Ted Brown's first clue that this could be a bad year for plague was a diseased cat from Tucumcari.
Heavy summer rains and few cases the last couple of years were other signals that 1991 could be the start of another cycle of increasing instances of plague, both in animals and humans.
"Once the curve starts upward, it tends to go rather steep for the first couple of years," says Brown, a vector control specialist with the New Mexico Environmental Improvement Division. "A doubling of animal cases or human cases has been shown in the past."
New Mexico for years has led the nation in human plague cases, and 1991 is no different. Of the eight cases nationally so far this year, three have been in New Mexico, two in Colorado and one each in Arizona, Oklahoma and Utah.
Last year was the first since 1972 that no human plague cases were reported in New Mexico; only one animal was found to have the disease in 1990.
Plague, the scourge that wiped out a quarter of the population of medieval Europe, has been on a downhill slope in New Mexico since 1983, when 26 human cases were confirmed, the most in any year since 1949.
The first 1991 case was confirmed in February in the Tucumcari cat. Brown says a Tucumcari cat also was one of the first confirmed cases in the early 1980s before a 1983 peak.
"I said, 'Ah, back in the '80s again. Let's see what the rest of the year holds,"' Brown says.
The year held little until September, when all three New Mexico cases were reported within the same week. Officials believe the victims, a 5-year-old girl and a couple in their 50s, all contracted the disease in the same northern New Mexico area.
Other cases have been in a 45-year-old Arizona man, a 13-year-old Oklahoma boy, a 14-year-old Utah boy and a 7-year-old girl and a 51-year-old man in Colorado.
Nobody has died from plague this year.
Health officials had concluded in an April, 1988, report that a plague cycle exists, with peak years in 1961, 1965, 1970, 1975, 1980 and 1983.
State epidemiologist Dr. Mack Sewell agrees that New Mexico is due for an increase in plague, but says it is impossible to predict when the surge will hit.
"I'm sure we're going to see more plague activity, that's inevitable," Sewell says. "Whether we'll start seeing more in the next year or two, nobody knows for sure."
There have been 193 human plague cases in New Mexico since 1949, resulting in 28 deaths, an 86% survival rate, Brown says. Early detection and improved treatment have helped increase the survival rate.
And Brown partially credits increased public awareness for the drop in human cases.
Dusting rodent burrows with flea repellent is one of the few steps that can be taken to keep wild animals from becoming hosts to plague-infested fleas, Brown says.
Most human victims contract the disease from infected fleas. Brown says rock squirrels are the most popular host for the fleas because fleas usually found on the animals are susceptible to plague.
There have been 105 varieties of fleas identified in New Mexico, 33 of which are involved in plague, Brown said.
The majority of plague cases occur in June through September, warm months when the rodents that are the principal hosts to plague-infected fleas are most active.
Heavy rains this year have provided an abundance of water and food for rodents and fleas.
"When you have a rainy season like we're having now, the humidity is higher, the weeds are thick, and the fleas can wander to another host," Brown says.
Brown says a rock squirrel population near a rural housing area south of Santa Fe was virtually eliminated several years ago. But plague-infested rodents have returned to the area, and three of the four rock squirrels that have been confirmed this year were found in that housing area, Brown says.
He says there is no specific reason why so many cases are in Santa Fe, but contributing factors may be that plague is more concentrated and active in the area and that people may be more willing to report suspect animals since the agency is based in Santa Fe.
Plague symptoms resemble those of flu and include headache, fever, chills and possibly enlarged lymph nodes.
Brown says people can ward off plague by using insect repellent on themselves, flea powder on pets and avoiding and reporting dead animals.
Brown says 85% to 90% of plague victims in New Mexico contract the disease within a mile from home. "People aren't going out into the wilderness and getting plague."