Since the hantavirus was discovered in 1993, less than 100 cases of HPS have been identified in 20 states. These states encompass the western half of the United States and most recently a few eastern states as well. Over half the people who get HPS die from the illness. In 1994, about two dozen cases have been confirmed. It is predicted that less than 50 cases will occur this year. So far the earliest known case dates back to 1975. Almost all cases have had evidence of close contact with rodents (deer mice or cotton rats).
Rodents are the primary reservoir host of the recognized hantaviruses. Each hantavirus appears to have a preferred rodent host, but other small mammals can be infected as well. Data strongly suggests that the deer mouse is the primary carrier of the hantavirus seen in all parts of the United States except the Eastern Coast and the Southeast. In the Southeast, the cotton rat has been identified as a carrier for the virus causing HPS. Evidence of infection has also been found in pinon mice, brush mice and western chipmunks. The deer mouse is highly adaptable and is found in different habitats, including human residences in rural and semirural areas, but generally not in urban centers.
Hantaviruses do not cause obvious illness in their rodent hosts. Infected rodents shed virus in saliva, urine, and feces for many weeks, but the duration and period of maximum infectivity are unknown.
Human infection may occur when infective saliva or excreta are inhaled as aerosols produced directly from the animal. Transmission may also occur when fresh or dried materials contaminated by rodent excreta are disturbed, directly introduced into broken skin, introduced into the eyes, or, possibly, ingested in contaminated food or water. Persons have also become infected after being bitten by rodents.
Ticks, fleas, mosquitos and other biting insects are not known to have a role in the transmission of hantaviruses. Person-to-person transmission has not been associated with any of the previously identified hantaviruses or with the recent outbreak in the Southwest. Cats and dogs are not known to be a reservoir host of hantaviruses in the United States. However, these domestic animals may bring infected rodents into contact with humans.
Hantavirus pulmonary syndrome does not appear to be limited to a particular age, race, ethnic group, or gender. The chance of exposure to hantavirus is greatest when individuals work, play or live in closed spaces where there is an active rodent infestation. It is important to be aware of possible rodent exposure, for example, when working in crawl spaces, opening phone line stations or using air condition equipment after winter storage.
Travel to and within all areas where hantavirus infection has been reported is safe. The possibility of exposure to hantavirus for campers, hikers, and tourists is very small and reduced even more if steps are taken to reduce rodent contact.
Cleaning of areas with small numbers of rodents should include wearing latex or rubber gloves and wetting down affected areas with general household disinfectant solutions such as Lysol or bleach and water or Amonia. Cleaning of areas with large numbers of rodents includes wearing latex or rubber gloves, goggles, HEPAfilter mask and wetting the area with disinfectant solutions or bleach and water.
Remember that the chances of getting HPS are very low. However, if you do get the disease, it can be very serious.
Introduction
The recently recognized hantavirus-associated disease among residents
of the southwestern United States and the identification of rodent
reservoirs for the virus in the affected areas warrant recommendations
to minimize the risk of exposure to rodents for both residents and
visitors. While information is being gathered about the causative
virus and its epidemiology, provisional recommendations can be made on
the basis of knowledge about related hantaviruses. These
recommendations are based on current understanding of the
epidemiologic features of hantavirus infections in the Southwest; they
will be periodically evaluated and modified as more information
becomes available.
Rodents are the primary reservoir hosts of recognized hantaviruses. Each hantavirus appears to have preferential rodent hosts, but other small mammals can be infected as well. Available data strongly suggest that the deer mouse (Peromyscus maniculatus) is the primary reservoir of the newly recognized hantavirus in the southwestern United States. Serologic evidence of infection has also been found in piñon mice (P. truei), brush mice (P. boylii), cotton rats (Sigmodon hispidus), and western chipmunks (Tamias spp.). P. maniculatus is highly adaptable and is found in different habitats, including human residences in rural and semirural areas, but generally not in urban centers.
Hantaviruses do not cause apparent illness in their reservoir hosts. Infected rodents shed virus in saliva, urine, and feces for many weeks, but the duration and period of maximum infectivity are unknown. The demonstrated presence of infectious virus in saliva of infected rodents and the marked sensitivity of these animals to hantaviruses following inoculation suggests that biting may be an important mode of transmission among rodents.
Human infection may occur when infective saliva or excreta are inhaled as aerosols produced directly from the animal. Persons visiting laboratories where infected rodents were housed have been infected after only a few minutes of exposure to animal holding areas. Transmission may also occur when dried or fresh materials contaminated by rodent excreta are disturbed, directly introduced into broken skin, introduced onto the conjunctivae, or, possibly, ingested in contaminated food or water. Persons have also become infected after being bitten by rodents.
Arthropod vectors are not known to have a role in the transmission of hantaviruses. Person-to-person transmission has not been associated with any of the previously identified hantaviruses or with the recent outbreak in the Southwest. Cats and dogs are not known to be reservoir hosts of hantaviruses in the United States. However, these domestic animals may bring infected rodents into contact with humans.
Known hantavirus infections of humans occur primarily in adults and are associated with domestic, occupational, or leisure activities that bring humans into contact with infected rodents, usually in a rural setting. Patterns of seasonal occurrence differ, depending on the virus, species of rodent host, and patterns of human behavior, cases have been epidemiologically associated with the following situations:
The reservoir hosts of the hantavirus in the southwestern United States also act as hosts for the bacterium Yersinia pestis, the etiologic agent of plague. Although fleas and other ectoparasites are not known to play a role in hantavirus epidemiology, rodent fleas transmit plague. Control of rodents without concurrent control of fleas may increase the risk of human plague as the rodent fleas seek an alternative food source.
Eradicating the reservoir hosts of hantaviruses is neither feasible nor desirable. The best currently available approach for disease control and prevention is risk reduction through environmental hygiene practices that deter rodents from colonizing the home and work environment.
Box 1. General precautions for residents of affected areas Eliminate rodents and reduce the availability of food sources and nesting sites used by rodents inside the home.
Prevent rodents from entering the home. Specific measures should be adapted to local circumstances.
Box 2. Eliminating rodent infestation: Guidance for residents of affected areas Before rodent elimination work is begun, ventilate closed buildings or areas inside buildings by opening doors and windows for at least 30 minutes. Use an exhaust fan or cross ventilation if possible. Leave the area until the airing-out period is finished. This airing may help remove any aerosolized virus inside the closed-in structure. Second, seal, screen, or otherwise cover all openings into the home that have a diameter of greater than or equal to ³1/4 inch. Then set rodent traps inside the house, using peanut butter as bait. Use only spring- loaded traps that kill rodents. Next, treat the interior of the structure with an insecticide labeled for flea control; follow specific label instructions. Insecticide sprays or powders can be used in place of aerosols if they are appropriately labeled for flea control. Rodenticides may also be used while the interior is being treated, as outlined below. Remove captured rodents from the traps. Wear rubber or plastic gloves while handling rodents. Place the carcasses in a plastic bag containing a sufficient amount of a general-purpose household disinfectant to thoroughly wet the carcasses. Seal the bag and then dispose of it by burying in a 2- to 3-foot-deep hole or by burning. If burying or burning are not feasible, contact your local or state health department about other appropriate disposal methods. Rebait and reset all sprung traps. Before removing the gloves, wash gloved hands in a general household disinfectant and then in soap and water. A hypochlorite solution prepared by mixing 3 tablespoons of household bleach in 1 gallon of water may be used in place of a commercial disinfectant. When using the chlorine solution, avoid spilling the mixture on clothing or other items that may be damaged. Thoroughly wash hands with soap and water after removing the gloves. Leave several baited spring-loaded traps inside the house at all times as a further precaution against rodent reinfestation. Examine the traps regularly. Disinfect traps no longer in use by washing in a general household disinfectant or the hypochlorite solution. Disinfect and wash gloves as described above, and wash hands thoroughly with soap and water before beginning other activities.
NOTE: EPA-approved rodenticides are commercially available. Instructions on product use should always be followed. Products that are used outdoors should be specifically approved for exterior use. Any use of a rodenticide should be preceded by use of an insecticide to reduce the risk of plague transmission. Insecticide sprays or powders can be used in place of aerosols if they are appropriately labeled for flea control.
Box 3. Clean-up of rodent-contaminated areas: Guidance for residents of affected areas
Persons involved in the clean-up should wear rubber or plastic gloves. Spray dead rodents, rodent nests, droppings, or foods or other items that have been tainted by rodents with a general-purpose household disinfectant. Soak the material thoroughly, and place in a plastic bag. When clean-up is complete (or when the bag is full), seal the bag, then place it into a second plastic bag and seal. Dispose of the bagged material by burying in a 2- to 3-foot-deep hole or by burning. If these alternatives are not feasible, contact the local or state health department concerning other appropriate disposal methods. After the above items have been removed, mop floors with a solution of water, detergent, and disinfectant. Spray dirt floors with a disinfectant solution. A second mopping or spraying of floors with a general-purpose household disinfectant is optional. Carpets can be effectively disinfected with household disinfectants or by commercial-grade steam cleaning or shampooing. To avoid generating potentially infectious aerosols, do not vacuum or sweep dry surfaces before mopping. Disinfect countertops, cabinets, drawers, and other durable surfaces by washing them with a solution of detergent, water, and disinfectant, followed by an optional wiping-down with a general-purpose household disinfectant. Rugs and upholstered furniture should be steam cleaned or shampooed. If rodents have nested inside furniture and the nests are not accessible for decontamination, the furniture should be removed and burned. Launder potentially contaminated bedding and clothing with hot water and detergent. (Use rubber or plastic gloves when handling the dirty laundry; then wash and disinfect gloves as described in the section on Eliminating Rodents Inside the Home.) Machine-dry laundry on a high setting or hang it to air dry in the sun.
Box 4. Special precautions for clean-up in homes of persons with hantavirus infection or buildings with heavy rodent infestation
A baseline serum sample, preferably drawn at the time these activities are initiated, should be available for all persons conducting the clean- up of homes or buildings with heavy rodent infestation. The serum sample should be stored at -20 C. Persons involved in the clean-up should wear coveralls (disposable if possible), rubber boots or disposable shoe covers, rubber or plastic gloves, protective goggles, and an appropriate respiratory protection device, such as a half-mask air-purifying (or negative-pressure) respirator with a high-efficiency particulate air (HEPA) filter or a powered air-purifying respirator (PAPR) with HEPA filters. Respirators (including positive-pressure types) are not considered protective if facial hair interferes with the face seal, since proper fit cannot be assured. Respirator practices should follow a comprehensive user program and be supervised by a knowledgeable person. Personal protective gear should be decontaminated upon removal at the end of the day. If the coveralls are not disposable, they should be laundered on site. If no laundry facilities are available, the coveralls should be immersed in liquid disinfectant until they can be washed. All potentially infective waste material (including respirator filters) from clean-up operations that cannot be burned or deep buried on site should be double bagged in appropriate plastic bags. The bagged material should then be labeled as infectious (if it is to be transported) and disposed of in accordance with local requirements for infectious waste. Workers who develop symptoms suggestive of HPS within 45 days of the last potential exposure should immediately seek medical attention. The physician should contact local health authorities promptly if hantavirus- associated illness is suspected. A blood sample should be obtained and forwarded with the baseline serum through the state health department to CDC for hantavirus antibody testing.
Box 5. Precautions for workers in affected areas who are exposed to rodents
A baseline serum sample, preferably drawn at the time of employment, should be available for all persons whose occupations involve frequent rodent contact. The serum sample should be stored at -20C. Workers in potentially high-risk settings should be informed about the symptoms of the disease and be given detailed guidance on prevention measures. Workers who develop a febrile or respiratory illness within 45 days of the last potential exposure should immediately seek medical attention and inform the attending physician of the potential occupational risk of hantavirus infection. The physician should contact local health authorities promptly if hantavirus-associated illness is suspected. A blood sample should be obtained and forwarded with the baseline serum through the state health department to CDC for hantavirus antibody testing. Workers should wear a half-face air-purifying (or negative-pressure) respirator or PAPR equipped with HEPA filters when removing rodents from traps or handling rodents in the affected area. Respirators (including positive-pressure types) are not considered protective if facial hair interferes with the face seal, since proper fit cannot be assured. Respirator use practices should be in accord with a comprehensive user program and should be supervised by a knowledgeable person. Workers should wear rubber or plastic gloves when handling rodents or handling traps containing rodents. Gloves should be washed and disinfected before removing them, as described above. Traps contaminated by rodent urine or feces or in which a rodent was captured should be disinfected with a commercial disinfectant or bleach solution. Dispose of dead rodents as described in the section on Eliminating Rodents inside the Home. Persons removing organs or obtaining blood from rodents in affected areas should contact the Special Pathogens Branch, Division of Viral and Rickettsial Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, [telephone (404) 639-1115] for detailed safety precautions.
Box 6. Reducing risk of hantavirus infection: Guidance for hikers and campers
Avoid coming into contact with rodents and rodent burrows or disturbing dens (such as pack rat nests). Do not use cabins or other enclosed shelters that are rodent infested until they have been appropriately cleaned and disinfected. Do not pitch tents or place sleeping bags in areas in proximity to rodent feces or burrows or near possible rodent shelters (e.g., garbage dumps or woodpiles). If possible, do not sleep on the bare ground. Use a cot with the sleeping surface at least 12 inches above the ground. Use tents with floors. Keep food in rodent-proof containers. Promptly bury (or--preferably--burn followed by burying, when in accordance with local requirements) all garbage and trash, or discard in covered trash containers. Use only bottled water or water that has been disinfected by filtration, boiling, chlorination, or iodination for drinking, cooking, washing dishes, and brushing teeth.
To receive additional recommendations for the prevention and control of hantavirus infections associated with rodents in the United States, you will need to call 404-332-4565 and follow the prompts. The following documents on Hantavirus are available: 310031, Hantavirus Illness in the United States; 310032, Hantavirus Illness Prevention Information; 310033, Guidelines for Removing Organs or Obtaining Blood from Rodents Potentially Infected with Hantavirus; 310034, Laboratory Management of Agents Associated with Hantavirus Pulmonary Syndrome: Interim Biosafety Guidelines; 310035, State Contacts for Hantavirus Information
Ebolaboy - May 23, 1995