Research: How travelers spread diarrheal diseases

Among the infectious diseases that afflict humans, acute diarrheal diseases caused by the consumption of contaminated food and water are the leading cause of morbidity and mortality worldwide. These illnesses are mainly caused by bacteria, parasites, and viruses; the latter are the most frequent, but less documented.

In Mexico, five to six million cases of acute diarrhea are reported each year. However, 94% of the cases are classified as "ill-defined," without determining the organism causing the disease, so the possible source of infection is reported based on the patient's clinical picture.

The scientific literature has suggested that domestic and international travelers are major contributors to the spread of infectious diseases around the world. Human noroviruses and enteroviruses are two groups of enteric viruses that contribute significantly to cases of acute diarrheal infections worldwide.

The fecal-oral route is how these viruses spread, and most of their virions (genetic material) are shed in feces, which are then released into the environment through sewage.

As part of her academic training as a Master of Science at the Center for Research in Food and Development (CIAD), Roxana Alicia Cázares Olivas set out to study the incidence of enteric viruses in wastewater from bus depots, as this strategy is considered a useful tool in epidemiology since it provides information on the presence of specific pathogens in a given population and is a topic that has been little studied in Mexico.

Under the guidance of research professor Osvaldo López Cuevas, an academic at CIAD's Culiacán Regional Coordination, the student made a project whose goal was to find out if there were enteroviruses and human norovirus genogroups in wastewater from the city of Culiacán, Sinaloa.

As part of the experiment, 16 wastewater samples were collected in the reservoirs of foreign and international buses in that municipality at a weekly frequency during the months of February, March, and April 2022.

The samples were concentrated by precipitation with polyethylene glycol 6000 and sodium chloride, followed by extraction of total RNA and determination of the presence of the viruses by real-time RT-PCR.

The student found, among other things, that of the sixteen wastewater samples she looked at, norovirus GII was found in two of them but enterovirus was not found in any of them.

According to Cázares Olivas, the evidence obtained in the project supports the hypothesis that people who travel carry enteric viruses, which increases the probability of dispersion of diarrheal infections in the populations where they arrive.

Just as we have learned to live in a "new normality" due to the sanitary contingency brought about by the COVID-19 pandemic, we should take preventive measures to avoid contracting diarrheal diseases when traveling by bus, explained the student.

Some of the considerations we can take into account are to maintain good hygiene through hand washing, especially when we touch potentially contaminated surfaces in public spaces.

She concluded that a clear example is the potential transfer of pathogenic microorganisms to handrails and other objects on buses by people carrying them, which leads to the infection of other passengers if sanitary measures are not applied.