Dr. James Evermann
Lecture 5: Infectious Organisms Continued
Infectious Bacterial Agents Continued:
Intracellular bacteria replicate inside cells. It is very important to recognize those agents that replicate inside cells versus those that replicate outside cells. Antibodies do not control intracellular bacteria. Intracellular bacteria are killed by T cytotoxic cells or killer T-cells. Intracellular bacteria are not commonly controlled by antibodies, therefore it requires a living bacteria to stimulate the proper immune response. Most bacteria used to make vaccines are killed. Now the predominant thing to notice is that they cause abortion. To stimulate a proper immune response against intracellular bacteria requires a vaccine containing live bacteria.
Brucella species
Mycobacterium species
Actinomyces species
Borrelia burgdorferi
Borrelia burgdorferi is the agent that causes Lyme disease. The agent is spread primarily by deer ticks. Horses, dogs, and humans can be infected by this bacterium. Would you consider this a zoonotic infection? Think about it. The tick spreads the organism but cattle, horses, and dogs, don’t spread it to humans. One could argue whether or not it is zoonotic. There has been no definitive evidence to show that a cow infected with Lyme disease can transmit it to a human even if there are ticks on the premises.
Serpolina
innocens causes Hairy Foot Warts in cattle. The name is a little misleading because initially it was thought not to
cause disease and that is why it was given the name "innocens".
Leptospira spp.
Leptospira infections are a real challenge because they infect a wide
range of hosts.
Whenever an agent infects multiple hosts the infection is very difficult
to control. Leptospira can cause a fatal liver infection. The usual way
in which the bacteria are acquired is via the eye. The agent is spread primarily
in urine.
It enters the water source, and then it is spread to susceptible species.
Leptospira are zoonotic. There is a
vaccine but it is not very effective.
L. bratislava causes Moon Blindness in horses. There are Leptospira bacterins. The bacterin contains five different leptospira. The bad news is that they are not very effective. Vaccines do not prevent carriers. If you are in an irrigated area such as the Columbia basin, you are probably going to have to vaccinate three to four times a year. The reason multiple vaccines are required is two fold: it is not a very effective vaccine and there is a lot of water borne contamination.
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Protozoa
Protoza are obligate intracellular parasites. Intracellular parasites
persist in body tissues and control is difficult. Toxoplasmosis (Toxoplasma gondii)
is commonly spread and carried
by cats. It is shed in the feces. Sheep and goats are unusually susceptible to
toxoplasmosis. Signs include abortion or neurologic disease caused by brain
lesions. You rarely
see signs in cats. Cats act as a carrier. They are usually subclinical. Children can become infected
readily with toxoplasmosis. They usually don’t show any
clinical signs. Infection of pregnant women can result in abortion.
Neosporosis is another protozal infection. Neospora canninum is primarily shed from dogs in the feces and is now recognized as one of the leading causes of abortion in dairy cattle.
Trichomoniasis (Trichomonas fetus) is referred to just as "trich" and is a venereal infection. It is carried by bulls and causes infertility. It occurs primarily in beef herds.
Equine protozoal myelitis (EPM) is a relatively new protozoon disease. Cysts develop in the brain and or spinal chord. As the name implies, this is a disease of horses. The intermediate host is the opossum. The disease is primarily seen in Western Washington. We rarely see it in Eastern Washington. The opossum is usually the subclinical carrier. The affected species, horses are accidental or dead-end hosts as affected horses do not shed the protozoan and infect other horses.
These are actually plants, but they act like bacteria.
Mycoplasma are a group of bacteria that have lost their cell walls.
Ureaplasma diversum causes vaginitis, primarily in heifers. Cows build up some resistance to
ureaplasma as they age.
The Rickettsia Group includes Rickettsia, Clamydia, and Ehrlichia.
Three main infections that I want to cover this week are Johne’s, clostridium C and D, and BVD. I want you to pay particular attention because we have carrier animals with two of these, with Johne’s and with BVD. One in particular has been implicated as a cause of chronic ileitis in humans, known as Crohn’s disease. What I am saying is it is implicated. Biopsies of affected tissues show pink bodies that are aggregates of bacteria. There is a statewide initiative to control Johne’s in dairy cows. Johne’s testing will become very, very popular in the near future. This will be part of the herd biosecurity. Any replacements coming into the herd will be tested for Johne’s. You can’t identify carriers unless you test them. Just because they look good doesn’t mean they are not infected.
Johne’s disease causes chronic wasting. The agent multiplies in the tissues, especially in the gut, causing a lack of absorption and nutrition. The animal develops fluid diarrhea and loses condition over 3 to 6 months. During this time Mycobacterium paratuberculosis is shed in feces. Asymptomatic carrier animals shed Mycobacterium paratuberculosis in milk and infect its calves. Then the problem is compounded because organism is shed not only by the cow, but also in the feces of her calves. That is how it is spread on the farm, mother to offspring. These animals grow up with the infection and then they develop disease and lose weight. Control is difficult, and that is why testing of the normal carrier population is really important. When you see a clinically affected animal there is no question of the diagnosis. The carrier animals are the problem.
Clostridium perfringens, type C or D
causes gas filled intestines and hemorrhage. The spores of clostridia look like
tennis rackets. In the laboratory clostridium grows as little plaques on blood agar and causes
hemolysis of the blood in the agar.
BVD is common in the cow
population, both beef and dairy. We commonly vaccinate for it, however it still persists.
This is a virus that infects pregnant animals at 90 to 120 days gestation. The virus infects the calf and the calf looks upon this virus as
"self" and there is no immune response at all to
this virus. That is called tolerance. Tolerance is a really
important concept because that is how the virus can survive in a population of
animals; it neutralizes the immune response through tolerance.
What factors can the rancher control? Cull out carrier animals, but in order to do that you have to test the herd. There is a blood test and testing is recommended for all the replacements coming into the herd. Testing replacements is a form of herd biosecurity. A $3.00 test is well worth its cost because you get rid of the chronic carriers in the herd and get rid of this potentially devastating infection because it is implicated in Crohn’s disease in humans.
How
are you going to control the BVD problem? The key is vaccinating both the
heifers and vaccinate cows pre-breeding to prevent infection between 90 and 120 days of
gestation. That is the key – pre-breeding vaccinations. Additionally checking for
persistent carriers in yearling heifers with a blood test. Calves infected
in utero are born with the cataracts.
BVD also causes
ulceration of the nares, inside the mouth, and on the palate. It
looks like someone took a blowtorch to the mouth, a "burnt muzzle" type of appearance.
Obviously the animal is not going to be eating well.
The lesions start in the mouth and progress down the esophagus,
down into the GI tract, where it causes little pinpoint ulcers. Affected
animal deteriorate much faster than those with Johne's Disease; 4-5 days versus
3-6 months and Johne's animals with clostridial infections progress rapidly;
with in 24 hours.
FAQ:
Question: What are the symptoms of greasy pig disease?
Dr. Evermann: The pig lose their hair and have blotches of oil on their skin.
Questions: Can apple vinegar be used to treat hairy foot warts?
Dr. Evermann: Yes, any kind of foot disinfectant can be used. Vinegar is a weak
solution of acetic acids. You could spray iodine on the feet as
well. Iodine is more effective than vinegar.
Question: How effective is carbon sulfate at treating hairy foot warts?
Dr. Evermann: It is effective but once the bacterium gets into the tissue it is very
difficult to clear up. There is a vaccine for this disease.