El Nino effect: Cases of dengue have increased globally

Increase in temperature and changes in rainfall patterns to blame

By Vibha Varshney
Published: Saturday 23 December 2023
Photo: iStock

There has been a ten-fold increase in dengue cases between the years 2000 and 2019, according to an analysis by the World Health Organization (WHO). The reported cases have gone up from 500,000 to 5.2 million during this period, the WHO said. The actual number of cases would be higher as the infection is asymptomatic in most cases and it is not a notifiable disease in many countries. 

According to the WHO, there is a sharp increase in cases globally after the lull between the pandemic years 2020-2022. In 2019, when the last spike in cases occurred, the disease was reported in 129 countries. In 2023, 80 countries reported over five million cases and more than 5,000 dengue-related deaths. 

The Americas were the worst affected, the WHO said. Between January 1, 2023 and December 11, 2023, a total of 4.1 million suspected dengue cases, including 6,710 severe cases and 2,049 deaths, were reported from 42 countries and territories in the region.

Active outbreaks were reported from 15 countries in the Americas, with Brazil reporting the highest number of cases, followed by Peru and Mexico.

In the Southeast Asia region, 10 out of 11 member states are known to be endemic for dengue virus. In 2023, several countries in the region reported a notable surge in dengue compared to previous years. Bangladesh and Thailand recorded a larger number of cases.

The Africa region was affected by many arboviral diseases, such as yellow fever, dengue, chikungunya, O'nyong nyong, Rift Valley fever and zika. In 2023, 171,991 dengue cases were reported there, including 753 deaths.

In 2023, outbreaks were reported in 15 of the 47 countries in the African region as well. Burkina Faso with 146,878 suspected cases and 688 deaths among suspected cases was the worst affected. 

WHO’s Eastern Mediterranean region first reported dengue cases in 1998. Since then, the virus has spread to nine countries. Pakistan, Saudi Arabia and Oman have reported the highest number of confirmed cases thus far in 2023.   

The European Region was not affected much and earlier cases used to be mainly travel-related. However, since 2010, the disease has established itself in the region. In 2023, cases and outbreaks have been reported in three countries: Italy, France and Spain.

This year, the Western Pacific Region has reported over 500,000 dengue cases and 750 deaths The most affected countries are the Philippines and Vietnam. Among the Pacific Island countries, Fiji is the worst affected. 

In 2023, the upsurge can be linked to the changing distribution of the vectors (chiefly Aedes aegypti and Aedes albopictus); increase in temperature and changes in rainfall patterns due to the El Nino climate phenomenon; fragile health systems after the pandemic, political and financial instabilities in countries; and high population movements. 

There is an urgent need to increase advocacy and resource mobilisation, the WHO said. A Global Joint Incident Management Support Team has been established involving the WHO Health Emergencies Programme (Response and Preparedness departments) and technical expertise from the neglected tropical disease department to support the response to outbreaks. 

Dengue transmission is cyclic and large outbreaks occur every 3-4 years. Four serotypes of the virus (DENV-1, DENV-2, DENV-3, DENV-4) are present. There is no specific treatment for dengue, but severe cases and mortality can be prevented with timely diagnosis and appropriate clinical management.  

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