Since its introduction in 2014, chikungunya has caused more than one million infections in Brazil through multiple epidemic waves.
Yet despite its impact, it is often overlooked for other mosquito-borne infectious diseases, such as dengue and Zika, leading to its true case numbers and severity being underestimated.
In a recent study published in The Lancet Microbe, researchers in the UK, Brazil and the United States combined genomic data on the virus with epidemiological models to gain new insights into the ongoing chikungunya epidemic in Brazil.
Q - What is chikungunya and how does it spread?
Nuno Faria - Chikungunya is an infectious disease found in Africa and Asia, including the Indian and Pacific Oceans. Over the last decade it has also spread to the Americas, including South and Central America and the Caribbean.
It’s caused by a virus which is transmitted to humans by two types of mosquito – Aedes aegypti and to a lesser extent, Aedes albopictus.
Over the past 20 years, there have been more than 10 million reported cases of chikungunya in more than 125 countries or territories, including in Brazil.
Infections usually present as severe joint pain and fever, as well as headaches, muscle pain and skin rash. As symptoms so closely resemble dengue and Zika (also spread by the same mosquitoes), it can often be misdiagnosed and so the true case numbers and deaths may be underestimated.
Q - Which countries or regions are most affected by the disease?
NF – The disease regularly occurs in Arica and is endemic in Asia where it causes recurrent and occasionally large epidemics particularly in the Indian Ocean and Southeast Asia. Over the last 20 years, chikungunya re-emerged and caused large outbreaks in Kenya, Indian Ocean islands and South and North America.
In 2013, the virus was introduced from Asia to the Caribbean and from there to South and North America. In 2014, it was introduced from Angola to Brazil. Outbreaks have become more frequent and widespread.
In Europe, the virus has also caused small outbreaks in Italy and France. The increased geographic range of the disease is partly down to how the virus is adapting to transmission by the Aedes albopictus mosquitoes in more temperate areas.
Brazil has seen the highest number of cases of chikungunya in the Americas with more than 1.2 million cases over the past decade. Since 2018, Brazil reported 85% of the nearly 1 million chikungunya notified cases in Latin America, according to the Pan American Health Organization.
Q – How can it be prevented or treated?
NF - Although there is an increasing interest in the development of effective chikungunya vaccines, there is currently no approved vaccine or specific treatment for this debilitating disease with major public health impact.
The deployment of Wolbachia has shown promising results in the reduction of chikungunya incidence in one site in Brazil. But more generally, preventing bites from infected mosquitoes currently provides the best protection for individuals.
For those with an infection, doctors may recommend paracetamol for pain relief and to reduce fever until the risk of dengue infection is ruled out. This is because non-steroidal anti-inflammatory drugs (NSAIDs), like ibuprofen, can increase the risk of bleeding in dengue.
Q – What does your work show about chikungunya in Brazil?
NF - Our recent analysis investigated how chikungunya has spread in Brazil since its introduction almost 10 years ago.
Within the Americas, chikungunya epidemiology in Brazil is unique as two specific lineages, the Asian and the East-Central-South-African (ECSA) lineage, have co-circulated in the country.
We find that between 2013 to 2022 there have been seven epidemic waves of chikungunya across Brazil, affecting almost 60% of municipalities. Ceará State in the northeast of the country has been the most affected, with 77,418 cases during the three largest epidemic waves in 2016, 2017, and 2022.
We find that the most recent outbreaks in Brazil tend to occur in cities that had not been affected by the virus in previous epidemic waves. Overall, our studies show that the continued transmission of chikungunya in Brazil can be explained by diverse spread of chikungunya virus during the first waves. It is expected that chikungunya will continue to cause outbreaks in Brazil and elsewhere, particularly in populations that have not yet been exposed to the virus.
We have gained some interesting insights from sequencing the genomes of isolated chikungunya samples. We find that the chikungunya resurgence in 2022 in Ceará State, was associated with the introduction of a novel ECSA strain, introduced to the area in mid-to-late 2021 from other Brazilian states.
We also estimate a case-fatality ratio for chikungunya of 1.3 deaths per 1,000 confirmed cases, which is higher than other mosquito-borne diseases in tropical countries, such as dengue and Zika.
Q – Have any trends emerged about who is most affected?
NF - We’re seeing that overall, women are more likely to contract chikungunya than men in Brazil, and interestingly, that outbreaks of the disease are not necessarily related to high density of mosquito populations in those regions.
Chikungunya infection is believed to provide life-long immune protection against subsequent infections, even with other lineages. There is now some degree of population immunity in Brazil, especially in municipalities most affected by previous chikungunya epidemic waves, with local populations having some level of protection against the infection.
Q - How could these findings help to prevent or treat chikungunya in future?
NF - Unless we see interventions put in place – such as mosquito control measures, or the development of vaccines and antivirals – we can expect further waves of chikungunya outbreaks in Brazil, causing thousands of cases and deaths.
We hope that our work will be able to help inform public health agencies to anticipate and even prevent future chikungunya outbreaks.
Spatial-temporal dynamics and recurrence of chikungunya virus in Brazil: an epidemiological study’ by William de Souza et al, is published in The Lancet Microbe. DOI: https://doi.org/10.1016/S2666-5247(23)00033-2
Dr Nuno Faria is Reader in Viral Evolution within the MRC Centre for Global Infectious Disease Analysis at Imperial College London. His work focuses on rapidly evolving viruses that circulate in humans and animals, such as SARS-CoV-2, yellow fever, chikungunya, Zika and dengue. He also coordinates the Brazil-UK Centre for Arbovirus Discovery, Diagnostics, Genomics and Epidemiology (CADDE) and he is part of the Technical Advisory Group for the WHO Global Arbovirus Initiative.
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