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Infectious Disease

Infectious Disease. Johne’s Disease (Paratuberculosis). Causative agent: Mycobacterium paratuberculosis Extremely slow onset, chronic, progressive, incurable, fatal minimum 18 months to clinical status incubation period up to 10 years Prevalent in 20% of US herds

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Infectious Disease

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  1. Infectious Disease

  2. Johne’s Disease (Paratuberculosis) • Causative agent: Mycobacterium paratuberculosis • Extremely slow onset, chronic, progressive, incurable, fatal • minimum 18 months to clinical status • incubation period up to 10 years • Prevalent in 20% of US herds • 5-20% of ALL dairy cattle infected • 25-30% of all herds • increasing in both dairy and beef • sheep, goats and deer also susceptible

  3. International Prevalence • Denmark: • almost half of all herds test positive • Holland: • 50 –80% of herds infected? • New Zealand: • 16 – 50% of herds infected

  4. History “Johne’s disease is not at all widespread. It does occur, however, and as the years go by it will become more and more common and will places a great tax on the cattle industry” Beach and Hastings 1922

  5. Johne’s Disease (Paratuberculosis) • Following calfhood exposure there is no evidence of infection for six months to several years • Rate of progression dependent on age, genetic background, nutritional status, management, etc

  6. Johne’s symptoms • Clinical status after “high stress” period • Progressive and fatal • Non-treatable • Primarily affects intestine and associated lymph tissues • Causes proliferation of intestinal tissue • Malabsorption diarrhea • Animal loses condition • Displays diarrhea and constipation • Decreased milk, same feed intake (until late stages)

  7. Fig 35-1. Cows with Johne's disease typically lose tremendous amounts of body weight, although feed consumption may be normal (Courtesy of Mark Kirkpatrick)

  8. Johne’s Disease (Paratuberculosis) • Apparently healthy animals can spread the disease • Test at regular intervals of 3-6 months • Diagnostic testing is often inaccurate • Fecal culture is most accurate method in live animals • False negatives are still a problem • No treatment • Prevention through keeping infected animals isolated

  9. Johne’s Transmission • Fecal-oral • Organism remains viable in feces for 6-11 months • Transplacental transfer • Organism present in milk, colostrum • Severity of infection depends on level of infective dose • Age of exposure is critical • <5% of infected animals develop clinical symptoms

  10. Age Effects • Newborn calf most susceptible • susceptibility decreases with age • not clinical - no shedding until > 9 mos. • Cows least susceptible • infection unlikely after 1 year of age • shedding rate highest in mature, clinically infected cows

  11. Costs • Lost milk costs • Lost cow value and slaughter value • Lost marketing ability of herd • Longer calving intervals • Increased mastitis • Increased vet costs • $250/cow (all cows, not just infected) • Infected 100 cow herd with average infection rate loses $25,000/year

  12. Antibody Tests

  13. Fig 35-2. Enzyme-linked immunosorbent assays (ELISA's) are a useful diagnostic tool for estimating the prevalence of Johne's disease in infected herds (Courtesy of Mark Kirkpatrick)

  14. Testing • ELISA’s and other antibody tests have high incidence of “false positives” • If ELISA or antibody test is positive, fecal culture should be used to confirm status • Fecal cultures take 16 weeks, very expensive • Negative result does not necessarily indicate uninfected cow, just non-shedding cow • Positive result is fairly accurate

  15. Fig 35-3. To confirm infection with Johne's disease, tissues can be stained for the immunohistological detection of M. paratuberculosis (Courtesy of Mark Kirkpatrick)

  16. Johne’s Disease (Paratuberculosis) • Control measures for infected herd • Reduce contamination by good sanitation • Do not spread manure on pasture land • Raise young stock in uncontaminated environment, separate from mature animals

  17. Control Program • Prevent transmission • sanitary maternity barn • clean perineal area and udder • Remove calf from dam prior to nursing, wash udder well prior to milking • feed colostrum from test-negative cows • raise “shedders” separate from “susceptibles” • spread manure on crop ground, not pasture

  18. Control Program • Reduce incidence in herd • test mature animals every 6 months • remove test-positive animals immediately • cull any apparent clinicals • regardless of test results • purchase only from tested clean herds • vaccinate infected herds • not cost-effective in clean herds • does not prevent disease, only reduces severity • interferes with antibody tests

  19. Is Johnes a Food Safety Issue? Crohn’s disease is a bowel disease in humans Overall incidence 5.6 cases per 100,000 Severe and very unpleasant condition Cause unknown, maybe infectious agent like Mycoplasma Johnes organism found in Crohn’s patients No firm link established, the evidence is still inconclusive - but the issue is a source of concern to the dairy industry

  20. Bovine Virus Diarrhea (BVD) • Incubation period of 7-9 days • Characterized by • High temperature (105-107 F) • Nasal discharge • Rapid breathing • Loss of appetite • Diarrhea • Causes abortions in pregnant cows (3-6 weeks after infection) • Decrease in milk production in lactating cows

  21. Bovine Virus Diarrhea (BVD) • Prevention • Avoid contact with infected animals • Keep away from contaminated feed and water • Isolate all incoming animals for 30 days • Treatment • Electrolytes • Antibiotics combat the secondary bacterial invaders

  22. Bovine Virus Diarrhea (BVD) • If BVD is a constant problem, vaccinate animals • Intramuscular administration of modified live or inactivated vaccines • One vaccination should last a lifetime • DO NOT vaccinate pregnant cows • Causes abortions • DO NOT vaccinate calves under 6 months of age • Ineffective due to interference from maternal antibodies from colostrum • Replacement heifers should be vaccinated at 9-12 months of age

  23. BVD control • Multiple strains exist (identify!) • Fecal-oral • Sanitation crucial • Vaccines highly effective • not 100% • BVD-PI (persistently infected) are exceptional situation

  24. BVD-PI animals • 1 in every 200 calves is PI • Infected in utero between 80 and 120 days • Infection from 120-150 days • congenital defects • weak calf syndrome • Infection after 150 days • immune response • abortion, mummification

  25. BVD-PI calves • No immune response • recognizes virus as “self” permanently • Virus replication unchecked • incredibly high shedding rates • potential threat to entire operation • Difficult to identify • Ab titers ineffective method • must directly test for presence of virus

  26. Fig 35-4. Obtaining an ear notch tissue sample for immunohistochemical diagnosis of BVD infection (Courtesy of Mark Kirkpatrick)

  27. Fig 35-5. Immunohistochemical techniques help veterinarians visualize the BVD virus in ear tissue (Courtesy of Mark Kirkpatrick)

  28. Salmonella • Invasive coliform • fecal-oral transmission • penetrates gut lining • systemic infection common • Present on up to 75% of dairies • clinical expression after stress (shipping) • Highly rate of transmission • “herd epidemics” common • high shedding rate • high mortality rate

  29. Salmonella • Pathogen associated with stress and immunocompromised animals • Calves and transition cows most susceptible • maternity barn sanitation • isolation of sick or recently purchased animals • Characterized by rapid onset and severe watery diarrhea • Weak and rapidly dehydrated • Often becomes systemic infection • Pathogen transmitted in feces • High sanitation standards are critical • Infected cattle should be isolated • Animals are responsive to antibiotics

  30. Challenges • Some strains infect people • Carriers include pets and pests • Different strains present in different herds • S. typhimirium DT 104 is problem pathogen • multiple antibiotic resistance (cassette resistance) • resistant to ampicillin, florfenicol, streptomycin, sulphonamides, and tetracyclines • use of one antibiotic selects for the rest

  31. Treatment • Identify early • Isolate infected animals • Extreme sanitary measures • cows AND people • Use appropriate antibiotic treatment • test for susceptibility • Supplemental fluids crucial • Use herd-specific vaccine if necessary

  32. Drenching Fluids

  33. HBS - One Syndrome with Several Names • HBS: Hemorrhagic bowel syndrome • JHS: Jejunal hemorrage syndrome • BBS: Bloody bowel syndrome

  34. Hemorrhagic Bowel Syndrome • Sporadic in morbidity • A typical case incidence rate is 2-3%, with some farms experiencing an outbreak form • Mortality may approach 85-100% of cases due to peracute nature

  35. Clinical Signs of “HBS” • Short incubation period – hours rather than days • Severe sweats • Bruxism (teeth grinding) • Sternal recumbancy • Lethargy (extreme depression) • Enopthalmia (sunken eyes)

  36. Clinical Signs of “HBS” • Slight bloating may be evident • Pale mucous membranes • Fluid slosh in lower right abdomen • Distended gut loops per rectal palpation • SUDDEN DEATH

  37. Post-Mortem Findings • Severe segmental small intestinal inflammation • Segmental hemorrhaging and clotting forming a functional plug. • Necrosis +/- • Impaction

  38. Diagnostics • Appearance of characteristic lesions and clinical signs • Isolation of Clostridium perfringens type A from the lesion site in high numbers. Overgrowth occurs fast. • Fecal cultures not diagnostic

  39. Treatment Efforts • Prognosis is extremely poor • Surgical intervention • Some areas of segmental clots may be massaged out to resolve the case • Intestinal resection & anastamosis is usually required to remove affected tissue • Success Rate ~ 5-10%

  40. Are Clostridial species involved? • C. perfringens type A has to be present in the diet to cause disease • Readily fermentable carbohydrate is needed to support growth & sporulate • Partial slowdown or stoppage of ingesta flow allowing proliferation of C. perfringens. • Generation time = 8.8 min.

  41. Field Observations Food Poisoning: Is there a source of C. perfringens type A (human model)? • Model of Infection Lamb Enterotoxemia: Carbohydrate engorgement or presence in small intestine in high amounts. Gut Physiology? Rumen emptying rates, local hypomotility? Serum Ca levels?

  42. Herd Breaks • Fermentable Carbohydrate • NFC levels in excess of 40%? • Which high moisture feeds are being used in the ration and at what levels? • How soluble are the starches? Wet vs. Dry Fermented Fineness of Grind

  43. Vaccination? Commercial Vaccines: Vaccination with a 7-way Clostridial bacterin/toxoid has shown little effect. C. perfringens C&D toxoid may have some effects if the infection was mixed.

  44. Carbohydrate availability Acidosis? Rumen Emptying Rate? Summary Feed Contamination Poor fermentation Contamination Intestinal Motility Ca Levels, DMI or Acidosis

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