Dengue, Chikungunya, and Zika Virus Incidence in Mexico Likely Higher Than Previously Thought

By Marilynn Larkin

December 09, 2021

NEW YORK (Reuters Health) - More accurate testing reveals that the incidence of dengue (DENV), chikungunya (CHIKV) and zika (ZIKAV) viruses in endemic areas of Mexico is likely higher than previously reported, a cross-sectional study shows.

Dr. Jose Esteban Munoz-Medina of the Mexican Institute of Social Security in Mexico City and colleagues note in PLOS Neglected Tropical Diseases that CHIKV and ZIKAV were first detected in Mexico in 2014 and 2015, respectively. However, diagnostic techniques used by the country's National Network of Public Health Laboratories focused solely on DENV until 2017. Prior to implementation of multiplex RT-qPCR testing, the true incidence of these three arboviruses, as well as the incidence of coinfections, was unknown.

Therefore, the team conducted a cross-sectional study of 1,038 serum samples (patients' mean age, 33; 38%, men) to confirm DENV, CHIKV, and ZIKAV diagnoses during the first three years of co-circulation of these arboviruses. The multiplex test can identify any of the three viruses in a single reaction.

The team found 243.8% more cases of arbovirus than originally reported, including coinfections (4.9% of positive samples), suggesting underestimation of the incidence of the three viruses. However, significantly less DENV was observed than in previous years, and the high incidence rates of CHIKV and ZIKAV coincided with periods of dengue decline.

Analysis of the endemic channel showed that DENV cases rose again after CHKV and ZIKAV circulation decreased. Specifically, the month of October was most affected in terms of DENV incidence by the introduction of CHIKV and ZIKV. For example, when graphing the estimated data for 2018, the line exceeded the alarm threshold in October, reaching the epidemic area; this demonstrated a recovery in the number of DENV cases compared to the years of co-circulation with CHIKV and ZIKV.

The authors conclude, "The results obtained in this study show for the first time the real impact on the detected incidence of dengue after the introduction of CHIKV and ZIKV in Mexico, the degree of underestimation of these arboviruses in the country, as well as the co-infections between these viruses, whose importance - clinical and epidemiological - are still unknown."

Dr. Munoz-Medina did not respond to requests for a comment, but two US-based infectious diseases specialists commented on the study in separate emails to Reuters Health.

Dr. Daniel Caplivski, Director, Travel Medicine Program at Mount Sinai School of Medicine in New York City, said, "The findings are interesting in that they suggest that during outbreaks of new emerging viruses (like CHIKV and ZIKAV), there is a decline in virus infections from viruses that are more endemic (such as DENV) This may be due to the changing epidemiology when a novel pathogen is introduced, since so many people in the population are susceptible to infection early in the course of an outbreak."

"Co-infection appears to be relatively rare," he noted. "The findings confirm that it is very difficult to distinguish among these infections on clinical grounds alone. Molecular testing, when available, is much more accurate."

"We should expect more emerging pathogens in different countries over the next few decades, given recent trends," he said. "Having access to multiplex PCR for diagnostic testing will be important in many different settings where novel pathogens may be detected."

Dr. Robert Quigley, Senior Vice President and Global Medical Director of International SOS, headquartered in London, UK, said, "The study reminds the scientific community of the fact that the ecosystem comprised of the host, the vector, and the virus are constantly adapting to survive - hence, the need for continuous epidemiologic surveillance in any region burdened with endemic diseases to ensure a 'balance' is maintained."

"When new virus(es) are introduced into any community," he said, "the diagnosis of the existing and prevalent endemic virus may be temporarily decreased, but once herd immunity is achieved against the new (introduced) virus(es), more likely than not the historic virus will reappear - particularly if it is one like DENV, where an infection does not confer protection against re-infection - until there is a threshold in the community of individuals who were spared infection with the new virus(es)."

"Furthermore," he added, "since coinfections can occur, clinicians should conduct their diagnostic testing accordingly, to ensure their working diagnoses are complete and appropriate treatment can be implemented."

SOURCE: PLOS Neglected Tropical Diseases, online December 2, 2021