WAILUKU, Maui — The state Department of Health has begun spreading rodent poison in brush areas in South Maui after recording a substantial increase in the number of mice caught in monitoring traps.

Traps that normally attract one or two mice each have been collecting 20 to 30 or more of the critters in recent weeks, as rain has made food plentiful, said Dr. Lorrin Pang, Maui district health officer.

Once drier weather prevails, the mice can be expected to infiltrate homes in search of food and water, raising concerns about another outbreak of murine typhus, a bacterial infection transmitted by fleas that live on rodents.

"The mice are waiting, they are knocking at the door," Pang said.

Maui suffered a murine typhus outbreak in 2002, when 35 cases were reported on the Valley Isle out of 46 cases statewide.

Cases spiked again in 2005, when there were 46 cases statewide, 39 of those on Maui. Last year, there were 17 cases statewide, 13 on Maui.

Those with murine typhus have flu-like symptoms that include headache, backache, high fever, nausea, vomiting, abdominal pain, a hacking, dry cough, and a dull red rash that begins on middle of the body and spreads. The disease is treated with antibiotics, and although death is rare, some of the Maui patients became ill enough to require hospitalization.

In response to the 2002 mouse invasion, the Health Department received approval from the U.S. Environmental Protection Agency for a special permit to allow vector-control crews to hand-spread an oat mixture containing the rodenticide zinc phosphide on large tracts of vacant land on Maui.

LIMITED IN LAHAINA

However, the U.S. Fish and Wildlife Service limited application of the rodenticide in Lahaina, another trouble spot, to less-efficient bait stations to protect endangered nene geese that inhabit the West Maui Mountains.

Zinc phosphide is often recommended as a rodenticide because it is fairly specific for rodents and there is little risk of secondary poisoning to animals that come into contact with poisoned mice or rats.

Leeward O'ahu experienced a similar rodent explosion problem last summer, forcing the state to distribute bait stations containing zinc phosphide.

Department of Health vector-control officials were unavailable Wednesday to comment on whether the rodent problem has recently surfaced on other islands. Department spokeswoman Janice Okubo said she was not aware of any such reports, and that routine rodent control using zinc phosphide was expected to begin again in the spring.

MANY FEMALES CAUGHT

On Maui, Pang said vector-control officials were initially puzzled as to why "99 percent" of the mice being caught in the traps were female. Upon consulting an expert, they learned that when pregnant females are close to giving birth, they go into a wider-ranging "foraging frenzy" to consume special nutrients they will need as mothers.

The presence of so many female mice could be a bad omen, prompting early action to control the rodent population in the drier South Maui area. Pang said the oat mixture is being spread along the edges of brush areas.

Reach Christie Wilson at cwilson@honoluluadvertiser.com.