Not all diseases can be transmitted from animals to humans. Those that can make the leap from species to species are called zoonotic diseases. Without proper protection and handling, it's possible for humans to contract some illnesses from cows.
Methods of Transmission
Cattle transmit zoonotic diseases to humans a variety of ways. An infected cow’s bodily fluids -- such as blood, tissue, urine, semen and feces -- contain pathogens including bacteria, viruses and some parasites. Direct contact with these substances transfers the microorganisms to humans through the mucous membranes of their mouths, noses or eyes. Other modes of transmission include ingestion of the pathogen through contaminated food or water, contact with contaminated surfaces or aerosolized droplets in the air, or even insect transmission such as tick bites.
Escherichia coli (E. coli) and salmonella are probably two of the best-known illnesses caused by bacteria. These diseases, in addition to another called campylobacter, commonly spread from cattle to humans through contact with feces or through indirect consumption of undercooked or contaminated meat or unpasteurized milk products. Leptospirosis is another disease that affects livestock animals. Direct contact, inhalation or ingestion can transmit the bacteria to humans, potentially causing liver and kidney disease. Listeriosis is an illness caused by bacteria residing in wet, rotting vegetation. Most humans, except those who are immunosuppressed, are resistant to infection.
Q fever causes abortions in cattle and is transmitted to humans through contaminated reproductive fluids, tissues and milk. Humans can develop hepatitis and pneumonia. Bovine tuberculosis and brucellosis are shed through bodily fluids, respiratory secretions or infected milk. Both diseases are now uncommon due to federal eradication programs. A bacterial skin disease called dermatophilosis, or rain rot, is spread through contact with the infected skin or biting insects. Human infections are rare.
Anthrax is a serious bacterial disease of cattle and other animals. The bacteria Bacillus anthracus forms spores that can remain in the environment for years. Cattle ingest the spores; human handlers can get them through skin wounds, inhalation of contaminated dust or eating undercooked meat.
Rabies is a common deadly viral disease transmitted to humans by a variety of animals, including cattle, through saliva or animal bites. It's fatal to infected animals; any human that has contact with a rabid cow should contact a physician for prophylactic injections. Pseudocowpox is a virus that causes sores and scabs on a cow’s udders. Humans can get sores on their arms and hands if they come in direct contact with the infected area. Vesticular stomatitis is a viral disease that causes sores on the infected cow’s feet and mouth. This disease can transfer to humans through direct contact; it causes flulike symptoms and sores.
Cryptosporidium is a protozoan parasite that causes diarrhea, mostly in young calves. Direct contact or ingesting contaminated food or water can transmit the parasite. Humans may show no signs or they may exhibit gastrointestinal symptoms. Giardiasis, caused by the parasite Giardia lamblia, may or may not exhibit symptoms in the cow. It's a widespread parasite found in food, soil or water contaminated with feces and spread through ingestion of contaminated substances. It can cause diarrhea and cramping in humans.
Other illnesses that can be transferred to humans from cows include the fungal disease ringworm, a skin infection that causes crusty, itchy patches on the skin. Direct contact can cause the same symptoms in humans. Finally, bovine spongeform encephalopathy (BSE) is a neurological disorder of cattle caused by an infection from the unusual protein called a prion. Theoretically, for unknown reasons, the normal prion protein becomes pathogenic and harms the nervous system. There is evidence, according to the Centers for Disease Control, that by eating BSE-contaminated food humans have acquired a human form called Creutzfeldt-Jakob disease.
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