A Plague of Diseases That Won’t Go Away

I was at least a little alarmed at a report this week that the National Park Service has closed a campground in Yellowstone National Park because of the plague. As you may recall from a class in world history, the plague is spread by insects, usually fleas, and the most common host for these fleas is the nearest available rodent. In this case the culprit appears to be squirrels, so the Park Service is going to spray all the squirrel burrows they can find for fleas.

While the plague may seems like a relic, many diseases that we think of as eradicated are still very much with us. Our CDC puts out a publication called Morbidity and Mortality Weekly Report (MMWR) that tracks 50 or so diseases. Some of them are what you’d expect: flu, tuberculosis, food poisoning, and sexually transmitted diseases. But others seem transported from another place or another time: yellow fever, leprosy (now called Hansen’s disease), and, yes, the plague.

So far this year there have been 2 confirmed cases of plague in the US, after 10 last year. Most cases arise in the mountain West and far West: Nevada, Colorado, California, etc. The last true outbreak of plague in this country was in 1924 in Los Angeles, in which 30 people died. Before that outbreaks had occurred in San Francisco and Oakland that killed more than 100 people.

Making Sense of the Numbers

Here are the MMWR disease tables for the most recent week. When you scan through them, some really interesting (to me, anyway) things pop up. For example:

  • Of the diseases addressed by the MMR and DPT vaccines that create so much controversy, only whooping cough seems to have regained a hold in this country, with more than 19,000 cases last year. In 2014 for mumps the total was under 1,000; for measles 667; and for diphtheria, rubella (German measles), and tetanus combined only 22 cases.
  • Leprosy seems to be holding steady at 80–100 cases a year over the last several years.
  • Tropical diseases are still with us: yellow fever, Q fever, malaria, etc.
  • Only 12 cases of human rabies in 2010 through 2014 combined.
  • Diseases that make the news—think anthrax, ebola, and West Nile virus—come and go. The last confirmed case of anthrax was in 2011, only 6 cases of ebola, and West Nile fell to 414 in 2014 down from nearly 10,000 cases at the peak in 2003.

I don’t think there’s much profound here, but the numbers do help me make sense of what I see in the news.