare furnished the details of the prevalence and the deaths attributed to various VBDs over the past 3 years along with the provisional figures for the current year.  In this story, we look at this data and analyse the trends for each of these diseases. 

Malaria

The number of cases of Malaria fell by around 45% in 2020 compared to 2019. In 2020, around 1.86 lakh cases of Malaria were reported, whereas in 2019 the number was around 3.38 lakhs. 

In fact, there is a declining trend of Malaria cases in the country as the number has been reducing since 2018 when 4.29 lakh cases were reported. 

As per the provisional data until September 2021, around 1.07 lakh cases of Malaria were reported in 2021. While the number of cases of Malaria reduced significantly in 2020, the number of deaths increased to 93 compared to 77 in 2019.  

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 Here is a snapshot of Cases & Deaths relating to Malaria across the States & UTs: 

  • During 2018 & 2019, Uttar Pradesh reported the greatest number of Malaria cases with 86.48 thousand and 92.73 thousand respectively. However, there was a steep fall in the number of cases in 2020 and reached 28.6 thousand. No Malaria related deaths were reported from UP during any of these years. 
  • A similar trend is observed in the case of Jharkhand, Madhya Pradesh & Gujarat, where the number of cases has continuously decreased over the years.  
  • While the number of cases reported in Chhattisgarh has also continuously decreased, the state has replaced UP as the state with the greatest number of Malaria cases in 2020. 
  • Among the other states with a higher prevalence of Malaria, the decrease in the number of cases is not so prominent in Odisha. In fact, the number of Malaria cases in 2020 increased in the case of Odisha. 
  • On the other hand, the number of cases in Maharashtra increased from 10.7 thousand in 2018 to 15.2 thousand in 2020. 
  • Despite its lower population, Tripura reported a high number of Malaria cases. 
  • Between 2018 & 2021, Chhattisgarh accounted for most of the deaths. The state reported 127 deaths because of Malaria, which is more than 1/3rd the total number of deaths (311) in the country during this period. 

Dengue 

Like in the case of Malaria, the number of cases of Dengue in 2020 was considerably lower than the previous years. In 2019, around 2.05 lakh dengue cases were reported in the country, which reduced to 44.5 thousand cases in 2020. As per the provisional data available until November 2021, the number of cases of Dengue in 2021 has again increased to 1.64 lakhs. Compared to Malaria, Dengue resulted in a higher fatality. However, the trends indicate a fall in fatality rates compared to 2018. 

Here is a snapshot of cases & deaths relating to Dengue across the States & UTs: 

  • The increase in the number of cases during 2019 can be attributed to the increase in the number of Dengue cases reported in West Bengal. The number of cases in the state increased from 23.3 thousand in 2018 to 47.92 thousand in 2019. Gujarat & Karnataka also contributed towards the increase in 2019. 
  • The number of cases fell drastically in West Bengal in both 2020 and 2021.
  • The fall in the number of Dengue cases in 2020 is seen across the states. 
  • Despite the lower numbers in West Bengal in 2021, the increase of Dengue cases in 2021 (until November 2021) is driven by the increase of cases in UP, Punjab, Rajasthan, MP, Maharashtra, Haryana, and Delhi among others. 
  • West Bengal & Maharashtra contributed to a majority of deaths during 2018 & 2020. In 2021, Rajasthan reported 70 of the 146 deaths reported nationally. 

Chikungunya 

Even in the case of Chikungunya, the number of cases recorded has reduced in the year 2020. 

In 2018, 57.8 thousand cases of Chikungunya were reported across the country which increased to 81.9 thousand in 2019. In 2020, the number of Chikungunya cases fell to 43.4 thousand. However, as per the provisional information available as of 21 November 2021, the number of Chikungunya cases increased to around 93.3 thousand cases in 2021. 

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  • Karnataka consistently has the greatest prevalence of Chikungunya cases in the country. In 2019, more than half the cases in the country were reported from Karnataka with 43.69 thousand cases out of the 81.91 thousand across the country. Even in the current year (2021), Karnataka reported more than 1/3rd of the total cases in the country. 
  • Gujarat has the second-highest prevalence in 2021 with 27.3 thousand cases, followed by Maharashtra with 16.7 thousand cases. These three constitute more than 80% of the cases in the country in 2021. 
  • UT of Puducherry also reported a high number of cases despite the lower population. 
  • On the other hand, the number of Chikungunya cases has increased in Kerala in 2021 as per provisional numbers. The trend in Telangana is in contrast with a huge reduction in cases in both 2020 & 2021. 

Japanese Encephalitis

In 2020, 729 cases of Japanese Encephalitis (JE) were reported in the country compared to 2545 cases in 2019. The fatality rate due to JE is higher compared to the other VBDs. 

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  • Assam usually reports the greatest number of cases. In 2019, 642 cases with 161 deaths were reported from Assam. Even in 2020, 320 cases with 51 deaths were reported from Assam.
  • Uttar Pradesh reported the second-highest number of cases relating to JE. 
  • Tamil Nadu and Odisha are the other states which have a higher prevalence of JE. However, the number of cases reported in Odisha over the last two years is negligible. 

Kala Azar

As per the data provided in Rajya Sabha, Kala Azar was reported in 6 states of the country – Bihar, Jharkhand, West Bengal, Uttar Pradesh, Sikkim & Kerala. There is an overall declining trend in the number of cases. In 2018, there were around 4.5 thousand cases, which reduced to 3.2 thousand cases in 2019. It reduced further to 2.05 thousand in 2020. As of October 2021, a total of 1152 cases of Kala Azar were reported across the country. 

Of these, Bihar accounts for the most cases. During 2018 & 2019, the state accounted for about 78% of all the cases.  In the ensuing two years, this number is about 72%. 

Lymphatic Filariasis 

In 2018, 12.97 lakh cases of Lymphatic Filariasis (LF) were reported in India. Of these, around 9.03 lakhs were categorized as “Lymphoedema” and the rest as “Hydrocele”. The total number of cases has decreased in 2019 & 2020. In 2019, 6.54 lakh cases were reported, while as per the provisional numbers, there were 6.43 lakh cases in 2020. Bihar, UP, Odisha, West Bengal account for the most cases of Lymphatic Filariasis.

Fall in the incidence of Vector-Borne diseases in 2020 could be due to COVID-19

The common trend across most of the Vector-Borne diseases (VBD) is a fall in the numbers during 2020. The COVID-19 related movement restrictions in 2020 could have played a major role as the number of cases has again increased for multiple diseases in 2021. 

As the healthcare system was overwhelmed with COVID-19 in the year 2020, issues with reporting, recording & treatment of VBDs could also have played a role in the lower numbers.

Featured Image: Vector-Borne Diseases

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