Mycobacteria

Question 1

Described the general characteristics for Mycobacteria.

Answer 1

These bacteria are acid-fast, non motile, rods that do not produce spores or demonstrable capsules. Soft and pliable because they do not posses a cell wall.

They are aerobic but some grow better in the presence of CO2.

Pathogens vary in size from 1-3 μm by .2-.6 μm and may have a beaded appearance (extremely small…just like my attention span during micro lecture)

Question 2

Why are Mycobacteria acid fast stained?

Which species is only partially acid fast stained?

Answer 2

Due to the high lipid content (mycolic acids) of their cell walls plus these mycolic acids have a longer carbon chain length (50 to 90 carbon atoms).

The acid-fast stain is an important characteristic of the mycobacteria.

Nocardia asteriodes

Question 3

Label the following membrane components of Mycobacteria.

Answer 3

1. ) Mycolic acid
2. ) Porin
3. ) glycolipid
4. ) free lipid

Question 4

In general, what is the growth of Mycobacteria?

A rapidly growing Mycobacteria is usually associated with what?

Answer 4

These pathogens grow slowly.

The generation time (doubling time) can vary from 30 minutes to 2 hours and even up to 6 hours.

Rapidly growing Mycobacteria usually correlates with the non-pathogenic species (with some exceptions).

Question 5

What is the media you use to grow Mycobacteria?

How long is the shelf life for these media?

Answer 5

Many of these are egg-based media (need moist, rich media). So they are quite different from the commonly used culture media because of the length of time required for growth.

These media have a long shelf life and are capable of being incubated several weeks without drying or deterioration.

Question 6

What do typical Mycobacteria colonies look like?

Answer 6

Picture of Mycobacterium tuberculosis.

Question 7

What is the typical habitat for Mycobacteria?

What were the most likely ancestors for Mycobacteria?

Answer 7

Habitat in healthy animals: mucous membrane.

Habitat in diseased animals: Lungs, conjunctiva, mammary glands, joints, serosal joints (occasionally urethra and brain).

Clostridial organisms.

Question 8

What is the purpose of Mycobacteria having a high lipid content?

What is the specific component attributing to the high lipid content?

Answer 8

It is more hydrophobic it is more likely to be taken up by macrophages (these organisms like to grow inside of macrophages).

Mycolic acid

Question 9

How resistant are mycobacteria to disinfectants?

What disinfectants are they susceptible to?

What attributes to their resistance?

Answer 9

• They are very resistant to halogen and quaternary ammonium disinfectants.
• They are killed by phenol and substituted cresylic compounds.
• The marked resistance to disinfectants such as chlorine and iodine is due in part to the presence of lipids in the cell walls.

Question 10

Where do Mycobacteria like to replicate?

Answer 10

Mycobacteria are facultative intracellular parasites (at least one is an obligate intracellular parasite) that are very efficient at surviving within phagocytic cells (primarily macrophages).

Saprophytic mycobacteria are usually killed by phagocytic cells but pathogenic mycobacteria multiply and eventually lyse the phagolysosome.

Question 11

How does Mycobacteria infect tissue and what are the types of lesions you see with Mycobacteria?

Answer 11

The mycobacteria are found free in the cytoplasm of the macrophage eventually rupturing it.

Adjoining cells are infected and this process eventually leads to the formation of collections of granulomatous tissue that form tubercles.

Question 12

How is the infection of macrophages part of the disease process for Mycobacteria?

Answer 12

Macrophages allow for an efficient method of dispersal. These lesions can form anywhere in the body (disseminated disease) but are often localized in the lungs, spleen, or liver.

In humans, infection of the larynx, kidneys, vertebral column and other sites is seen

Question 13

What are the 5 mechanisms of bacterial resistance for Mycobacteria?

Note: A wide variety of mechanisms to explain the resistance of mycobacteria to killing have been proposed. Most of them have not been proven to play a definite role.

Answer 13

1. ) Cord factor
2. ) Phospholipids
3. ) Glycolipids
4. ) Fatty acids
5. ) Sulfur-containing glycolipids (Sulfolipids)

(Some of these you will need to know in more detail)

Question 14

Explain the “cord factor” of bacterial resistance for Mycobacteria.

Answer 14

Trehalose 6-6’ dimycolate is present in all strains of pathogenic mycobacteria and also in some saprophytes.

Influences immune responses and granuloma formation

Question 15

What is this picture showing?

Answer 15

A tubercle

Question 16

What is the purpose of the Sulfur-containing glycolipids (Sulfolipids) in Mycobacteria.

Answer 16

They are believed to alter killing by host macrophages by one of the following mechanisms:

1. ) May interfere with attachment of the lysosome to the phagosome.
2. ) Prevent release of the lysosomal enzymes into the phagosome.
3. ) May inactivate lysosomal enzymes.
4. ) Pathogens may utilize the lysosomal enzymes for energy.
5. ) Pathogens seem to be able to resist toxic oxygen metabolites (superoxide anion) because they produce superoxide dismutase.

Question 17

What type of immune response do you see with a mycobacteria infection?

Answer 17

The immune response to the mycobacteria is largely cellular and almost entirely mediated by macrophages. Lymphocytes are known to release soluble mediators which potentiate the action of the macrophages in killing mycobacteria.

The humoral immune response is not considered to be important.

Note: With some mycobacteria it has been demonstrated that reactive nitrogen intermediates play an important role in killing in combination with the reactive oxygen intermediates.

Question 18

True/False: Mycobacteria are potent adjuvants.

What does that mean in terms of the cell mediated immune response?

Answer 18

TRUE

Mycobacteria are unique in that killed bacteria are capable of inducing a cell-mediated immune response.

When killed mycobacteria are added to mineral oil, a strong immune response can be induced.

Freund’s complete adjuvant is such a material. It usually contains killed Mycobacterium smegmatis or M. phlei (non pathogens). These adjuvants are not used commercially because of lesion development at the injection site and even their use for research purposes is controlled.

Question 19

Describe “Freund’s complete adjuvant”.

Are these commercially used?

Answer 19

When killed mycobacteria are added to mineral oil, a strong immune response can be induced. It usually contains killed Mycobacterium smegmatis or M. phlei (non pathogens).

These adjuvants are not used commercially because of lesion development at the injection site and even their use for research purposes is controlled.

Question 20

Describe how you would diagnose a Mycobacteria infection.

Answer 20

Mycobacteria usually induce delayed-type hypersensitivity (DTH) 4 to 8 weeks following infection.

The DTH reaction (intradermal skin test) is useful as a diagnostic test for exposure to tubercle bacilli. The antigen used to induce a DTH reaction is referred to as tuberculin.

Question 21

What are the two most common types of tuberculin tests?

Which one is the “standard”?

Answer 21

There are several different kinds of tuberculins but the two most common are:

OT: Old Tuberculins

PPD: Purified Protein Derivative

PPD tuberculins are the standard

Question 22

Describe the OT (Old Tuberculin test) for Mycobacteria.

Answer 22

This material is less purified than the PPD tuberculins and thus it presents problems with nonspecific reactions in cattle.

This material is used for tuberculin testing in the eyelid of non-human primates.

Advantages: producing pronounced swelling of the eyelid that does not require handling of the animal to read the test.

Question 23

Describe the PPD (Purified Protein Derivative) tuberculin test.

Answer 23

These are prepared by growing the organism on synthetic culture media, autoclaving, removing the cells and precipitating the proteins with either ammonium sulfate or TCA (trichloroacetic acid).

The material is then assayed for protein content and biological activity. This allows one batch of PPD to be compared to another for purposes of standardizing the material.

The majority of the tuberculins used are PPD’s.

Question 24

What is the antibiotic susceptibility of Mycobacteria?

Answer 24

The drugs used to treat infections usually include isoniazid and rifampin. The development of drug-resistant strains has become an important problem in human medicine.

Question 25

Mycobacteria tuberculosis

This is the principal cause of tuberculosis in what species?

How are primates infected?

What other animals can it infect?

Answer 25

• Humans and other primates.
• Infection in primates is usually due to contact with infected humans.
• The organism is an occasional cause of tuberculosis in dogs and pigs (also elephants).

Note: The incidence of tuberculosis in third world countries is on the rise due to the influence of AIDS and other factors

Question 26

M. tuberculosis

How many people die per year of M. tuberculosis?

How many new cases occur worldwide every year?

How many people are estimated to have a latent infection of M. tuberculosis?

Answer 26

• it is estimated that 1.7 million people die per year worldwide
• 9.2 million new cases occur.
• Approximately 2 billion people are thought to have latent infections.

Question 27

Describe the disease process of M. tuberculosis in humans.

Answer 27

It is thought that most humans are relatively resistant to the development of progressive tuberculosis and that only about 1 in 10 actually develop disease.

In humans, tuberculosis is most often pulmonary in nature.

Large lung lesions can develop and progress to the point that large blood vessels are compromised and the patient can bleed to death quickly.

Tuberculous lesions occur in the vertebral column, kidneys, bladder, larynx and at other sites.

Question 28

What is this?

Answer 28

M. tuberculosis in the lungs of a human.

Question 29

What is this?

Answer 29

M. tuberculosis infection in the kidney of a human.

Question 30

What is the standard treatment for Mycobacterium tuberculosis?

Answer 30

Standard anti-TB therapy typically continues for six months and requires patients to take about one-third kilogram of a mixture of anti-TB drugs when administered daily.

Oddly enough, this is termed the Ashort course of anti-TB therapy.

Question 31

Which cells do the anti TB (in this case M. tuberculosis) target?

Answer 31

So the organisms present in tubercles may be growing rapidly, slowly or be dormant.

The easiest to kill are the ones that are growing relatively rapidly.

That is why there is an extended therapeutic regiment in order to kill the persistent, non-growing or very slowly growing bacilli.

Question 32

Due to the prolonged treatment (6 mo) for M. tuberculosis, what problems have arisen because of this?

Answer 32

In the US and other developed countries, it has been difficult to maintain this extensive treatment regimen among the homeless population, and other groups such as addicts.

This has led to the development of drug-resistant M. tuberculosis.

Extensive drug resistant tuberculosis (XDR-TB) is surging due to problems with treatment. In developed countries, removal of a lung may be recommended to get an infection under control.

Question 33

What is the most widely used human immunizing agent for M. tuberculosis?

Is it approved for use in the US? Why?

Answer 33

Bacille Calmette Guerin (BCG)

It is a Aweakened live strain of Mycobacterium bovis that was developed in the 1930’s and it remains the only immunizing product against tuberculosis.

It is used in many other countries, however, it is not used in the U.S. because of the low incidence of tuberculosis in the population and the fact that it complicates diagnosis (reads a false positive).

Question 34

How effective is the Bacille Calmette Guerin (BCG) in humans?

Answer 34

Immunization is effective in reducing the likelihood and severity of lethal forms of tuberculosis in infants and young children.

In some areas of the world, children are given multiple immunizations with BCG but the best evidence indicates that multiple immunizations are not necessarily more protective.

Also, protection does not extend into adulthood and some countries that use BCG have one-third of their adult populations infected with M. tuberculosis.

Question 35

Why is the BCG immunization against M. tuberculosis not used in the US?

What test must be performed to identify a true positive?

Answer 35

Immunization complicates diagnosis via the tuberculin skin test because immunized individuals react to PPD tuberculins. These false positive reactions seem to be more of a problem when children are given multiple doses of BCG.

When individuals immigrate to the U.S. (or come as graduate students, etc.) from areas where BCG is used, a positive skin test is considered positive despite a history of immunization.

An ELISA or other tests must be performed to identify true positive individuals.

Question 36

Mycobacterium bovis

What animals is it able to infect?

Is it able to cause disease in birds?

Answer 36

This organism causes tuberculosis in cattle, pigs, cats, horses, primates, dogs, sheep, and goats.

It does not cause disease in birds.

Question 37

Describe what the colonies and growth of Mycobacterium bovis.

What must NOT be added to the culture media?

Answer 37

Primary cultures usually take 3 to 4 weeks before colonies can be detected. The colonies are rough and waxy on agar media.

Glycerol is inhibitory to the growth of the organism and therefore must not be added to the culture medium. This is a problem when cultures are submitted to a lab doing cultures of human mycobacteria because glycerol is routinely added to the media.

Question 38

True/False: Mycobacterium bovis is susceptible to pasterization and sunlight.

Answer 38

TRUE

Question 39

How prevalent is M. bovis?

How effective have eradication programs been?

Have there been any setbacks?

Answer 39

The organism is present in cattle populations worldwide.

Prior to initiation of the eradication program, the infection rate was greater than 15 percent in many areas of the U.S. In the U.S. and other countries where eradication programs have been successful, the incidence of infection is very low.

However, recent problems with wild white-tailed deer in Michigan and other states and farmed elk in several states have caused setbacks to the eradication program.

Question 40

How is M. bovis spread throughout individuals?

Answer 40

Transmission is principally via the respiratory route.

A small proportion of infections occur through ingestion of milk, congenitally and, possibly, venereally.

Question 41

Describe the pathogenesis of M. bovis starting with inhalation of the organism.

(it is a long process)

Answer 41

• Following inhalation the organism is ingested by pulmonary macrophages.
• The organism grows in the macrophage, eventually killing it and lysing the cell.
• Other macrophages ingest the organisms and are eventually killed.
• Tubercles consisting of the organism, macrophages, giant cells, and other inflammatory cells form, enlarge, and may develop a necrotic center.
• The lesions become encapsulated.
• The organism may disseminate via the lymph and form tubercles in the lymph nodes and at sites of secondary metastasis such as the liver and spleen.
• Animals that do not mount a protective immune response develop generalized tuberculosis with wasting and death.

Question 42

This is from a cow. What organism would be at the top of your differential list?

Answer 42

Mycobacterium bovis

Question 43

How long post infection does it take for a CMI response in M. bovis?

Is the M. bovis completely cleared?

Answer 43

CMI responses become effective about 4 weeks following infection leading to enhanced phagocytosis and killing of the organism.

The infection may be slowed or halted but the organism is often not completely cleared. Reactivation of the infection and shedding of the organism may occur.

Note: T-lymphocytes remain sensitized to the organism for life.

Question 44

How would you diagnose M. bovis?

Answer 44

Delayed type hypersensitivity (skin test) with PPD tuberculin is the standard in-field test performed by veterinarians.

State veterinarians re-test positive animals with a comparative cervical (DTH test in the skin of the neck) using positive and negative control PPD=s) Positive animals on the comparative cervical test are sent to postmortem for examination and culture of lesions.

Question 45

What does Mycobacterium avium (MAIS) Complex stand for?

What is the natural habitat for MAIS?

Answer 45

The term MAIS complex refers to a group of organisms formerly classified as separate genera: M. avium, M. intracellulare and M. scrofulaceum.

Found in soil, bird intestines (causes a majority of tuberculosis in swine)

Question 46

Mycobacterium avium (MAIS) Complex

What animals do they typically infect?

How easy are they to treat?

Answer 46

Members of this group are responsible for the majority of tuberculosis in avian species and swine.

Organisms in this group are highly resistant to many of the commonly used antimycobacterial drugs. Thus they are difficult to treat.

Treatment is usually only attempted in humans. Infectivity of the members of this group for humans is relatively low, but the disease is progressive and often refractory to treatment (see in AIDS patients).

Question 47

How many serotypes of Mycobacterium avium (MAIS) are there?

Which species are they the most virulent?

Answer 47

There are many serotypes.

Serotypes 1, 2 and 3

These serotypes are generally more virulent for birds but can produce disease in swine and other animals

Question 48

How are the different serotypes of M. avium (MAIS) transmitted?

Answer 48

Transmitted by ingestion of contaminated feces or soil in which the organisms survive for long periods of time.

Question 49

What is the pathogenesis for serotypes 1, 2 and 3 in M. avium (MAIS)?

Answer 49

Lesions develop slowly and are usually not observed in birds less than 1 year of age.

The lesions can be quite disseminated and involve bones, joints, liver, spleen, and the intestinal tract.

Lesions in the intestinal tract may appear as nodules that open and discharge into the lumen of the intestine.

This accounts for the large numbers of organisms that may be found in the feces and thus for the mode of transmission.

Question 50

What are the serotypes of M. avium (MAIS) that most commonly cause disease in swine?

Where are the lesions predominately located?

How is this organism transmitted between individuals?

Answer 50

Serotypes 1, 2, 4 and 8

Lesions often appear as foci in the mandibular and mesenteric lymph nodes and occasionally in the intestinal tract. Lesions can occur in the liver and elsewhere.

The organisms are transmitted by ingestion.

Note: Certain serotypes are becoming increasingly common in humans infected with the AIDS virus.

Question 51

This is from a bird. What is your top differential?

Answer 51

M. avium (MAIS)

Question 52

This is a liver from a bird. What is your top differential?

Answer 52

M. avium (MAIS)

Question 53

What organism causes leprosy in humans and armadilos?

Is this disease common around the world and in the United States?

Answer 53

Mycobacterium leprae

Some areas of the world still have a fairly high incidence of leprosy. The disease is not a problem in the U.S. presumably because of diet and environmental conditions.

Question 54

What disease is this?

Answer 54

M. leprae

Question 55

M. leprae

What animal naturally harbors this organism systemically?

Before this animal (in the question above) was discovered to harbor M. leprae naturally, what did scientists have to use instead?

What is the generation time of this organism?

Where, in humans, does this organism tend to be found during disease?

Answer 55

• Armadillos are known to carry the organism and it has been isolated from them in Texas and Louisiana. Armadillos have proven to be very useful in studying the organism.
• Earlier studies were limited to work in foot pads of mice.
• The organism grows very slowly and has a generation time of 20 to 30 days or more.
• In humans the organism is confined mainly to the skin, and peripheral nerves whereas it can be found systemically in armadillos.

Question 56

Mycobacterium lepraemurium

What animal(s) does this organism infect and what type of disease does it produce?

What is its growth on culture?

Answer 56

This organism produces an infrequently reported leprosy-like disease in cats and rats.

It grows very slowly on laboratory media at 30 C on primary culture.

Question 57

Mycobacterium marinum

What animal(s) does this organism infect and what type of disease does it produce?

What is its growth on culture?

Answer 57

This organism produces “swimming pool granuloma” on the arms and legs of humans and granulomatous lesions in cold-blooded animals.

Typical lesions in humans involve trauma to an extremity in contact with water and the development of a single granulomatous lesion.

The organism grows only at 30 C and produces a yellow pigment when grown in the presence of light (photochromogenic).

Question 58

What is this image depicting?

What species of Mycobacterium exhibit this on culture?

Answer 58

Photochromogenic Mycobacterium (yellow pigment produced by colonies when grown in the presence of light)

• M. kansasii*
• M. marinum*

Question 59

Mycobacterium kansasii

What animal(s) does this organism infect and what type of disease does it produce?

What other organism looks very similar to M. kansasii that makes it hard to distinguish?

How does this organism grow on culture?

Answer 59

• Cause of lymph node lesions in cattle, deer and swine and both pulmonary and extrapulmonary lesions in humans.
• The infections are difficult to distinguish from M. bovis infections in cattle.
• The organism is a slow grower (3-7 weeks on primary isolation) and is photochromogenic.

Question 60

Mycobacterium fortuitum

What animal(s) does this organism infect and what type of disease does it produce?

How does it grow on culture?

Answer 60

Produces pulmonary disease in dogs and humans (usually immunosuppressed).

This organism grows rapidly compared to other mycobacteria (fast grower).

Question 61

Mycobacterium chelonae

What animal(s) does this organism infect and what type of disease does it produce?

How does it grow on culture?

Answer 61

Observed in swine lymph node lesions and cold-blooded animals; reported to be isolated from patients receiving porcine heart valve transplants.

This organism is a fast grower.

Question 62

Mycobacterium avium subspecies paratuberculosis

What disease is associated with this organism?

What species does it affect?

What human disease has it been associated with (although controversial)?

Answer 62

• This organism is the cause of Johne’s disease (a chronic enteritis)
• Cattle, sheep, goats, camels, llamas, and some wild ruminants.
• It has also been linked to Crohn’s disease in humans but this is controversial at best and not supported by a vast majority of the work.

Question 63

Mycobacterium. avium subspecies paratuberculosis

What is the morphology of this organism?

Answer 63

Considerably smaller than the tubercle bacilli. The organism is a short rod approximately 1.0 μm in length. In tissues and feces the organism commonly occurs in clumps.

Hard to see but they are the pink rods in the picture.

Question 64

Mycobacterium avium subspecies paratuberculosis

What is the growth of this organism on culture?

What special considerations need to be taken when trying to grow M. paratuberculosis?

Answer 64

Primary cultures grow very slowly and require up to 4 to 16 weeks or more.

1. An iron chelating compound (mycobactin) is required for primary isolation (mycobactin dependence).
2. Because the specimens for culture of M. paratuberculosis are usually intestinal or fecal, specimens must be treated to control contaminating bacteria that overgrow the cultures.

Question 65

M. paratuberculosis

What is the resistance of this organism?

What is the distribution of this organism and what species of animal(s) can it infect?

Answer 65

Resistance: The organism will remain viable in feces and soil for up to 8 to 9 months. It is killed by moderate heat, 5% formalin, or 5% phenol

Distribution: The disease is widespread in the U.S. in cattle. It was traditionally thought to be a problem only in dairy cows but it is now recognized as a major problem in beef cows. It is enzootic throughout the world. All breeds of cattle are susceptible. The disease is being increasingly recognized as a problem in sheep and goats. Infection can be a difficult problem in captive ruminants.

Question 66

M. paratuberculosis

How is this organism transmitted?

Which age group of cows is most susceptible?

What factors determine which animals show clinical disease?

Answer 66

• Large numbers of organisms are often shed in the feces and the organism is transmitted by ingestion. Relatively high rate of transplacental transmission. In-utero transmission is known to occur at a rate from 8 to 37%.
• Young animals are more susceptible to infection. Cattle infected as adults are usually resistant to development of clinical disease.
• Most cases of clinical disease develop in young cows, with disease often becoming apparent during the early part of the first or second lactation. High producing cows seem to be more susceptible. Beef cows and bulls that are stressed may also develop clinical disease.

Question 67

M. paratuberculosis

Describe the pathogenesis of Johne’s disease once the organism is ingested.

Answer 67

• Once ingested, the organism penetrates the epithelium of the ileum and colon and is phagocytosed by macrophages.
• The organism is not enclosed within a phagosome as are the tubercle bacilli.
• The organism multiplies in the macrophages and stimulates a granulomatous response that can eventually spread throughout the intestine and regional lymph nodes.
• The intestine can become very thickened due to the proliferation of great masses of epithelioid cells.

Question 68

M. paratuberculosis

What are the clinical manifestations of Johne’s disease?

Answer 68

IT VARIES!

• Clinical disease in cattle is chronic and characterized by intermittent diarrhea and emaciation.
• Many animals have remissions and exacerbations of the disease until they die or are culled.
• In other animals, there may be emaciation with little or no diarrhea.
• Other animals may remain infected for long periods and remain relatively healthy.

Question 69

M. paratuberculosis

How would you go about diagnosing an animal suspected of having Johne’s disease?

What are some of the various diagnostic tests you could do?

Answer 69

Bacteriological and immunological methods have high error rates when testing animals in early-stage disease making diagnosis difficult. Diagnosis is easier once cattle develop clinical signs and are shedding large numbers of organisms.

1. Culture
2. PCR
3. Acid fast stain
4. Serologic responses
5. A delayed type hypersensitivity (DTH) test

Question 70

M. paratuberculosis

Which test is a definitive means of diagnosing M. paratuberulosis?

Is it commonly used? Why or why not?

What have been some recent developments for this test to make it more efficient?

Answer 70

Culture method

It is less commonly done because it can take several weeks ( 6 to 16 or more).

Recent developments in liquid culture methods have increased the sensitivity of this method and decreased the time necessary for growth but it is still a lengthy process. Liquid culture is the only culture method that works well for sheep isolates.

Question 71

M. paratuberculosis

The “real-time quantitative PCR” method used primarily to identify which type of animals? How sensitive is this test?

What test has PCR come to replace in diagnostic labs?

Answer 71

It is used on feces and is highly sensitive especially for animals that are moderate to high shedders of the organism. With light shedders, the test is about 75% sensitive.

Note: With light shedders, there can be a high rate of disagreement between culture and PCR.

The culture test.

Question 72

M. paratuberculosis

Describe the acid fast stain method as a way to identify M. paratuberculosis.

What is the best tissue to sample?

Answer 72

Microscopic examination of fecal or mucosal smears stained with Ziehl-Neelsen acid fast stain reveal clumps of bacilli.

The best tissues for diagnosis are the ileo-cecal valve and adjacent lymph nodes.

Question 73

M. paratuberculosis

When are serologic response tests most effective in identifying M. paratuberculosis?

Which tests are more widely used than the serologic reponse tests?

Answer 73

Serologic responses usually do not develop until clinical disease is evident.

Complement fixation, ELISAs, and agar gel immunodiffusion tests are the most widely used serologic tests.

Question 74

M. paratuberculosis

A delayed type hypersensitivity (DTH) test uses what specifically?

What is the best type of test for detecting infected animals?

Answer 74

This test uses johnin (produced from culture filtrates of M. paratuberculosis).

Recent work has led to improved DTH test reagents but the work has not proceeded. Some type of cell-mediated immunity assay may ultimately be the best type of test for detecting infected animals.

Question 75

What is the treatment for M. paratuberculosis?

Answer 75

Treatment of the disease is not recommended.

Why?

Scientific review and a case study show that therapy for M. paratuberculosis in cattle produces only remission of clinical signs and does not eliminate the infection.

In addition, therapy was costly, inconvenient since it requires daily medication and, once treatment stopped, the signs of the infection returned since the infection was not cured.

Basically the best treatment is prevention!

Question 76

Is there a vaccination for M. paratuberculosis for cattle?

Is it effective?

What happens if a human were to accidentally innoculate themselves?

Answer 76

• There is a vaccination and is used in herds where infection persists. The product used is a killed M. avium subspecies paratuberculosis (bacterin) preparation.
• The most recent evidence indicates that the bacterin may markedly decrease the shedding rate but does not prevent infection. It is more commonly used in dairy calves
• It produces severe tissue responses if accidentally inoculated into humans.

Question 77

What is the purpsoe of the Voluntary Johne=s Disease Control Program?

Answer 77

The US has a voluntary program in place for controlling (not eradicating) Johne’s disease.

This program is primarily designed to decrease transmission of the organism to calves in order to lessen the economic impact of Johne’s.

USDA funding for this program was drastically reduced and the cost of testing is now the responsibility of the herd owners

Question 78

This animal presented with chronic and intermittent diarrhea and emaciation.

What should be on your top differential?

Answer 78

M. avium subspecies paratuberculosis

Question 79

This animal presented with chronic and intermittent diarrhea and emaciation.

Note the marked thickening of the small intestine.

What should be at the top of your differential list?

Answer 79

M. avium subspecies paratuberculosis