Monday, Oct. 31, 2005 | 8:35 a.m.
After more than two years of not rooting out roof rat colonies in the valley, the Clark County Health District has scheduled its second major roof rat surveillance program planned for January.
This time around the rat patrol is targeting more than a dozen streets in Summerlin, Northwest Las Vegas, southwest Clark County and south central Las Vegas.
The last -- and only -- roof rat surveillance project conducted by the Health District was Sept. 26 to Oct. 10, 2003, in the Scotch 80s at West Charleston Boulevard and South Rancho Drive and at McNeil Estates between Charleston, Rancho, Sahara Avenue and Valley View Boulevard.
"We've had to hold off on roof rat surveillance because we have been focusing on mosquitoes and West Nile virus," said Daniel Maxson, Clark County's environmental health supervisor, who has been trapping rats locally for three decades.
"Roof rats currently are a pest control issue that we are monitoring. Mosquitoes, however, are a public health concern."
Though rats are now in several schools and being reported in a growing number of local neighborhoods, that does not necessarily mean the roof rat population is significantly on the rise or that the rodents are any greater a threat to human health than a year ago, Maxson said.
"I am going to wait to answer that question until after we do the 2006 surveillance to determine how healthy and well established the population is," Maxson said. "We have not completed enough work to make that determination."
A surveillance program includes trapping, capturing and killing the rats, then conducting blood tests for diseases that can harm humans, as well as measuring and weighing the animals, testing stool samples and examining female reproductive systems. The data then is analyzed and put into a report that Health District officials use to determine the severity of the infestation.
Finding the time to do that work has been a challenge because the Health District has been busy with Western equine encephalitis, St. Louis encephalitis and a host of other environmental concerns.
By putting roof rats on the back-burner this past summer -- except for the trappings in August at two Summerlin schools -- health officials say they were able to set at least 10 times the number of mosquito traps than last year.
That, Maxson said, undoubtedly played a role in the county's human cases of West Nile decreasing from 22 last year to seven this year.
The West Nile threat typically ends when colder weather kills off the summer mosquito population.
To date, all roof rats captured by Health District officials -- including 43 trapped during the first surveillance project in 2003 -- have been found to be free of diseases harmful to humans, including plague and hantavirus.
Roof rats are large black rodents that thrive in areas where there is much vegetation and water. They also tend to work their way into attics and have a tendency to gnaw through wires.
They are not indigenous to the Southern Nevada, Maxson said, noting they often come in as stowaways on palm and fruit trees that are shipped here.
In the valley, roof rats have been a problem in the posh Rancho Circle and Spanish Trail neighborhoods in Las Vegas and at Anthem in Henderson, where there are plenty of large trees and lots of water from lush landscaping.
Some people figure that the best way to combat them is to make sure no food -- no fruit trees, no dog food, etc. -- is available for the rats anywhere near homes.
However, Vivek Raman, a Health District environmental health specialist who conducted the 2003 surveillance program and authored the project's report, said that can backfire if it is done after the rats are already established in the neighborhood.
"If the rats can't find food outdoors, they will try to go indoors," Raman said.
"I would rather have a fat rat running around outdoors than a skinny, hungry rat inside."
Maxson said: "I'd just as soon they all starve to death."
Ed Koch can be reached at 259-4090 or at [email protected].
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