Is Montana at Risk?
Identified Hazards for the State of Montana
Basic Disaster Information:
VECTOR-BORNE DISEASES
Vectors are organisms (e.g., insects, animals, etc.) Which may adversely affect the public health and well-being by directly or indirectly transporting or transmitting a disease-causing agent, or which may cause other health trauma (Moy and Quickenden, 1976). Vector-borne diseases which have been diagnosed in Montana include: Western equine encephalitis, St. Louis encephalitis, Colorado tick fever, Rocky Mountain spotted fever, tularemia, rabies, plague, and most recently, Hanti-Virus.
As long as vectors are present in the state, the potential for recurring disease exists. A number of factors influence this potential: areas of historical occurrence, time of year, vector habitat availability and incident of human exposure. Based on historical incidence, the vector-borne diseases to which Montanans are most vulnerable are Western equine encephalitis, St. Louis encephalitis, Rocky Mountain spotted fever, Colorado tick fever, tularemia and Hanti-Virus.
Reported cases of Wester equine encephalitis have typically been higher in irrigated areas east of the Continental Divide. In most areas, more than 90 percent of all mosquito production may be associated with the use of water for irrigation. In non-irrigated areas, snow melt pools, spring run-off into low areas or depressions and a rising water table account for higher percentage of mosquitos produced. Flooding creates additional breeding sites. These same areas may be considered vulnerable to the incidence of St. Louis encephalitis. The likelihood of this disease infecting the population is greater in the high mountainous areas of the state.
Colorado tick fever has historically been associated chiefly with the southwestern quarter of the state while cases of Rocky Mountain spotted fever have been most numerous in the southern half of the state. As long as favorable tick habitat exists in these regions and within close proximity to populated areas, these portions of the state should be considered most vulnerable to future incidence of tick fever.
Most, but not all cases of tularemia appear to be associated with ticks in the southeastern part of the state. As with the other tick-borne diseases caution should be observed in tick-infested areas in this portion of the state or when handling wild rabbits or rodents.
The deer mice are the rodents carrying hantaviruses that cause hantavirus pulmonary syndrome. These rodents shed the virus in their urine, droppings and saliva. The virus is mainly transmitted to people when they breathe in air contaminated with the virus. This happens when fresh rodent urine, droppings or nesting materials are stirred up. When tiny droplets containing the virus get into the air, this process is known as " aerosolization."
There are several other ways rodents may spread hantavirus people:
If a rodent with the virus bites them, the virus may be spread this way, but this is very rare. Researchers believe that you may be able to get the virus if you touched something that had been contaminated with rodent urine, droppings or saliva, and then touched your nose or mouth. Researchers also suspect that if virus-infected rodent urine, droppings or saliva contaminates food that you eat, you could also become sick. That is another reason why disinfecting rodent-infested areas is so important in preventing transmission of the virus.
Transmission can happen anyplace that infected rodents have infested. This could be barns or sheds or other outbuildings, warehouses or summer cottages closed up for the season. But carrier rodents infest homes as well! Therefore, the most sensible way to avoid contact with rodents is to prevent rodents from infesting the places where you live and work, and to follow safety precautions if you do stumble into a rodent-infested area.
Control of these diseases varies depending on whether or not an intermediate host is involved. In the case of direct infection with a mosquito-borne disease, control is most effectively approached through management of the vector itself. Tick-borne diseases involve an intermediate reservoir of infection and therefore are more difficult to control. Avoidance tactics are the only suggested mitigative measures to date for minimizing tick-borne disease transmission.
A comprehensive public awareness program informing people of the disease potential and actions they might take to lessen their vulnerability would be the greatest step toward successful elimination of vector-borne diseases in this state.
