A deer mouse trapped during routine monitoring last week in Chula Vista has tested positive for the potentially-deadly hantavirus.
Fifty-two rodents have tested positive for hantavirus in the county this year, compared to 21 in 2010.
It can cause hantavirus pulmonary syndrome, which begins with flu-like symptoms but can grow into severe breathing difficulties and even death.
The best way to prevent the disease is to keep mice out of houses, garages and sheds by sealing holes larger than the size of a dime.
