influenza outbreak
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A recent study explored the seasonal outbreaks of infectious diseases. Similar to the influenza outbreak, many other infectious diseases have seasonal features.

There are many examples, including the common cold, of a seasonal transmission of infectious diseases. Polio, in the past, would peak in the summer and gonorrhea outbreaks tend to occur in the warmer months. Chickenpox typically peaks in the springtime. These are examples of acute infections of common public interest. Other chronic infections like hepatitis B and HIV-AIDS may also have seasonal drivers.

Four seasonal drivers influence disease transmission

There are four seasonal drivers that influence the transmission of several infectious diseases.

  1. Environmental factors, such as temperature and rainfall, influence the spread of many tropical infectious diseases like cholera.
  2. Host behaviour, such as the assembling of children at the beginning of the school year, increases the transmission of the measles, for example.
  3. Host phenology including activities of hibernation and reproduction is also a seasonal driver of infectious diseases.
  4. Ecological factors like the interactions between different parasites impact when and if an epidemic will occur.

The scientific community has ignored the seasonality of many infectious diseases

These examples of infectious diseases following seasonality are well documented. Nevertheless, the scientific community has largely ignored the seasonality of the majority of infectious diseases. Dr. Micaela Martinez, a researcher from the department of environmental health sciences at Columbia University in New York, United States, rigorously explored the idea of an epidemic calendar.

Using the examples of the flu season and the gonorrhea season, Dr. Martinez compiled a list of over 60 infectious diseases and researched their seasonal drivers. The results of this analysis were published in PLOS Pathogens.

Dr. Martinez compiled a list of 69 infectious diseases. By searching key terms in Google Scholar, Dr. Martinez was able to associate each chronic and acute disease with a seasonal driver. Among the four broad seasonal drivers of infectious diseases, eight specific seasonal drivers were identified in the literature.

For example, the influenza outbreak is influenced by seasonal climate whereas Ebola transmission coincides with the seasonality in animal-human contact. Yaws, an infectious disease caused by the bacterium Treponema pertenue, has a relatively constant transmission throughout the year but there is a distinct increase in relapse rates particularly during the wet seasons. This is an example of a seasonality in relapse rates of this infectious disease. Bacterial pneumonia follows the transmission of the influenza outbreak. This virus-bacteria interaction might be implicated in the transmission of bacterial pneumonia.

Seasonal influence on infectious diseases is a complex relationship

The association of infectious diseases and their seasonal drivers is a complex relationship. Each infectious disease may have multiple drivers of their transmission. The purpose of this study is to stimulate further interest in the seasonality of infectious diseases. Many different organizational levels of science need to collaborate to map out the epidemic calendar. By identifying the mechanisms of the seasonality of infectious diseases, scientists and clinicians would better control transmission.

In conclusion, the influenza outbreak is not the only infectious disease that has a seasonal outbreak. Over 60 different infectious diseases have been identified with a seasonal driver. By mapping out the seasonality of these diseases with further research, disease control interventions can be optimized to prevent seasonal outbreaks.

Written by Jessica Caporuscio, PharmD

References:

  1. Martinez ME. The calendar of epidemics: Seasonal cycles of infectious diseases. PLoS Pathog. 2018.
  2. EurekAlert!Mark your calendar: All infectious diseases are seasonal [Press Release]. American Association for the Advancement of Science (AAAS). 2018 nov. https://www.eurekalert.org/pub_releases/2018-11/cums-myc110118.php
  3. WHO. Yaws: A forgotten disease. http://www.who.int/neglected_diseases/diseases/yaws/en/
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