Rabies is a significant concern for researchers handling bats, not because bats exhibit a higher incidence of rabies infection than other wild mammals, but because without prompt treatment rabies is nearly always fatal in humans. The virus is most commonly transmitted via contact with infected saliva through a bite, but other means of transmission include contact of infected saliva and nervous tissue with mucous membranes of the mouth, nose and eyes. There have also been two cases of transmission by aerosolized rabies virus in a Texas cave (Constantine, 1988), but no other cases have been reported since. A bat infected with rabies is not aggressive, but rather lethargic and incapacitated as the virus spreads through its nervous system causing paralysis. Thus, the main source of rabies infection from bats is inappropriate handling of the sick animal which bites in self-defense.
Symptoms of rabies usually develop 10-14 days after exposure and include pain, burning and numbness at the site of infection, headaches, insomnia, fever, and difficulty swallowing. However, usually by the time the symptoms are apparent, the progression of the disease can no longer be prevented, ultimately resulting in fatal inflammation of the brain and spinal cord. Therefore, it is imperative that a person seek immediate medical attention after any potential exposure. People handling bats should obtain pre-exposure immunization, which is conferred by 3 doses of vaccine, and check their titers regularly. Additionally, they should simply avoid exposure. Bats captured to establish a captive colony should be quarantined for at least 6 months to assess possible sickness. Always wear gloves when handling bats and avoid rapid and unpredictable movements which increase the chance of bites.
Histoplasmosis Histoplasmosis is a respiratory infection caused by the fungus Histoplasma capsulatum, which develops well in organic materials such as bat and bird feces. Fungal spores become airborne when dry guano is disturbed and can be inhaled resulting in infection. Greatest likelihood of infection is in caves and mines with large guano accumulations where warmth and humidity enhance growth of the fungus, though cases of infection in buildings with large bat populations have also been reported (Smith, 1955). Symptoms of histoplasmosis usually appear one or two weeks after exposure and range from a dry-cough, chest pain and labored breathing to fever, nightsweats, weight loss and even blood-stained sputum. Histoplasmosis can be fatal. Persons entering a potentially contaminated roost should wear respirators with 2 micron filters and should bathe soon after departing the roost.
Hazardous atmospheric gases Caves, mines, and other underground spaces are poorly ventilated, which can result in the accumulation of noxious gases and/or dangerously low concentrations of oxygen. These gases include irritants such as ammonia and sulfur dioxide, asphyxiants such as nitrogen, methane and carbon dioxide, and toxic asphyxiants such as carbon monoxide and hydrogen sulfide (Constantine, 1988). Several of these gases are odorless, and the concentration of others may increase due to the presence of large amounts of guano. One of the authors (ABR) has experienced respiratory distress and nausea from nitrogenous fumes emitting from vampire bat guano. A researcher should always obtain as much information as possible about a cave or mine prior to entering it and may wish to use portable toxic gas detectors during exploration.
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