Several global trends have significantly increased the risks associated with the emergence and spread of infectious diseases. Urbanization and population growth have transformed our cities into densely populated hubs where diseases can easily spread. Moreover, advancements in transportation have made global travel faster and more accessible than ever before, reducing the time it takes to circumnavigate the globe from months to just hours. This rapid movement of people means that viruses can potentially travel across continents within the incubation period of an infection before symptoms even manifest.
The SARS pandemic of 2002–2003 serves as a stark example of how quickly a new virus can spread globally. Originating in China, SARS-CoV spread to more than two dozen countries within a matter of months, highlighting the interconnectedness of our modern world and the challenges it poses for disease control and prevention.
In addition to human activities, environmental changes driven by agriculture and urban development play a crucial role in disease emergence. The conversion of natural habitats for agriculture or infrastructure projects creates new ecological niches that can harbour disease vectors and reservoirs. For instance, urban yellow fever likely originated when humans entered jungle areas where the virus was maintained in a cycle between monkeys and mosquitoes. The introduction of infected individuals back into urban centres facilitated the virus's adaptation to a new cycle involving mosquitoes like Aedes aegypti, which thrive in urban environments and preferentially feed on humans.
Furthermore, the intensification of agribusiness has led to the concentration of large numbers of livestock or crops in confined spaces. This practice increases the risk of rapid disease transmission among closely packed animals or plants, creating conditions ripe for the emergence of new pathogens or the spread of existing ones.
International trade in plants and animals has also contributed to the spread of diseases across borders. The 2003 outbreak of monkeypox in the United States, for example, was traced back to the importation of Gambian giant rats from Africa as exotic pets. The virus spread from these animals to domestic pets and then to humans, causing public health concerns due to its similarity to smallpox.
These interconnected factors underscore the urgent need for global cooperation and proactive measures to monitor, prevent, and respond to emerging infectious diseases. As our world becomes increasingly interconnected and urbanized, understanding and mitigating the risks posed by infectious diseases have become critical global health priorities.
In the mid-1800s, rabbits brought from Europe to Australia for sport quickly multiplied without natural predators, threatening grasslands and crops in southern Australia. To control their numbers, the myxomatosis virus was introduced in 1950, causing a devastating outbreak among the rabbit population due to its high lethality. Over time, the virus evolved, with less deadly strains becoming more common as rabbits developed genetic resistance. This natural selection favoured moderately harmful strains because milder ones struggled to spread, while highly lethal ones killed rabbits too quickly to transmit effectively.
This situation demonstrates the complexities of using viruses for population control and raises concerns about unintended consequences. Introducing viruses, even for beneficial purposes like managing wildlife, can disrupt ecosystems and pose biosecurity risks. Such considerations are crucial in both wildlife management and assessing the potential risks associated with intentional virus introductions, which could also serve as models for bioterrorism.
Significant progress has been made in the field of xenotransplantation, particularly in using genetically modified pigs as organ donors to address the shortage of human organs for transplantation. Research has focused on various areas such as pancreatic islets, neuronal cells, corneas, and vascularized organs like kidneys and hearts. However, a critical concern arises regarding the potential transmission of known or unknown latent or persistent viruses from donor organs to transplant recipients. This is especially pertinent because transplant recipients undergo immunosuppression to prevent rejection of the transplanted organ, which could make them more vulnerable to infections from viruses originating from the donor species.
In the worst-case scenario, this situation could facilitate the transmission of a foreign virus across the species barrier, allowing it to establish itself as a new human virus. Such a virus could potentially spread from the graft recipient to others, posing significant public health risks. Therefore, while xenotransplantation offers promising solutions to organ shortages, careful consideration and ongoing research are essential to mitigate the risks associated with viral transmission and ensure the safety of transplant recipients and the broader community.
