Thursday, June 25, 2015

The T-rex you can't see

Blog post #32


The latest Jurassic film shows people being chomped up by T-Rex hybrids, (No spoiler alert here. You have to be comatose to have missed the previews), carried off by flying lizards, and gulped down by some sea monster certain to inhabit the dreams of the kids who see the film. Unless you are a creationist you recognize the absurdity while enjoying the fun of seeing the visual reconstruction of these creatures. The real creature that haunts the dreams of Public Health workers today is invisible.

Tyrannosaurus rex never killed any humans. Yersinia pestis has killed tens of millions. The organism is somewhere around a hundred times smaller than one of the pixels you are looking at. The plague in its various forms killed 25 million people during a 200 year epidemic in the last millennium. The numbers may have been bigger but no one was counting large parts of the world outside of Europe, North Africa and parts of Asia. Some say the fall of Rome may have been caused by a pandemic brought back by troops returning from Persia. Seventeen days ago the septicemic version killed a sixteen year old boy near Ft. Collins Colorado.
My familiarity with this tiny killer comes from a part-time job I had in college. Several entomology students were hired by the Public Health Service to trap and collect rats along the Guadalupe River corridor in San Jose. We set snap traps along the river from the bay to the source in the Almaden Hills. The rats, mostly Rattus rattus, carried fleas, and the specific fleas we were looking for were the commonest carrier of plague bacteria. Many fleas can carry the bacterium but only two species have caused the pandemics. We taped our sleeves around gloves and shook flea powder on the arms and our pants cuffs and used long wooden tongs to pick up traps and dead rats and dropped them in a plastic bag which we sealed. In the lab we identified fleas and sent the likely ones to a USPHS lab in San Francisco for analysis. No plague was found but we know it was present in fleas on small mammals in the Coast Range of San Mateo County and in the San Bruno Hills.
North America was free of plague until ships brought the rats from Europe and Asia. Now it is endemic in populations of small mammals in the west. Northern New Mexico and Southern Colorado are centers of activity but it occurs throughout the west. When people hunt squirrels and other small mammals or live in dwellings supporting flea populations they can be susceptible to the plague. During the middle ages, any priest or lay-healer could diagnose the bubonic version. Today many physicians have never seen the symptoms and may miss the diagnosis. Pneumonic plague occurs when the lungs get affected and can then be transmitted through coughing.
The good news is it’s treatable if diagnosed early. Unfortunately the boy in Colorado caught the fast-track version and evidently died within a week of contracting it. There are still a thousand or more cases reported around the world and probably many more unreported. Anyway, this is a darn good reason to stop feeding squirrels in the parks. Avoid dead or sick appearing mammals when hiking. The fleas will be looking for a convenient replacement for their meal ticket.

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