A report released in December last year has highlighted 37 diseases that have pandemic potential. All of these infections are zoonoses – they infect animals but are able to jump the species barrier and infect animals. Their official title is zoonotic diseases. All 37 diseases would have dire impacts on human health across the globe. The report, run at the University of Edinburgh, was published in the Journal of Emerging Infectious Diseases
Prof Mark Woolhouse, one of the lead authors of the study had this to say:
“Monitoring these infections should be prioritised because relatively minor changes in their ecology could lead to major changes in the threat they pose to public health.”
The CDC say in their abstract of the study:
Many new and emerging RNA and DNA viruses are zoonotic or have zoonotic origins in an animal reservoir that is usually mammalian and sometimes avian. Not all zoonotic viruses are transmissible (directly or by an arthropod vector) between human hosts. Virus genome sequence data provide the best evidence of transmission. Of human transmissible virus, 37 species have so far been restricted to self-limiting outbreaks. These viruses are priorities for surveillance because relatively minor changes in their epidemiologies can potentially lead to major changes in the threat they pose to public health. On the basis of comparisons across all recognized human viruses, we consider the characteristics of these priority viruses and assess the likelihood that they will further emerge in human populations. We also assess the likelihood that a virus that can infect humans but is not capable of transmission (directly or by a vector) between human hosts can acquire that capability.
Below is the list of the diseases that the report and the CDC consider to be those posing the most risk of a future pandemic. (Page 5 of the PDF you can view on this link) These are considered to be emerging viruses that pose a risk and for this reason diseases such as Ebola and influenza which are already established and are known to spread widely are not on the list.
The reason this distinction is made is that the diseases on the list below have shown they can infect humans but don’t yet have the capability to cause widespread contagion in humans – but are at the point where a relatively minor change would enable sustained spread through the population.
- Dandenong virus
- Guanarito virus
- Junin virus
- Lassa virus
- Lujo virus
- Lymphocytic choriomeningitis virus
- Machupo virus
- Sabia virus
- Andes virus
- Bwamba virus
- Crimean-Congo hemorrhagic fever virus
- Oropouche virus
- Rift Valley fever virus
- Severe fever with thrombocytopenia syndrome virus
- Middle East Respiratory syndrome coronavirus
- Lake Victoria Marburgvirus
- Sudan Ebolavirus
- Japanese encephalitis virus
- Usutu virus
- West Nile virus
- Nipah virus
- Colorado tick fever virus
- Nelson Bay orthoreovirus
- Bas-Congo virus
- Rabies virus
- Barmah Forest virus
- O’nyong-nyong virus
- Ross River virus
- Semliki Forest virus
- Venezuelan equine encephalitis virus
- Titi monkey adenovirus
- Macacine herpesvirus 1
- Simian virus 40
- Monkeypox virus
- Orf virus
- Vaccinia virus
Quite a list, and when you add influenza viruses and diseases such as Ebola it paints a very bleak picture.
As global healthcare stands currently we are not in a position where monitoring and reporting of disease is good enough. Depending on where an outbreak begins it can be well underway before measures are put in place to contain it.
The continuing growth in global travel, and the influx of people into cities from rural communities for economic reasons adds to the problem.
Finally many of these conditions use insects, primarily mosquitos as vectors…the middleman that allows the jump from animal to human. This is in my opinion one of the biggest problems we face. Mosquitoes and the viruses they carry are spreading. As an example the Aedes aegypti mosquito prefers to live indoors. It likes cities where there is ample supply of humans to feed on. Like all mosquitos it lays eggs in water and cities provide ample opportunities for water to collect in places it can go un-noticed.
Historically, Ae. aegypti was found in forested areas, using tree holes as habitats . As an adaptation to urban domestic habitats, it is nowadays exploiting a wide range of artificial containers such as vases, water tanks and tyres . It is also found utilising underground aquatic habitats, such as septic tanks , and adapting to use both indoor and outdoor aquatic container habitats in the same area. Adaptation to breeding outdoors may allow for increased population numbers and difficulty in implementation of control methods . A study in Brazil found high numbers of eggs in oviposition sites close to human populations . Eggs which are laid on or near the water surface  are resistant to desiccation . (source)
This adaptation will ultimately occur with other species compounding the problem as different species spread different diseases.
It’s also worth noting that if you are constantly bitten by mosquitos your body becomes used to it. You no longer notice the bites as the itch response ceases. This adds to the morbidity and mortality of the disease (serious illness and fatality numbers) because people have no idea they are sick until the symptoms of the disease itself develops. In diseases that have human to human transmission this is as disaster as the disease is being passed on unknowingly. This is often how a localised outbreak turns into an epidemic and an epidemic into a pandemic.
Pandemics pose a massive threat to all of us, look at the statistics of deaths from the Plague pandemic and the 1918-1920 flu pandemic. Both were responsible for tens of millions of deaths worldwide at a time when the global population was much lower. Today we have a couple of billion more hosts available to sustain a pandemic.
A while ago I wrote Controlling Infectious Disease Spread Using Social Isolation. This may be a good time for you to read it. In addition here are a few more articles you may find interesting:
- Clostridium Difficile: Using Pro-biotic Yogurt When antibiotics Fail
- Children Falling Ill With Polio-Like Illness