VETERINARY MICROBIOLOGY

Veterinary microbiology is concerned with the microorganisms, both beneficial and disease causing, to non-human animal life. For a small animal veterinarian, the typical animals of concern are domesticated animals, such as dogs, cats, birds, fish, and reptiles. Large animal veterinarians focus on animals of economic importance, such as horses, cows, sheep, and poultry.

The dogs and cats that are such a familiar part of the household environment are subject to a variety of microbiological origin ailments. As with humans, vaccination of young dogs and cats is a wise precaution to avoid microbiological diseases later in life.

Cats can be infected by a number of viruses and bacteria that cause respiratory tract infections. For example the bacterium Bordetella pertussis, the common cause of kennel cough in dogs, also infects cats, causing the same persistent cough. Another bacteria called Chlamydia causes another respiratory disease, although most of the symptoms are apparent in the eyes. Inflammation of the mucous covering of the eyelids (conjunctivitis) can be so severe that the eyes swell shut.

Cats are prone to viral infections. Coronavirus is common in environments such as animal shelters, where numbers of cats live in close quarters. The virus causes an infection of the intestinal tract. Feline panleukopenia is a very contagious viral disease that causes a malaise and a decrease in the number of white blood cells. The immune disruption can leave the cat vulnerable to other infections and can be lethal. Fortunately, a protective vaccine exists. Like humans, cats are also prone to herpes virus infections. In cats the infection is in the respiratory tract and eyes. Severe infections can produce blindness. Another respiratory disease, reminiscent of a cold in humans, is caused by a calicivirus. Pneumonia can develop and is frequently lethal. Finally the feline leukemia virus causes cancer of the blood. The highly contagious nature of this virus makes vaccination prudent for young kittens.

Dogs are likewise susceptible to bacterial and viral infections. A virus known as parainfluenzae virus also causes kennel cough. Dogs are also susceptible to coronavirus. Members of the bacterial genus called Leptospira can infect the kidneys. This infection can be passed to humans and to other animals. A very contagious viral infection, which typically accompanies bacterial infections, is called canine distemper. Distemper attacks many organs in the body and can leave the survivor permanently disabled. A vaccine against distemper exists, but must be administered periodically throughout the dog's life to maintain the protection. Another virus called parvovirus produces a highly contagious, often fatal, infection. Once again, vaccination needs to be at regular (usually yearly) intervals. Like humans, dogs are susceptible to hepatitis, a destructive viral disease of the liver. In dogs that have not been vaccinated, the liver infection can be debilitating. Finally, dogs are also susceptible to the viral agent of rabies. The virus, often passed to the dog via the bite of another rabid animal, can in turn be passed onto humans. Fortunately again, vaccination can eliminated the risk of acquiring rabies.

Microbiological infections of farm animals and poultry is common. For example, studies have shown that well over half the poultry entering processing plants are infected with the bacterium Campylobacter jejuni. Infection with members of the bacterial genus Salmonella are almost as common. Fecal contamination of poultry held in close quarters is responsible. Similarly the intestinal bacterium Escherichia coli is spread from bird to bird. Improper processing can pass on these bacteria to humans, where they cause intestinal maladies.

Chickens and turkeys are also susceptible to a bacterial respiratory disease caused by Mycoplasma spp. The "air sac disease" causes lethargy, weight loss, and decreased egg production. Poultry can also acquire a form of cholera, which is caused by Pasteurella multocida. Examples of some other bacteria of note in poultry are species of Clostridium (intestinal tract infection and destruction of tissue), Salmonella pullorum (intestinal infection that disseminates widely throughout the body), Salmonella gallinarum (typhoid), and Clostridium botulinum (botulism).

Cattle and sheep are also susceptible to microbiological ailments. Foot and mouth disease is a prominent example. This contagious and fatal disease can sweep through cattle and sheep populations, causing financial ruin for ranchers. Moreover, there is now evidence that bovine spongiform encephalopathy, a disease caused by an infectious agent termed a prion, may be transmissible to humans, where it is manifest as the always lethal brain deterioration called Creutzfeld-Jacob disease.