Global Health: Reemerging Infectious Diseases

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Reemerging Infectious Diseases

 Figure 1. Biocomplexity drives reemergency (Adapted from wilcox et al)

 Figure 1. Biocomplexity drives reemergency (Adapted from wilcox et al)

Reemerging infectious disease are diseases that have recently increased in incidence, in geographic range, or in host range. Many reemerging infectious diseases are also classified as neglected tropical diseases (NTDs). Diseases that are considered both reemerging infectious diseases and NTDs pose a dual threat. These "dual threat" diseases often emerge in areas where they had not previously been endemic. Because they are also NTDs, surveillance and treatment can be difficult.  

Infectious diseases reemerge for many different reasons. Reemergence is usually driven by changes in the complex relationship between ecosystem dynamics and human-natural system behavior, termed biocomplexity (Figure 1). Biocomplexity, most commonly used to describe the reemergence of zoonotic or vector borne infectious diseases, is comprised of complicated dynamics between environmental changes, public health infrastructure, climate, and host and pathogen evolution and adaption. The dynamic and interconnected variables making up biocomplexity lead to regional and global changes that drive the reemergence of infectious disease. We will frame this by the NTDs seen as the hallmarks of this reemergence around the world.

Cholera

Cholera is spread by food or water contaminated with Vibrio cholerae causing the abrupt onset of voluminous diarrhea and vomiting. Cholera's reemergence is one of the most well understood and extensively studied of all infectious diseases. Peru's cholera epidemic in 1991 launched a scientific inquiry into why cholera had reemerged into an area where it had not been endemic for over 100 years. Scientists were able to trace the cause of the 1991 epidemic, and subsequent outbreaks in this area, to global weather patterns, aquatic reservoirs, bacteriophages, zooplankton, and other factors contributing to cholera's reemergence. 

Scientists discovered that cholera reemergence coincides with dry, warm weather and zooplankton blooms. Additionally, as climatologists predict a 1.4-5.8°C increase in mean global temperature over the next 100 years we may experience a reemergence of cholera in the US. Neighboring the United States, a strain of V. cholerae, similar but not identical to pandemic strains, has been endemic in the Gulf of Mexico since the 1970s. This strain of cholera is intermittently responsible for infections related to the consumption of raw or undercooked seafood. There is concern among scientists that as global temperatures rise this strain of cholera in the Gulf of Mexico may reemerge causing more than just sporadic infections.

Arboviruses

Aedes Mosquito. The vector responsible for human epidemic arboviruses.

Arboviruses are viruses that are transmitted between arthropods and vertebrates during their life cycle. There are five human epidemic mosquito-borne arboviruses: Yellow Fever, Dengue, West Nile, Chikungunya, and Zika. The epidemiology of the mosquito vector ofis closely linked to the reemergence of epidemic arboviruses. In the past 30 years there has been a reemergence of West Nile, Chikungunya, and Zika in the United States and nearby regions. On a global scale, Dengue is the arbovirus that has been reemerging both at a faster rate and with more virulence. It isnow thought to be endemic in 125 countries world wide. This has led the World Health Organization (WHO) to call Dengue "the most important mosquito-borne viral disease in the world". 

Many factors, such as climate change and globalization have led to the reemergence of arboviruses. Climate change is thought to be a contributing factor to the increase in geographical distribution of the Aedes mosquito. Globalization has allowed for increased mobility of both vector and human populations. The mobility of the human population is thought to be responsible for the recent spread of Chikungunya to the Caribbean.

Chagas Disease

Trypanosoma cruzi on a blood smear.

Chagas disease is caused by the parasite Trypanosoma cruzi most commonly spread by the triatomine bug. Other significantly less common etiologies of infection with Trypanosoma cruzi include blood product transfusion, solid organ transplant, ingestion, and vertical transmission leading to congenital Chagas disease. Acutely, Chagas disease presents with fever, malaise, hepatosplenomegaly, lymphadenopath, and characteristic cutaneous manifestations. Chronically, Chagas disease is known for its cardiac and GI complications. 

Acute presentation of Chagas disease is rare in the United States, however it ranks 7th world-wide for total number of people infected. Reemergence of Chagas disease is thought to be due to deforestation, poor dwelling construction, and, most commonly in the United States, population migration from Central and South America. Because of this, chronic disease or reactivation of Chagas disease due to a new immunocompromised state, is a more common presentation in the United States.

Strategies and Solutions 

Management of reemerging infectious diseases is focused on strategies to decrease vector and pathogen reemergence and improve disease treatment and diagnostics. Increasing surveillance of pathogens and vectors as well as strategies focused around vector control have been shown to help reduce disease reemergence.  Because many reemerging infectious diseases are also NTDs it is also vital to encourage research and development of new vaccines and therapeutics.

Check out more disease-specific cases on our Global Health Site

Post by Grace Lagasse, MD

Peer Review by Whitney Bryant, MD

References

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