COVID-19 and dengue: a deadly duo

Introduction

Since December 2019, when a cluster of atypical pneumonia infections were found in Wuhan, China, the pandemic unleashed by the SARS-CoV2 (COVID-19) virus has now spread across the globe, with more than 5 million confirmed cases and over 360,000 fatalities. The pandemic has reached the tropical shores of South Asia, Africa and South America slightly later than Europe and East Asia. While that has allowed some time to prepare, it also means that the pandemic potentially coincides with another epidemic already in the region, dengue.

Dengue fever is an acute febrile illness transmitted by the Aedes mosquito. It is believed that almost half the world population is at risk, with those in tropical and subtropical climates having the highest risk. A total of 390 million dengue infections are estimated annually, but only 67–136 million will have clinical manifestations. ¹ The overall incidence of dengue seems to have increased 30–50-fold over the past 50 years. ²

With increasing incidence of dengue worldwide, the arrival of COVID-19 may signal disaster.

Two epidemics in one

Dengue has been proliferating in Latin America and South-East Asia, ³ with an increasing risk that healthcare systems become overwhelmed threatening healthcare ecosystems that are already fragile. To complicate things further, there are similarities in the initial presentation of patients with COVID-19⁴ and dengue, ⁵ namely fever, myalgia and headache, associated with leukopenia, thrombocytopenia and abnormal liver function tests.^4,5 Therefore, they can be fairly difficult to distinguish early on. Even cutaneous manifestations of severe dengue ⁵ are not necessarily enough to distinguish early between the two, as COVID-19 may present with cutaneous manifestation in three different forms: erythematous rash; urticaria; and chickenpox-like lesions. ⁶

A case was reported of a patient with febrile illness and petechiae in Thailand, ⁷ a very common presentation for dengue. Moreover, the patient also had thrombocytopenia, also a very common finding in dengue. ⁵ The patient was to later develop respiratory symptoms, upon which reverse-transcription polymerase chain reaction (RT-PCR) was done which confirmed COVID-19 infection.

Further complications have been raised with the possibility that SARS-CoV2 infection may give false-positive results on dengue rapid testing. Two cases of febrile patients in Singapore were reported to be positive for dengue and later confirmed to have COVID-19 as well. ⁸ Both times, further RT-PCR for dengue virus was later confirmed to be negative. The authors deemed the dengue results to be false positives and that the patients actually had COVID-19.

A case of COVID-19 transmission to a healthcare worker from a presumed dengue patient has also been reported in Thailand. ⁹ The dengue patient was not managed with any respiratory precautions. This patient, initially managed as dengue, was later given an additional diagnosis of COVID-19, thus being a case of co-infection rather than having a false-positive dengue.

Whether false-positive dengue or a co-infection with COVID-19, the situation is complicated by the similarity of both diseases.

However, there are some key differences that could help differentiate the initial presentations of each. COVID-19 is primarily a respiratory infection, and thus will present with a cough in > 75%, with up to 25% having a productive cough, ⁴ something very unlikely in a patient with dengue. ⁵ Moreover, sore throat and nasal symptoms, described in COVID-19, ⁴ have not been described in dengue. ⁵ Moreover, dengue may present with monocytosis in addition to lymphopenia and thrombocytopenia. ⁵ This finding has not been described in COVID-19. ⁴

Risk of an overburdened healthcare system

Simultaneous epidemics of dengue and COVID-19, notably in Latin America,^10,11 as well as the possibility of co-infection, add to the already heavy burden on healthcare services in Brazil ¹² and Ecuador. ¹³

While some have suggested that COVID-19 infection and transmission may be slower in dengue-endemic regions of the world, ¹⁴ there is little evidence to back up that assertion, especially as COVID-19 has since accelerated in both South-East Asia and South America,^12,13,15 regions known for their prevalence of dengue.

Moreover, some regions in the world, such as South Asia, are yet to reach their peak dengue season this year. Bangladesh recorded more than 100,000 cases of Dengue alone in 2019, ¹⁶ being described as the worst dengue epidemic in the country. This was also reported to likely be an underestimate. Moreover, there was suggestion of significant risk of co-infection with influenza and enteric fever between April and November, the expected time for the peak of COVID-19 in the country as well. ¹⁷

Conclusion

While the world struggles to grapple with the burden of the COVID-19 pandemic, areas with endemic dengue fever are facing the prospect of a dual pandemic that could overwhelm healthcare services. Good epidemiological and contact history-taking combined with the awareness of false-positive dengue serology and the possibility of co-infections are key tools for frontline physicians faced with what seems to be an insurmountable challenge. Rapid, reliable point-of-care testing for COVID-19 needs to be made available, with validation being done within each country for help in isolating such patients.