By Barry C. Fox, M.D., University of Wisconsin
Let’s look at the various infectious diseases we know and try to figure out which ones would be the likely candidates to cause a pandemic. There are four categories of germs that we must consider: bacteria, viruses, insect-borne diseases, and tick-borne diseases. Keeping these diseases in mind, let’s talk about elements necessary for a pandemic to spread.
There are some crucial elements that are ideal for the creation of a pandemic germ. First is human-to-human transmission. Secondly, the potential to mutate rapidly. Thirdly, there is no known treatment or vaccine. Fourth, the capacity to spread rapidly, especially in crowded conditions. Fifth, a high—but not too high—mortality rate. Sixth, a short incubation period, so the disease has likely been spread to others before the person is sick. Seven, resistance to multiple antibiotics or antiviral medications.
What Diseases to Exclude?
With these clues in mind, can we exclude any types of diseases? Let’s look at tick-borne diseases. Since they are not transmitted from human to human, and there are medicinal treatments for most of them, we’re not as concerned about these becoming our pandemic culprit. At this point, we’ll rule out diseases in this category.
We’re also going to exclude insect-borne diseases, as a specific vector has to be present in the geographic area since specific insects transmit specific diseases. For example, malaria requires the Anopheles mosquito for transmission, and these mosquitos are found mostly in India and Africa. Also, these illnesses result from chance occurrences of insects, and also, we have the means to control the deadly vectors of transmission. Finally, for the most part, these diseases have not demonstrated the capacity to be transmittable between humans.
Learn more about tick-borne diseases.
Bacterial and Viral Pandemics
Let’s look at historical lessons from pandemics of the past. There have been seven cholera pandemics till now. The first cholera pandemic was documented in 1816 in Bengal, India, and the latest one started in 1962 in Indonesia, and has been ongoing for 50 years.
There have been several pandemics attributable to plague. It is a vector-borne disease spread by the bite of fleas that fed on rodents infected with Yersinia Pestis. Sporadic cases still occur in the United States, and nearly 100 cases erupted in Madagascar in 2014. There have been four influenza pandemics in the last century, all the result of reassorted viruses.
Better Disease Control?
Cholera, plague, and influenza have been wreaking havoc for many years. What factors have changed since the 19th and 20th centuries that might influence our pandemic possibilities? Are these older pandemic germs now under control?
We do have better control of diseases at least in some areas. We have new vaccines, better protective equipment like gloves and masks, and improved funding from global sources, global surveillance systems that coordinate responses.
This is a transcript from the video series An Introduction to Infectious Diseases. Watch it now, on Wondrium.
Emerging Diseases and Environment
There are also new and emerging diseases. Since the 1990s, we have seen AIDS, SARS, MERS, MRSA, swine flu and drug-resistant forms of tuberculosis. We’ve also seen old diseases, like cholera and dengue, re-emerge.
What about environmental influences? We keep destroying animal habitats at increasing rates, and entering places where man has not lived before. For example, in the last 40 years, 20 percent of the Amazon rain forest has been destroyed. This makes contact with species in those forests more likely and could bring more zoonotic diseases with pandemic potential.
Even climate change affects infectious disease rates, since vectors like mosquitos and ticks, bacteria and viruses are affected by temperature changes and the amount of precipitation. Some scientists believe cholera may become more common as the bacteria grows more rapidly in warmer waters. Others believe that mosquito-borne diseases will be more prevalent as the warming extends their life cycles.
Learn more about the easily cured childhood illnesses of the 50s.
The Hypothesis
Each regional area has its own issues that may contribute to a pandemic. But due to environmental factors, scientists seem to favor East Asia or Southeast Asia. This hypothesis is based on the extensive contact with both wild animals sold for their meat and farm animals, as part of huge, crowded farming operations. In addition, these are densely populated areas in which a pathogen could spread rapidly.
Common Questions about the Conditions for a Pandemic
Some parameters of infectiousness that are necessary for a pandemic are the capacity to spread rapidly, especially in crowded conditions; a high—but not too high—mortality rate; and a short incubation period, so the disease has likely been spread to others before the person is sick.
We do have better control of diseases at least in some areas. We have new vaccines, better protective equipment like gloves and masks, and improved funding from global sources, global surveillance systems that coordinate responses.
Climate change affects infectious disease rates, since vectors like mosquitos and ticks, bacteria and viruses are affected by temperature changes and the amount of precipitation. Some scientists believe cholera may become more common as the bacteria grows more rapidly in warmer waters. Others believe that mosquito-borne diseases will be more prevalent as the warming extends their life cycles.
We keep destroying animal habitats at increasing rates, and entering places where man has not lived before, such as rainforests. This makes contact with species in those forests more likely and could bring more zoonotic diseases with pandemic potential.
