In March this year, an article published in the Lancet raised concerns that patients testing positive for dengue were later confirmed to have COVID-19. It describes two patients in Singapore with false-positive results from rapid serological testing for dengue who were later confirmed to be infected with SARS-CoV-2, the virus that causes COVID-19. Over the intervening months, other research has shown an intriguing, and also potentially crucial, link between the two seemingly unrelated viruses.
The first of two pieces of research we look at here examines what happened when researchers tested thirteen serum samples containing dengue antibodies for COVID-19. The second examines how dengue influenced the COVID-19 pandemic in Brazil.
What’s most interesting is the conclusions drawn by the researchers on each of the studies.
Dengue and COVID-19 false-positives confirmed
Noting that early symptoms of COVID-19 can be mistaken for dengue, researchers in India were concerned when both dengue and COVID-19 infections had started to rise simultaneously. Dengue numbers were rising as they do every year when the monsoon season hits. COVID-19 numbers were rising as the pandemic spread across the globe.
Worried that dengue antibodies might cross-react with COVID-19 rapid tests, the researchers tested thirteen serum samples for SARS-CoV-2. Of those thirteen samples, five showed a false-positive when tested for SARS-CoV-2 in two different rapid test kits. More importantly, the serum samples were dated 2017, long before the emergence of the COVID-19 epidemic.
So, in dengue-endemic countries, rapid testing kits may misdiagnose dengue patients as having COVID-19. And may misdiagnose COVID-19 patients as having dengue. The researchers concluded:
“It appears that both these viruses have some antigenic similarity that is resulting in the observed cross-reactivity.”
Potential cross-reactivity between dengue and SARS-CoV-2
The story gets even more intriguing when you examine a recent study exploring how dengue influenced the COVID-19 pandemic in Brazil this year. Our second study used mathematical modelling to understand what was behind the uneven geographic spread of COVID-19 cases and deaths in Brazil.
As COVID-19 spread across the country, researchers chanced about a link between the geographic distribution of dengue and COVID-19. Dengue had infected more than 3.5 million Brazilians between January 2019 and July 2020.
The researchers compared each of the country’s states. They looked at what fraction of the population had contracted dengue fever in 2019-2020 and the number of COVID-19 infections. They found that states in which a large proportion of the population had contracted dengue fever in 2019-2020 reported lower COVID-19 cases, infection rates and deaths.
When they looked for a similar link between SARS-CoV-2 and the chikungunya virus, they drew a blank. But when they looked for that link between COVID-19 and dengue in a sample of countries around Asia and Latin America, as well as in islands in the Pacific and Indian Oceans, it was clearly evident.
The researchers raised the possibility of ‘immunological cross-reactivity’ between dengue and SARS-CoV-2, concluding:
“Dengue infection or immunization with an efficacious and safe dengue vaccine could produce some level of immunological protection for SARS-CoV-2 before a vaccine for SARS-CoV-2 becomes available.”
We are still at the start of our journey to advancing our knowledge on the link between dengue and COVID-19. There’s a distinct possibility that uncovering potential new ways to fight either of these seemingly unrelated viruses might unlock the answer to combatting them both. But we have a lot more to learn.