Tuesday, October 16, 2012

Get ready for the next pandemic of an emerging disease

An article in The Economist points out that "zoonotic infections, those that pass from animals to humans...........make up nearly two-thirds of all human infectious diseases, including rabies, Ebola and malaria. The three most recent outbreaks—of SARS, bird flu and swine flu—indicate that the next pandemic is likely to be zoonotic in origin." The implication is that one-third of infectious diseases arose in humans (or that the animal origin has not been identified).

It seems logical that as the number of humans increases and humans occupy more of the earth's surface, there will be more opportunities for diseases of animals to pass to humans. The more such events take place, the greater the chance that one of these infections will prove to be pandemic, or will be transformed in humans to be pandemic. Flu pandemics have emerged every few decades as a new strain emerges that is easily transmitted, quite infectious, and for which there is not much resistance in the population. If the strain is virulent, lots of people die.

Infectious diseases need to circulate in the human population. Many infections that enter the human population infect a few (or many) people and then disappear when no new people are infected. This may happen when the human population is sparse or when a the people where the disease emerged are not connected with other people. The greater the population, the denser it is; the better the communications, the less likely a group is to be isolated from others.

It therefore stands to reason that more pandemics will occur. In the last century we saw several flu pandemics, including "the Spanish flu" which is estimated to have killed 50 million people or more and the HIV pandemic which is on its way to causing similar human mortality.

We need a strong international surveillance system. We also need to keep biomedical research going to have more tools available to the medical profession to prevent infection and treat the infected. We also need to keep our public health toolbox (containing our ability to use such interventions as quarantine, isolation of the infected, and even reduction of person to person contacts).