Chapter 22 Animal Disease and the Health of Humans

1. Chapter 22Animal Disease and the Health of Humans

2. Importance of Animal Health • Production of wholesome animal products for human consumption • Zoonotic concerns (public health) • Aesthetics and pleasure • Sports (e.g. horse racing) • Economics (loss of production, cost of prevention and treatment)

3. Definitions • Health: state of complete physical, mental, and social well-being (WHO Definition) • Health: state in which all parts of the body are functioning normally • Disease: disturbance in function or structure of any organ or body part • Public Health: health of human populations (e.g. on a community basis)

4. Losses Due to Disease in USA • 10% of pigs die before weaning • 10-15% of calves and lambs die • 10% of chickens and turkeys die • Morbidity losses may exceed mortality loss • Estimated losses due to disease exceed $6.9 billion annually in the United States (>10% of total income of livestock industry)

5. Food-Related Illnesses • > 200 diseases transmitted via foods • United States has 6-81 million cases of food-borne disease and 9000 deaths/yr • ~ 90% are bacterial • Campylobacter -Listeria monocytogenes • Salmonella -Yersinia enterocolitica • Escherichia coli O157:H7

6. Methods Used to Reduce Food-Borne Illnesses • Reduce infections in animals • Modify processing procedures • Improve storage refrigeration • Educate food preparers • Carcass decontamination • Food irradiation

7. Types of Disease • Infectious Diseases • Produced by pathogens (germs) • Non-Infectious Diseases • Mechanical injuries • Digestive disturbances • Poisoning or intoxifications • Nutritional deficiencies • Abnormal cell growth (e.g. cancer) • Genetic Disorders • Metabolic Disorders

8. Disease Spread • Contact with infected animals • Polluted water • Contaminated vehicles, chutes, crates, etc. • Carrier animals • Carrion feeders • Insects and ticks • Airborne particles

9. Pathogen Entry • Respiratory tract • Digestive tract • Wound contamination • Mucous membranes of eye • Genital tract • Teat canal • Naval cord • Contaminated instruments • Insect bites

10. Body Defenses Against Disease • Body coverings (hair, skin, mucous) • Body secretions (lysozyme, other enzymes, gastric acid) • Phagocytic system (leukocytes, liver, lymph nodes) • Immune system (antibodies, “killer T cells”) • Inflammation

11. Inflammation • Reaction to injury with goal of destroying injurious agent • Five cardinal signs: • Redness (rubor), increased blood supply • Heat (calor) • Swelling (edema, “tumor”) • Pain, tenderness (dolor) • Loss of function (functico laesa)

12. Immunity • Ability to resist and/or overcome infection • May be natural (inherent, innate) or acquired (following infection or immunization) • May be active or passive • See Table 22.1

13. Definitions • Antigen = substance (usually proteins foreign to the animal) that stimulates the formation of specific antibodies • Antibodies = specific proteins (serum globulins) that react against a specific antigen (may destroy, neutralize, render insoluble, or promote phagocytosis of the antigen)

14. Natural (Inherent) Resistance • Mechanical • Skin, hair • Mucous • Physiological • Body temperature • Acidity of body secretions • Species differences (only people get measles)

15. Acquired Resistance • Passive • Antibodies produced by another animal and transferred via injection of antiserum or ingestion of colostrum • Active • Antibodies produced following infection or artificial exposure via immunization (vaccines) • See Table 22.1

16. Types of Vaccines • Toxoid (contains a toxin from the bacteria) • Bacterin (suspension of killed bacteria) • Modified live (organisms have been treated to reduce virulence, attenuated) • Polyvalent (contain more than one subtype)

17. Vaccines to Control Cancer • Marek’s Disease is a form of cancer in chickens • Can be prevented through use of fowlpox vaccine • Basis was Jenner’s observation that milkmaids exposed to cowpox virus were protected from developing smallpox

18. New Vaccine Technologies • Monoclonal production (e.g. using hybridoma cells) • Oral rabies vaccine for wildlife • Genetically engineered (use of selected antigens rather than whole organisms)

19. Genetic Resistance to Disease • Ability to prevent entrance of the infectious agent • Ability to effectively destroy the infectious agent • Differing susceptibility to nutritional diseases (differences in absorption or metabolism of nutrients)

20. Antigen-Antibody Reactions • Agglutination (clumping, interlocking) • Precipitation (precipitation of molecules from a solution) • Complement-Fixation Reaction • See Figure 22.2 • Toxin-Antitoxin Reaction

21. Testing for Disease • Physical examination • Diagnostic tests • Based on antigen-antibody reactions • Skin testing (hypersensitivity reactions) • Microscopic examinations of blood or tissues • Skin scrapings • Bacterial or fungal cultures • Fecal examinations • Chemical tests of blood or urine

22. Selected Viral Diseases Transmissible to Humans • Rabies----see Figures 22.3 and 22.4 • All mammals are susceptible • Transmitted via saliva (rarely aerosolized) • Leading species to be affected in the USA are raccoons, skunks, bats, foxes and cats • Virus causes degeneration of CNS with convulsions, drooling, madness, paralysis and death

23. Rabies (continued) • Vaccines for wildlife control • Chicken heads or fish laced with a live gentically engineered vaccine that utilizes vaccinia (pox) virus as a vector • Diagnosed via examination of brain or other tissues with a specific fluorescent-labeled antibody • Vaccines available for use in dogs and cats and at-risk people, horses and cattle

24. Newcastle Disease • In humans see conjunctivitis, fever, chills, headache, general malaise • Poultry and many wild birds are susceptible • Signs include respiratory and neurological disturbances • Killed and modified live vaccines available • The velogenic form is reportable and requires slaughter of all exposed birds (in the USA)

25. Encephalitis • Many forms---see table 22.2---primarily affect humans and horses with birds as the primary reservoir and transmission via mosquitoes • Vaccines available for use in horses • Types include: Western encephalitis, Eastern encephalitis, St. Louis encephalitis, Venzuelan encephalitis and Western Nile Virus

26. Bluetongue • Affects sheep, cattle, goats, and wild ruminants (not humans) • Transmitted by insects (Culicoides) • Symptoms are most severe in sheep • Symptoms include swollen and cyanotic tongue, oral ulcers, lameness, wool loss, pneumonia, congenital defects in offspring • No vaccine, concern regarding reservoirs in cattle have resulted in bans on exporting cattle and semen from the USA to many other countries

27. Smallpox (Variola) • In 1798 Edward Jenner noted that milkmaids exposed to cowpox survived epidemics of smallpox • Vaccines developed by growing cowpox (vaccinia) on skin of calves and using it to inoculate people • Declared eradicated by WHO in 1979

28. Foot-and-Mouth Disease • Filterable virus affects cloven hooved animals • Humans rarely affected with oral lesions • Can be carried on fomites and by birds and animals, survives 3-4 months on fomites • Devastated cattle industry of Great Britain in 2001, also losses in Netherlands and South America • 7 major viral types and over 50 subtypes make vaccination difficult • Strict requirements for importation of animals

29. Vesicular Stomatitis • Causes blisters in cattle, horses, sheep, swine and humans (plus flu-like symptoms) • Mortality is low and lesions heal • Most common in swamp areas in 10-15 yr cycles (spread by mosquitoes & gnats) • Vaccines are available for use in outbreaks

30. Contagious Ecthyma • Also called “sore mouth”or “scabby mouth” • Highly contagious in sheep and goats • Caused by a filterable pox virus • Affected people have vesicles on hands and face (contact areas) • Lesions usually resolve in 3 weeks • Vaccines are available

31. Rickettsial Infections • Intracellular parasites transmitted by infected arthropods (included their feces) • Rocky Mountain Spotted Fever • Transmitted by wood and dog ticks • 500-600 human cases annually in USA • Q Fever (Coxiella burnetii) • Ticks and tick feces transmit, rarely from consumption of milk of an infected animal • Affects sheep, cattle, people (endemic in 35 states)

32. Chlamydial Infections • Chlamydia are infectious agents with structure intermediate between viruses and bacteria • Psittacosis (Ornithosis) • Common in parakeets, pigeons, parrots, can infect poultry and wild birds • Transmitted to people by inhalation or contact with contaminated dust, feathers or urine. • Causes influenza-like symptoms

33. Bacterial Infections Causing Disease in Animals and Humans • Tuberculosis • Mycobacterium bovis infects cattle, dogs, people • Mycobacterium tuberculosis infects humans and can be transmitted to primates and dogs • Mycobacterium avium readily infects birds and pigs • These organisms can infect most homeotherms and also poikilotherms (fish and reptiles)

34. Control of Bovine Tuberculosis • Highly successful program has reduced incidence in USA from 5% in 1917 to < 0.01% today • USDA meat inspection program • Tuberculin skin testing of animals prior to movement from states lacking tuberculosis-free accreditation • Concern over presence of tuberculosis in wildlife (deer, elk, bison)

35. Federal Accreditation and Tuberculosis Surveillance • See weblink http://www.aphis.usda.gov/vs/pdf_files/tb-status_levels.pdf

36. Tuberculosis in Other Species • Swine are most susceptible to Mycobacterium avium, number of cases has decreased as swine rarely raised with poultry and swine no longer fed raw garbage • Primates are highly susceptible • Chicken are highly susceptible but rarely infected under current management practices • Feral deer in Michigan are infected

37. Brucellosis • Brucella abortus (cattle) • Brucella melitensis (goats and sheep) • Brucella suis (swine) • Organisms can infect cattle, reindeer, caribou, bison, elk, camels, yak, people, chickens, guinea pigs, hamsters, mice, monkeys, rabbits and rats

38. Brucellosis • Organisms can infect cattle, reindeer, caribou, bison, elk, camels, yak, people, chickens, guinea pigs, hamsters, mice, monkeys, rabbits and rats

39. Brucellosis in Farm Animals • Infects placenta causing abortion • Secreted into milk • While relatively species-specific cross infection can occur • Sheep and goats are susceptible to B. melitensis and sometimes B. abortus • Non-pasteurized sheep and goat milk and cheese are sources for human infections

40. Brucellosis in People • “Malta Fever” or Mediterranean Fever (goat herdsmen on Island of Malta) • Undulant fever (symptoms includes an undulating fever) • “Bang’s Disease (Bernard Bang established the organism as a cause of abortion in cattle)

41. Sources of Human Infection • Unpasteurized milk • Inhalation • Handling infected animals • Laboratory cultures • See Figure 22.6

42. Surveillance for Brucellosis • Brucellosis Card Test • An agglutination test using serum or plasma • Brucellosis Milk Ring Test • Screens dairy herds, in USA at least 4 times annually on bulk tank milk • See Figure 22.5

43. Classification of Brucellosis Status • See Figure 22.7 • USDA classifies States • Free (no infections in > 12 months) • Class A (infection rate below 0.25%) • Class B (infection rate 0.26-1.5%) • Class C (infection rate > 1.5%) • Currently NO class B or C States • Weblink: http://www.aphis.usda.gov/vs/nahps/brucellosis/

44. Prophylaxis and Control of Brucellosis • Slaughter of infected animals (no effective therapy) • Vaccination with B. abortus strain 19 or RB51 (the latter preferred as does not interfere with diagnostic tests) • Current concern centers on presence of brucellosis in wild cervids………especially free ranging bison in Yellowstone and the Grand Tetons National Parks

45. Leptospirosis • Many domestic and wild animals are susceptible • Many strains (vaccines are available) • Cattle L. hardjo and others • Swine L. pomona and others • Leptospira bacteria thrive in moist environments • Produce anemia, kidney disease, liver disease, abortions • Influenza-like symptoms in people

46. Anthrax • Bacillus anthracis is the causative bacteria • First disease traced to a microbial source and first one to have a preventative vaccine • Spores can be viable and virulent > 50 yrs • Herbivores are the most susceptible however many species including humans can be infected

47. Anthrax • Sources of infection • Ingesting contaminated feed or carcasses • Insect or other mechanical vectors • Direct contact (e.g. infected skin, hide, hair) • Inhalation (bioterriorism risk) • Prevention: cremate/bury carcasses, irradiation, vaccination • Treatment (humans): ciprofloxacin, doxycycline

48. Salmonellosis • More than 2300 serotypes • S. typhimurium causes 30% of human cases • S. enteriditis of poultry can be transmitted to people through undercooked eggs • Other sources of human infection include raw milk, undercooked meat, and mechanical spread by rodents,cockroaches and houseflies • Approximately 2 million people infected in United States annually (primarily GI signs)

49. Salmonellosis • S. dublin • Produces diarrhea and death in calves • Swine can be infected and transmit to people through undercooked meat, prevention in swine includes not feeding raw garbage to swine

50. Tularemia • Francisella tularensis • Chief vectors are ticks and flies • Dog tick, wood tick • Deerfly, horsefly • Direct contact with infected animals or inhalation of organism can also transmit • Affects mammals, birds, and reptiles • Signs in humans: fever, may last for weeks