Zoonotic spillover epidemics increasing at exponential rate, study finds

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All four animal-to-human (zoonotic) infections are increasing at an “exponential rate” in a general pattern of increasingly larger and more frequent ‘spillover’ epidemics, according to an analysis of 60 years of published historical epidemiological data. Open Access Journal BMJ Global Health.

Based on current trends, these 4 types of viral pathogens will collectively kill 12 times more people in 2050 than in 2020, the researchers warn.

Changes in climate and land use are predicted to drive the frequency of spillover events, which are facilitated by population density and connectivity, the researchers explain. Animal-to-human transmission has caused most modern epidemics.

But the implications for future global health are difficult to predict given the limited historical data on the annual frequency and intensity of zoonotic spillovers over time.

To achieve this, they developed their own extensive epidemiological database to look for trends in spillover events that could shed light on expected future patterns.

This database draws on a wide range of official sources. It covers epidemics reported by the World Health Organization in the form of Disease Outbreak News Reports (WHO DON); An outbreak caused by a viral pathogen that has killed 50 or more people; and significant historical outbreaks, such as the 1918 and 1957 flu pandemics.

Researchers have focused on filoviruses (Ebola virus, Marburg virus), SARS coronavirus 1, Nipah virus, and Machupo virus, which causes Bolivian hemorrhagic fever, because they may pose significant risks to public health and economic or political stability.

They looked at more than 3,150 outbreaks and epidemics between 1963 and 2019 to analyze trends over time in the number of outbreaks and associated deaths caused by these viral pathogens.

They identified a total of 75 spillover events in 24 countries during this period. This resulted in a total of 17,232 deaths, of which 15,771 in 40 outbreaks – mostly in Africa – were caused by filovirus.

Their analysis, which excluded the COVID-19 pandemic, showed that each year between 1963 and 2019, the number of spillover cases and reported deaths attributable to these four groups of viruses increased by about 5% and 9%, respectively.

“If this annual growth rate continues, we would expect the analyzed pathogens to cause four times the number of spillover events and 12 times more deaths in 2050 than in 2020,” they estimate.

These figures are likely to be an underestimate, they suggest, due to the strict inclusion criteria for pathogens in the analysis, which effectively negated the effect of advances in surveillance and detection during the study period; and excluding the ongoing COVID-19 pandemic.

“Our evaluation of the historical evidence suggests that recent series of epidemics driven by zoonotic spillovers are not aberrations or random clusters, but follow a multi-decade trend in which spillover-driven epidemics have become larger and more frequent,” they wrote..

“The final package of actions to support global prevention, preparedness and resilience is not yet clear. But what is clear from historical trends is that urgent action is needed to address a large and growing risk to global health,” they .


Journal Reference:

Meadows, AJ, etc. (2023). Historical trends demonstrate a pattern of increasingly frequent and severe spillover events of high-consequence zoonotic viruses. BMJ Global Health. doi.org/10.1136/bmjgh-2023-012026.

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