Occupational Health & Safety Issues

Although it is not common for personnel to become sick from a disease agent carried by the farm animals, called "zoonotic" diseases, the risk is ever present. Many bacteria and viruses are transmitted to humans by the oral route. This means, that if your hands have been contaminated by touching something loaded with bacteria or viral particles and you do not wash your hands, you can inadvertently introduce the bacteria or viral particles into your own mouth when you do things such as touch food as you put it into your mouth, rub the corner of your mouth, smoke your cigarette, or even put on chapstick! Rubbing your eyes also can lead to an infection.

The primary method to protect oneself from a zoonotic agent is to practice good personal hygiene.


Steps to Prevent Disease Transmission from Animals to Man

  1. Wash your hands with soap and water after handling animals, manure or urine, or animal products such as: milk, meat, wool, rumen samples, blood, fluids draining from wounds and placental membranes.
     
  2. Never eat or drink in areas where animals, animal wastes, or animal products are being handled.  
     

  3. Never drink milk which has not been pasteurized.  Never eat meat which has not been inspected and approved by the U.S.D.A.
     

  4. Report all suspected sick animals as soon as possible so that the Farm Animal Veterinarian may determine the cause of the illness and implement any additional protective steps.
     

  5. It is best to wear a designated pair of shoes and jeans or coveralls while working at the farm (don't wear these items elsewhere).  If items must be worn off the premises, clean the shoes very well by removing manure with brush and spray with commercial disinfectant before getting into car to go home.  Wash coveralls at the farm unit to reduce risk of contamination.  If they must be washed at home, separate the items from all family wash and rinse the machine with disinfectant afterward to avoid contamination.

The list of possible zoonotic diseases is quite extensive. A few of these diseases are discussed here, either because of their serious nature, or because they are more common in agricultural settings such as the university farms.

RAW MILK

This milk which has not been appropriately temperature treated (pasteurized) to ensure that bacterial counts are reduced to a safe level. No person is to drink raw milk from the university dairy-either from a cow's side, from the bulk tank, or any small samples taken at any other time. The same prohibition would be true for raw milk from sheep or goats. Although raw milk from a healthy animal which has been properly cooled and handled probably is safe, the list of disease agents which can be transmitted through unpasteurized milk is long and includes viruses, bacteria, rickettsia, fungi, and protozoa.

BRUCELLOSIS

Caused by a bacteria, Brucella sp., which is shed in large numbers in the milk and placental membranes of infected cows, sheep and goats. Prevention for personnel includes not drinking raw milk and observing good hand washing practices after handling placentas or assisting animals in labor. There are similar risks for sheep and goats. Even though the university swine, beef, and dairy herds are routinely tested for brucellosis, it is advisable to follow safety precautions. The disease in man is disabling; recurrent fevers, infection of the bony spine, scoliosis, and infection of testes.

Q FEVER

A disease of sheep and goats, (but cattle can also be infected) caused by a tiny, rickettsial organism. Placentas and birth fluids contain a high concentration of the infectious agent, as may milk. Avoid direct contact with the placenta or birth fluids of sheep, goats and cattle and if they must be handled, wear gloves and wash hands immediately after. This organism may cause death in humans, although more common are flu-like symptoms. Herds can be tested to see if the rickettsial organism is present.

TETANUS

Caused by a bacteria called Clostridium tetani. The bacteria is found worldwide and is a common inhabitant of the intestinal tract of man and other animals (in other words, it will be found in manure). The infective bacterial spores can remain in soil for many years. Spores usually enter the body through a puncture wound contaminated with soil or manure. However, many human cases have followed injuries considered too trivial for medical attention and in some cases there is absolutely no record of a physical injury or wound. The case fatality ranges from 30-90%. The incubation period is quite varied but averages 3-21 days. A common early sign suggestive of tetanus is abdominal rigidity. Prevention for personnel includes maintaining adequate vaccination and reporting any injury to the unit supervisor.

RABIES

Rabies is universally fatal! Transmission occurs through a bite, scratch or abrasion from an infected animal. Farm animals usually are bitten by a rabid dog, coyote, cat, raccoon, skunk or bat, or an infected herdmate. Rabid animals of all species exhibit signs of central nervous system disturbances once they are past the early incubation stage. Unfortunately, an animal in the first stages of the disease may show no signs at all and yet still be infective. Sometimes, infected horses bite other animals or people at the slightest provocation and some infected cattle will butt objects or act like they have something caught in their throat. Report all animals showing central nervous symptoms to the Farm Animal Veterinarian and the unit supervisor, and do not attempt to handle this animal!  Report any bite wound or scratch to the unit supervisor. Should rabies be suspected, the animal will be quarantined and tests completed to determine if the animal has the disease.

TUBERCULOSIS

A bacterial disease which can be spread from cattle to man and also from man to cattle! The infection may be limited to pulmonary symptoms, or because the bacteria is spread in the bloodstream, it may affect virtually any body system. Transmission is mainly by inhalation, although man can become infected by drinking raw milk from infected cattle. Cattle are tested for the bacteria by using a skin test very similar to the one administered to humans. Although the disease was on the decline in America, the influx of immigrants from other countries and poor utilization of public health clinics has resulted in a dramatic increase in cases of human tuberculosis. The disease occurs throughout the world and in many nations, including Mexico, infection of man and livestock is widespread. Of special risk to the university cattle are visitors (school children), university students and employees who may be positive for this disease.

CRYPTOSPORIDIUM

A tiny, one-celled parasite which invades the intestinal epithelium of many different species of animals and birds. Most normal, healthy individuals exposed to this parasite never show clinical symptoms but severe diarrhea may occur in the very young, the very old and those individuals which are sick or stressed. When severe diarrhea occurs, dehydration, weakness, collapse and death may occur. Treatment is aimed at moderating the symptoms and may or may not be effective-at this time, there is not a specific, effective treatment for this parasite. Because the parasite can infect so many different species and survive for long periods of time outside the body in a cool and moist environment, control consists of isolating animals with diarrhea and observing good hand washing practices after handling infective animals or cleaning their pens.

TOXOPLASMOSIS

Caused by a tiny, one celled parasite which can infect virtually all warm-blooded species and spread throughout the tissues of the body. The greatest threat is to pregnant females (women and other animals), since infection of the fetus may lead to abortion or severe birth defects. Many people and animals are infected at some time in their life but show no clinical disease and the organism stays dormant in body tissues. Thus, the cycle of infection is interrupted, unless another animal eats the body tissues containing these dormant organisms (if meat is properly cooked, the dormant organism in the tissues will not survive and is no longer infective). The parasite behaves in a different fashion in members of the cat family where the parasite multiplies in the intestinal wall and is shed in large numbers in the feces. Should the cat defecate near food or water, the animal which ingests the contaminated food or water may become infected. Infections of small children sometimes occur when they play in sandboxes in which an infected cat has defecated. To prevent infection, people should only eat fully cooked meat and observe good hand washing procedures, particularly after changing litter boxes of cats. For livestock and horses, it is important to protect food and water from fecal contamination from cats; stray cats should be removed from the property. Should any animal abort, one should wear gloves to handle the placenta and aborted tissues and be certain to wash hands thoroughly after removing the gloves.

CAMPYLOBACTER

Campylobacteriosis (vibriosis) is due to several Campylobacter sp. known to cause disease. In cattle and sheep, Campylobacter fetus is relatively common and causes infertility, abortion and weak or dead newborn calves and lambs. Other Campylobacter species (C. jejuni, C. hyointestinalis ) can induce intestinal disease in many animals, including humans. People can become infected by contact with infected animals, by eating contaminated food or water, or by handling infected placentas. Should any animal abort, one should wear gloves to handle the placenta and aborted tissues and be certain to wash hands thoroughly after removing the gloves. The infection in people causes severe diarrhea, abdominal pain, fever, nausea and vomiting but complications may include arthritis, convulsions and meningitis. There has been one case of a university farm worker being infected with this bacteria within the past few years. In cattle, Campylobacter fetus is transmitted by sexual contact and bulls and cows which are "carriers" can lack symptoms but still spread the disease. The preputial secretions from bulls and the vaginal mucus of cows can be cultured to see if the bacteria is present; herd health programs should require all animals to be tested before they are introduced to the herd.

LEPTOSPIROSIS

A bacteria which may be transmitted to humans by the urine of infected animals of all species. The organism may also enter through minor skin lesions and via the conjunctiva. In cattle, fever and loss of appetite occur with rapid decline in milk yield and mastitis. Pregnant cows abort. The disease in man ranges from inapparent infection to severe infection and death. Prevention includes early detection of the disease in the animals and personnel observing proper handwashing procedures.

COLIBACILLOSIS

Some Escherichia coli (E. coli) strains are species-specific, others are not. The bacteria is shed in large numbers in the feces and humans may become infected by not washing hands well after handling manure from infected animals. Humans may also become infected by handling animal carcasses or meat which has been contaminated by feces. Raw milk and undercooked meat products can also contain pathogenic strains. In humans, the enterotoxigenic strains may cause profuse and watery diarrhea, abdominal colic, vomiting, dehydration and death. Calf diarrhea due to E. coli is a disease causing mortality in calves less than 10 days old. It causes serious diarrhea, with whitish feces and rapid dehydration. Mastitis caused by E. coli occurs most often in older cows with dilated milk ducts. In the horse, perhaps 1% of abortions and 5% of deaths of newborns were due to E. coli.

Prevention for humans includes: good hand washing procedures, not drinking raw milk or eating undercooked meat.


The Iowa State University Center for Food Safety and Public Health (CFSPH) is an excellent resource for disease agents that threaten food production or public health. Additional information about the diseases described above plus facts about other zoonotic diseases can be found on the Zoonotic Disease Fast Facts section of the Iowa State CFSPH website.

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