This presentation is a comparison between two diseases of cattle which most people never think about or talk about at the same time. However, there are some interesting similarities between Mycobacterium paratuberculosis and Bovine Leukosis (Leukemia) Virus and the diseases they cause, Johne’s Disease and Leukosis (Lymphoma, lymphosarcoma, leukemia) respectively. Perhaps, at present, the most important similarities is the perception that they may both be a public health threat since they both can be found in the meat and milk of infected animals and the prevalence of infection is common especially in dairy cattle. However, it must be emphasized that neither M. paratuberculosis nor Bovine Leukemia Virus has been shown to cause disease in human beings, even when exposure has been extensive (e.g. slaughterhouse workers, veterinarians, researchers working for years with these agents). Nonetheless, "perception seems to be reality" in this day of demands for "zero tolerance" in many products. Furthermore, it would be impossible to establish such tolerance or anything near what is expected. Additionally, these unrealistic expectations are being demanded at a zero cost increase to the consumer.

If we look at the comparison of Johne’s and Leukosis we see the following:

Disease Johne’s (Paratuberculosis) Leukosis (Lymphoma, Leukemia)

Etiologic Agent Mycobacterium paratuberculosis Bovine Leukosis (Leukemia) virus

Agent First Isolated Twort 1910 isolated in pure culture Miller & Olson 1969 isolated virus

Clinical Signs of Disease Chronic bacterial disease characterizedLymph node enlargement, weight loss, by recurrent diarrhea, progressive digestive disturbances, exophthalmos, emaciation, plus thickening and posterior paresis or paralysis due to solid corrugation of the intestinal mucosa. tumor. Leukemia present in small percent- age of animals.

Mean Age When Clinical Disease Appears 2 to 5 years 6 to 7 years

Primary Source of Agent Contaminated feces Infected blood

Primary Site Where Agent Survives (In Vivo) Macrophage B lymphocyte (Proviral form)

(Infectious Bacteria)

Method of Transmission Infectious organism BLV Pro-Viral Infected Lymphocyte

A. Fecal-oral A. Blood

B. Milk B. Milk

C. Placenta C. Placenta

D. Semen D. NOT semen

Approx. age at time of Initial Infection birth to 6 months - Any age, but highest infection at

greatest susceptibility 1.5 to 2.0 yr.

Duration of Infection Life Long Life Long

Survivability in Environment Very long (months to years) Very Short (minutes to hrs.)

Resistance to Disinfectants Very resistant (Phenolic is best) Very sensitive (water will destroy)

Survival in meat and milk Very resistant Short survival, Sensitive to

(pasteurization does not kill) pasteurization (DNA?)

Role of Genetics in susceptibility Assumed - Complex Established - Complex

A. Infection Yes? Not Proven Yes, BOLA type

B. Disease Yes? Not Proven Yes? Not Proven

Prevalence in US

Animal

Dairy Cattle 10% 25%

Beef Cattle 5% 5%

Herd 35% (Dairy) 90% to 95% (Dairy)

Percentage of Infected Animals that

Develop Disease (by 7 yr.) >50% 0.1 to 0.3%

Species Naturally Infected All ruminants, pseudo- ruminants,

nonhuman primates Cattle

Reliability/Ease of Use of Assays

A. Serological Fair - ELISA, CF, AGID Excellent - AGID, ELISA

B. Organism Good - Culture, Probe Fair - Infectivity

Economics of

A. Infections Significant - Progressive Impact Minimal - Only if you export

on production or sell bulls to AI Centers

B. Disease Significant - New Cases Condemnation at slaughter

Public Health Implications of Crohn’s Disease - suggested that None - Perception of

Contaminated Food Product M. paratuberculosis may play Leukemia virus in meat and some role in its development milk

Regulations with regard to: United States United States

A. Sale Ethical, free status None

B. Slaughter None Condemnation of diseased

animal

C. Semen None (ethical) None

D. Embryo Transfer None None

Management/Control Minimize risk of infection Eliminate highly infectious animals - Herd Free Status

As you can readily see from a comparison of the two diseases, there are some similarities, but as expected, there are many differences. Yet the overwhelming similarity would be the perception that both of these commonly occurring bovine pathogens pose a threat to human health. Personally I believe they pose little or no risk. However if consumers decide, as they have in the United Kingdom, that the threat from Johne’s and/or Leukosis is as "unreal" as it is from BSE, only then will certain humans need to be concerned, because the health of the people in the dairy and beef industry will be in danger.