Lecture 9: Infectious Disease Flashcards
(33 cards)
What is the principles of infectious disease control?
-Disease: complex interactions, is the result of a combination of risk factors
-Biology of the individual and biology of the interaction of the individuals (herd effect) and the agent and environment (lead to increase in infection)
-Control of disease is based on management of risk factors that may change overtime
What are principles of infectious disease control?
- ELIMINATE at herd, regional or national level
- PREVENT entry into a herd or country that doesn’t have disease (foot and mouth disease spreads really easily)
- CONTROL to keep it a manageable level in a herd or country (restrictions)
What is Bovine Viral Diarrhea Virus?
-two genotypes of the BVD virus:
-Type 1 and type 2 (increased mortality)
-Type 2 was isolated in acute clinical cases from CA and USA in the mid 1990’s-Both types are capable of causing sever disease
-There is some, but incomplete immunologic cross-protection b/w genotypes
-Therefore most vaccines contain both type 1 and 2 strains
-FOr BVDV the biotype is defined by the growth characteristics of the virus in cell culture
1. Cytopathic (CV) strains kill cells in culture
2. Noncytopathic (NCV) strains do not kill cells in cutie (associated with PI animals)
-Biotype doesn’t relate to acute virulence
TRUE OR FALSE? In a persistent BVD infection, an infection of the fetus with non-cytopathic BVDV <125d of gestation can result in the production of a persistently infected (PI) calf?
TRUE
-virus not recognized as non-self
-Virus shedding is continuous for most of the animals life (good news) most don’t survive to adulthood (bad news) if they do they are a continuous source of infection for the herd
TRUE OR FLASE? PI animals are the main reservoir of BVDV n the bovine population?
-TRUE mostly < 2years (many PI will develop mucosal disease and die by then)
What is transmission for BVD?
-Spreads by direct contact with shedder
-Mainly though viral shedding in saliva, music, semen (manure)
-In urtero (leads to PI)
Shedding:
-PI (large # and content)
-Acute, virulent type 2 (shorter duration)
-Other acutely ill animals
Where is BVDV present and what systems does it attack? not *
-upper resp. tract and lymphoid tissues are the sites of virus replication (destruction of lymphoid tissue –> immune suppression)
-Viremia (reproduction of virus) starts 3d to 8-10d after infection but duration may be as short as 2-3d for some cattle
-70-90% of infections are subclinical (no overt disease, seroconversion ie successful immune response
What are risk factors for BVD disease?
- Herd has a history of inadequate immunization (no MLV used or failure to give primary series of killed vaccine
- Animals are purchased (screening tests for BVD not performed new purchases are not isolated)
What are BVD clinical presentations?
Not *
Mucosal disease
-Only in PI’s
Per-Acute BVD
-High fever
-Off feed
-Diarrhea (with blood)
-Severe platelet depression and death
-Death within 48 hours
Acute BVD
-Fever, diarrhea, pneumonia, abortion
Immune suppression and secondary pneumonia
BVD- associated reproductive problems, abortions and congenital anomalies
What is mucosal disease? not *
-PI animals only, usually < 2yrs
-Morbidity low (few animals) BUT case fatality ~100%
-Fever, oral erosions
-Diarrhea with blood sometimes
-Die in 5-7d
TRUE OR FLASE: BVD is a congenital disease that causes cerebellar hypoplasia and calfs that are blind or cataracts, small unthrifty
TRUE
How does BVDV affect reproduction and the economic cost for the producer?
Reproductive
-Best available vaccination ~80-90% effective at fetal protection
-Reproductive problems can persist despite an aggressive immunization program
-A PI dam will always produce a PI calf
Economic
-Very small percentage of all BVDV infections are clinical
-Acute disease of highly pathogenic strain may kill 25-40% of infected animals and cause sever milk depression and weight loss (Bb not eating)
-Abortions
-Smoldering reproductive problems
What is the treatment for BVDV?
not *
-No specific treatment
-Supportive care and antibiotics for secondary infections in acute BVD
-PI calves generally die of mucosal disease or should be euthanized as a source of virus to the herd
What are some control points for BVD?
-Adequate, correctly implemented vaccination program
-MLV for fetal protection
-Intros: no nose-nose or manger/waterer contact for 3 weeks
-Test for BVD-PI in quarantine
-Vaccinate purchases in quarantine
-Isolation of animals with diarrhea and respiratory disease
-Eliminating PI’s
What is salmonellosis?
-Infection <–> Shedding <–> Disease
-1. Sporadic and 2. epidemic associated with parturient disease and “stress”
-Prevention of introduction unlikely (rodent/wild life control) sheds in feces and cows consume
-Following outbreak infection becomes endemic
-Cows = weeks-months even years
-Farm=years
-Many strains of various virulence (host-adapted vs non-host adapted (other species)
-Infects any species with an intestinal tract
-Organism is prevalent and disease is opportunistic (only affects animals immunosuppressed)
-Zoonotic (like Dublin)
What are clinical signs for most salmonella species? not *
-Diarrhea (bloody, fibrin/inflammation strings commonly in fresh cows)
-Fever
-Off-fed
-Drop in milk
-Abortions
-Calf septicemia, diarrhea and death
What are clinical sings for salmonella Dublin?
-Emerging disease in ON
-Causes respiratory sings ans septicemia
-Was diagnosed in dairy herds in northern USA and in Quebec on veal farms
-Cases now seen on ON dairy farms (7% positive rapid spread in pop)
What is the transmission of salmonellosis?
-Fecal» oral/nasal/urine (septicemic)
-Infected not clinical septicaemia not clinical ie not always showing signs but shedding
-Clinical animals shed up to 10^9/g manure
-Rumen VFA’s protective
-Infectious does in healthy adults about 10^9
-Infectious dose in off-feed cows about 10^2-10^3
-Opportunist of calves and peri-partum cows
What are critical control point for salmonellosis?
-INTRA-Herd biosecurity (restrictions movement of manure/fomites) if do buy into herd
-Separate hospital and calving pens
-Rational antibiotic use
-Separation of calves and cows in outbreak
-NOT vaccination
What is Johne’s Disease?
-Caused by mycobacterium avian, subsp. paratuberculosis (MAP)
-Thick walled bacteria very resistant to environmental destruction
-Can infect cattle, deer, bison, sheep and goats
-VERY slow growing (won’t see clinical signs for 1-2year after infection)
-Mainly in ileum (distal small intestine)
What is the transmission for Johne’s disease?
Transmission = mostly fecal-oral
-Organism shed in manure
-Contaminate feed, pasture, water, calving pen (oral ingestion of bacteria by young calves)
-In advanced stages of disease organism may pass from dam to fetus in utero OR in colostrum (very rare usually fecal/oral)
-Generally thought to infect calves < 6 m old… highest risk is newborns… but evidence that older calves can be infected (increased risk newborns)
What is the epidemiology of Johne’s Disease?
-Animals exposed as adults may become infected but don’t know infective dose
-Many animals will never develop clinical disease (only 5-10% develop signs)
-Clinical disease onset from 18m to 6+year of age (until show sings)
-Age of onset of disease may depend on level of exposure as a calf
-Bacteria may survive years on pasture
What is the pathology of Johne’s Disease?
-Intestines become thickened with bacteria and inflammatory cells
-Malabsorptive diarrhea
What are clinical signs of Johne’s Disease?
-Episodes of profuse diarrhea, weight loss but good appetite, no blood or fever
-Often in fresh cows
-Diarrhea eventually becomes chronic
-Cows usually culled before death
-Subclinical infection appears to reduce milk production
