With the entertainment industry’s preoccupation with world-devastating viruses in recent decades it’s easy to see how public anxiety has increased regarding apocalyptic scenarios. When it comes to the next world pandemic, the question is when it will happen, not if. Insects and animals represent two prime vectors through which viruses and other pathogens can adapt and change to the point where they pose a danger to humans. What happens during this process though? Is there any way it can be stopped or slowed? How can we minimize the chances of the next world pandemic causing significant harm to human civilization?
Historically, insect and animal vectors have been devastating. The Black Death (now known as the bubonic plague), which killed over 25% of Europe’s population in the 14th century, was caused by the Yersinia pestis bacterium, which gained proximity to humans by infecting fleas, which then infected rats. Thus, rats were an animal vector (and fleas an insect vector) for the pathogen. In a time when garbage disposal and planned sanitation routes did not exist, both rats and fleas were a major problem for densely populated cities. Rats infected by fleas were constantly in close contact with humans, which made controlling a plague outbreak extremely difficult given the high population density and lack of mobility for most citizens.
While animal and insect vectors certainly spread a fair number of pathogens, arthropods represent the bulk of vectors for transmitting diseases to humans. Arthropod vectors include lice, fleas, ticks, mites, mosquitoes, and sand flies. These organisms typically feed on blood at some (or all) stages of their lives. During feeding, the parasite enters the host’s bloodstream and infection is complete. The Oriental rat flea (Xenopsylla cheopsis, the flea responsible for serving as a vector for the Black Death) is one such example. The methods that arthropod vectors use in accessing human blood can vary, but all succeed in transmitting the infection to a new host.
Modern sanitation and garbage disposal methods have helped to drastically reduce the number of opportunities many of these organisms had to feed on humans in the past. Advances in medical technology and biological knowledge have brought understanding of how these pathogens spread and what must be done to reduce risk. Keeping grass, shrubs, and tree branches trimmed can reduce the possibility of ticks climbing into positions for easier access to human hosts. There has also been a marked improvement regarding public education and arthropod vectors: most members of the public (especially in rural areas) know to notify medical professionals if bitten by an unknown insect or animal, which may be serving as a vector for a pathogen. Access to healthcare services soon after a bite from one of these vectors will minimize the chances of long-term health implications.