In this study, we outline two cases of simultaneous infection with DENV and CHIKV in Brazil, a new finding in a region previously undocumented for such coinfections. Despite the rarity of DENV-CHIKV coinfection discussions, most are from India, where the endemicity for both viruses is high, and a coinfected rate of 9.5% was reported [14, 15,16].
The detection of DENV and CHIKV coinfections in December 2023, ahead of the anticipated epidemic season of April to June 2024, underscores an urgent need for the healthcare system to adapt to this evolving threat. These cases were identified in the Ribeirão Preto region, an area with a significant history of dengue fever outbreaks, with annual confirmed cases reaching between 12,000 and 17,000 in recent years. Interestingly, CHIKV incidents belonging to imported origin have remained relatively low, according to the region's health bulletin, over the past five years (ranging from 0 to 8 cases per year) [11]. However, a notable increase in autochthonous cases was observed towards the end of 2023, November and December, the peak periods. This critical shift in the epidemiological landscape requires vigilant public health responses.
The spread of arboviruses is intricately linked to various factors, mainly climate factors such as rainy periods and extreme heat, which favor the proliferation of Aedes aegypti, the common vector for both DENV and CHIKV. Peculiarly, Aedes aegypti mosquitoes have been extensively studied, revealing that this mosquito species can harbor hosts and vectors for both viruses in vitro settings [16,17]. Lin and colleagues (2023) further demonstrated that simultaneous infection with DENV and Zika virus in Aedes aegypti could intensify viral replication within the mosquito [18]. This enhanced replication capacity, alongside the mosquito's ability to transmit multiple viruses, raises critical questions regarding the potential for human infection resulting from successive exposures to mosquitoes carrying DENV, CHIKV, or both.
Considering the shared transmission vector for DENV and CHIKV, the dynamics of these coinfections among humans justify further investigation to understand the full scope of arbovirus transmission efficacy [19]. This case was detected in the same areas where most CHIKV-confirmed cases have been identified. The discrepancy between the results of serology and RT-PCR is explained. Early recognition and appropriate medical care are essential for a favorable patient outcome, although many clinical symptoms overlap between these viruses.
The approval of the DENV vaccine, QDenga (Takeda, Japan), in March 2023, with the campaign launched in February 2024 focusing on specific age groups and priority regions, represents a significant advancement in dengue prevention. This vaccine is an attenuated virus with an efficacy of 72.7% (López-Medina et al., 2022). However, one of the main critical challenges of managing dengue's four serotypes: DENV-1, DENV-2, DENV-3, and DENV-4; once the infection with one serotype does not provide immunity against the others.
This challenge is exacerbated by the increasing number of autochthonous CHIKV cases in our region. Notably, CHIKV infection is already endemic in many other regions of Brazil, such as the Northeast, leading to coinfections that can complicate the diagnosis and management of patients due to overlapping clinical symptoms. Moreover, numerous questions remain unanswered regarding whether dual infection could result in more severe disease and complications. Additionally, the implementation of discriminatory diagnostics for DENV and CHIKV is currently lacking in Brazil's public healthcare systems.
Our findings reinforce the critical need for comprehensive research into the dynamics of coinfection, immune responses, and the interactions between these viruses, aspects that remain insufficiently understood. There is a clear imperative need for robust surveillance systems, advanced diagnostic tools, effective vector management strategies, and public health education campaigns to mitigate the impact of these arboviral infections. Understanding and addressing the nuances of coinfection will be crucial in formulating effective responses to these public health challenges.