Every Infection Has Its Own Season

Every infection has its own season

Seasonal illness isn't just the flu. This quality is found in gonorrhea, measles and even hepatitis B.

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Many are aware of the seasonal nature of flu outbreaks. However, Micaela Martinez of the Columbia Mailman School of Public Health in the US recalls in her article that many infectious diseases are seasonal. Her article was published in PLOS Pathogens magazine.

In her research, Dr. Martinez used information from the World Health Organization (WHO), data from the US Centers for Disease Control and Prevention (CDC), and publications in medical journals. Based on the data obtained, she created a calendar of epidemics of 69 infectious diseases, ranging from the most common infections to rare tropical diseases. This year, for example, there will be outbreaks of influenza in winter, chickenpox in spring, and gonorrhea and poliomyelitis in summer.

Dr. Martinez found that seasonality occurs not only in acute infectious diseases like the flu, but also in chronic infections such as hepatitis B, which, depending on the location, flare up more frequently at certain times of the year. Preliminary studies have also shown that even with the spread of HIV-AIDS, there is a seasonal element that is believed to be influenced by seasonal factors of malnutrition associated with crop seasonality.

The article describes four main factors of seasonality of infectious diseases. For example, environmental factors such as temperature and humidity regulate seasonal outbreaks of influenza, and the seasonality of Zika virus disease is related to the multiplication of its vectors, the mosquitoes.

Such a seasonal factor as the school year is associated with the spread of measles, since children come into contact with each other at a certain period. Environmental factors, which include seasonal algae reproduction, play a role in the occurrence of cholera outbreaks. Seasonal biological rhythms, similar to those that regulate migration and hibernation in animals, may also play a role in the spread of diseases such as poliomyelitis, although more research is needed to confirm this.

“Seasonality is a universal feature of infectious diseases, although the scientific community largely ignores this factor when considering most infections. Much work remains to be done to understand how the forces that cause seasonal illness work and then to understand how to use seasonality to design interventions to prevent outbreaks and treat chronic infections,”Martinez says.

Identifying the causes of seasonal outbreaks is not always easy, but it can be beneficial. For example, the bacteria that cause cholera are spread among humans through the alimentary (fecal-oral) mechanism of transmission. These bacteria can live long in water if microscopic algae are present. Doctors may try to prevent transmission of cholera from infected people and / or fight directly against bacteria in bodies of water with such algae. However, different cholera control activities will differ depending on the season.