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Midterm

POPM 4230 Study Guide - Midterm Guide: Victorian Football League, Cryptosporidiosis, BacteremiaPremium

17 pages57 viewsFall 2016

Department
Population Medicine
Course Code
POPM 4230
Professor
Terri O' Sullivan
Study Guide
Midterm

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HerdPatternFollowingVirus
Introduction
Acute Disease in
Susceptible Animals
Abortions and
Early
Embryonic
Death
PI Animals
Weak or
deformed
calves
Principles of Infectious Disease Control in the context of Dairy Cattle Health
Disease: Complex interactions, result of a combination of risk factors
Biology of the individual and Biology of interactions of the individuals (herd effect) and agent and environment
Health and Disease in Balance
Control of disease is based on management of risk factors that may change over time
Eliminate at Herd, Regional, or National Level
Prevent entry into a (erd or Country that doesnt have disease
Control to keep it a manageable level in a Herd or Country ~ our only plan of action in some cases
BIOSECURITY a Definition
= the protection of people, animals and ecological systems against disease and other biological threats
Australian biosecurity CRC - biosecurity is achieved through systems that aim to protect public health, animal and plant industries, and the
environment, from the entry, establishment and spread of unwanted pests and diseases
Stop movement of things that can cause disease infectious disease control ~ need to understand disease to control disease
SCENARIO
- expanding vxd dairy herd, bought in springing heifers last month
- several milking cows develop severe diarrhea w. fevers and drop in milk production 2 die, 3 recover
- 2 wks later, 2 of these and 4 other cows and heifers abort, 2 other heifers give birth to weak calves that have difficulty walking
~a lot of diseases target an age group but this is targeting them all
BVD in ONTARIO 1991-1995
- 200 + dairy farms w. outbreaks of acute BVD
- many herds were vaccinated for BVD, BUT many animals were NOT immunized for BVD
- our failure to use vx correctly over many years was detected by the BVD virus
~ all herds were supposedly vxd but found holes in vx programs
BOVINE VIRAL DIARRHEA VIRUS
2 Genotypes of the BVD Virus: Type I and Type II
- Type )) was isolated in acute clinical cases from Canada and NE USA in the Mid s
- Both types are capable of causing severe disease (~ even though genetically different)
- Some, BUT Incomplete Immunological Cross-Protection between Genotypes
- Therefore, most vaccines contain both Type I and Type II strains
BVDV
For BVDV the BIOTYPE is defined by the growth characteristics of the virus in cell culture
- Cytopathic (CV) strains kill cells in culture
- Non-Cytopathic (NCV) strains do NOT kill cells in culture (associated w. PI animals)
- Biotype does NOT relate to Acute Virulence
PERSISTENT BVD INFECTION
Infection of Fetus w. Non-Cytopathic BVDV < 125 days of gestation can result in production of a PI Calf
- virus NOT recognized as Non-Self
- virus shedding is continuous for most of animals life AND most do NOT survive adulthood (good news)
- - BUT if they do survive adulthood they are a continuous source of infection for the herd (bad)
EPIDEMIOLOGY of BVDV
- worldwide distribution in cattle
- some European countries are actively engaged in eradication programs
- PI animals are the main reservoir of BVDV in the bovine population
- estimate 0.5-2% in population
- mostly < years old many P)s develop mucosal disease and die by then
BVD TRANSMISSION
- spreads by direct contact w. shedder
- mainly through viral shedding in saliva, mucus, semen, (manure) - OR, in Utero ( PI)
- Shedding:
- PI (large numbers and constant)
- Acute, virulent Type II (shorter duration)
- Other Acutely ill animals
BVDV INFECTION
- upper respiratory tract and lymphoid tissues are the sites of virus replication
- destruction of lymphoid tissue immune suppression
- Viremia starts 3 days to 8-10 days after infection by duration may be as short 2-3 days for some cattle
- 70-90% of infections are subclinical
- no overt disease, seroconversion ie. successful immune response
~ produces whole spectrum of symptoms from really bad to not much going on
RISK FACTORS FOR BVD DISEASE
- herd has a hx of inadequate immunization
- NO MLV used or failure to give primary series of killed vx
- animals are purchased
- screening tests for BVD NOT performed
- new purchases are NOT isolated
MucosalDisease
NCV
CV
NCV & CV
PI Animal
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CLINICAL PRESENTATIONS OF BVD
Mucosal Disease only in P)s
Peracute BVD high fever, off feed, diarrhea, death w. in 48 hours
- hemorrhagic syndrome-fever, diarrhea, severe platelet depression, death
Acute BVD fever, diarrhea, pneumonia, abortion
Immune Suppression and secondary pneumonia (or other disease)
BVD associated Reproduction Problems abortions, congenital anomalies
~ whole spectrum of disease, doesnt help us figure it out
MUCOSAL DISEASE
- PI animals only, usually < 2yrs old
- Morbidity low (few animals) BUT case fatality ~ 100%
- fever
- oral erosions (~ on soft palate)
- diarrhea sometimes w. blood
- die in 5-7 days
~ a new strain not exposed to before usually ends up killing them (different than in utero strain)
BVD CONGENITAL DISEASE
- Cerebellar Hypoplasia
- Blind or Cataracts small unthrifty
- Lack of hair (~pattern baldness, patches of missing hair)
~ exposure likely happened months prior
BVDV and REPRODUCTION
- best available vx ~ 80-90% effective at fetal protection
- reproductive problems can persist despite an aggressive immunization program (difficult to rigorously quantify)
- a PI Dam will always have PI Calf
ECONOMIC COSTS of BVDV
- very small percentage of all BVDV infections are clinical
- acute disease of highly pathogenic strain may kill 25-40% of infected animals and cause severe milk depression and weight loss
- abortions
- smoldering reproductive problems
BVD TREATMENT
- no specific tx
- supportive care and antibiotics for secondary infections in acute BVD
- PI calves generally die of mucosal disease OR should be euthanized (source of virus to herd)
BVD CRITICAL CONTROL POINTS
Prevent/eliminate PIs and Prevent Acute Disease
- adequate, correctly implemented vx program
- MLV for Fetal protection
- Introductions: NO nose to nose or manger/waterer contact for 3 wks
- Test for BVD-Pi in Quarantine (~before intro to herd)
- Vaccinate purchases in Quarantine
- Isolation of animals w. diarrhea and respiratory disease
SALMONELLOSIS
- numerous serotypes
- infection shedding disease
- Sporadic and Epidemic associated w. parturient disease and stress
- prevention of introduction unlikely (- rodent/wildlife control)
- following outbreak infection becomes Endemic
- cows = wks mths (- yrs) VS - farm = years
- many strains of various virulence (host adapted VS non-host adapted)
- infects any species w. an intestinal tract
- organism is prevalent
- disease is opportunistic
- ZOONOTIC
Clinical Signs of Salmonellosis
Most Salmonella Species:
- diarrhea bloody, fibrin casts (in severe strains) and commonly in fresh cows
- fever, off-feed
- drop in milk
- abortions ~ if serious enough
- calf septicemia, diarrhea, death in calves (~rarely kills cows but will kill calves)
different …Salmonella Dublin **
- emerging disease ~ different then Salmonellas were used to due to resp signs, sudden outbreak of resp disease in calves
- Causes Respiratory signs
- diagnosed in dairy herds in northern USA and in Quebec .. and on veal farms
- sporadic cases on ONT dairy farms
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SALMONELLOSIS TRANSMISSION
- Fecal >> Oral/nasal/urine (septicemic)
- infected does not mean clinical and clinical does not mean septicemic
- Clinicals shed up to 109 /g manure
- rumen VFAs protective
- infectious dose in healthy adults = 109
- infectious dose in off-feed cows = 102 -103 ~ infectious dose drops dramatically in animals w. depressed feed in take, after calving
- opportunist of calves and peripartum cows
Salmonellosis Critical Control Points
- INTRA-herd biosecurity restrict movement of manure/fomites
- separate hospital and calving pens
- rational Abx use
- emphasize separation of calves and cows in outbreak
- NO vaccine!
JOHNEs DISEASE
Mycobacterium avium, subsp. paratuberculosis (MAP)
- thick walled bacteria very resistant to environmental destruction
- can infect cattle, deer, bison, sheep and goats
- very slow growing (~ hard to work w., have to wait ~16 wks for it to grow on special media)
- mainly in ileum (distal S.I)
~ time until clinical disease also takes a long time, takes years
TRANSMISSION of JD
= mostly fecal-oral
- organism shed in manure
- contaminate feed, pasture, water, calving pen oral ingestion of bacteria
- in advanced stages of disease organisms may pass from dam to fetus in utero OR in colostrum
- generally thought to infect calves <6 months old, highest risk is newborns BUT evidence that older calves can be infected
~ utter contaminated, calf ingests manure and grows to develop JD but wont see it until  yrs down the road
EPIDEMIOLOGY of JD
- animals exposed as adults may become infected but we dont know infective dose
- many animals will never develop Clinical disease
- Clinical disease onset from 18 months to 6+ year of age
- age of onset of disease may depend on level of exposure as a calf
- bacteria may survive years on pasture
PATHOLOGY of JD
- intestines become thickened w. bacteria and inflammatory cells
- Malabsorptive diarrhea (~ due to thickening of the gut)
~ have diarrhea but do not loose appetite not typical of other diseases
CLINICAL SIGNS of JD
- 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 (~ not huge, but do produce less)
TX and CONTROL of JD
- NO effective tx
- goal is to remove infected animals (selective slaughter) and prevent new infections
- diagnostic tests are very imperfect
- blood or milk EL)SA for Serum Abs to MAP
- Se= 15-45%, Sp= 99.2% for subclinical
- Milk ELISA is useful to estimate herd prevalence
- Fecal culture of individuals or pooled samples
- expensive and takes up to 3 mths
- better sensitivity but still ~40 to 60%
- Direct PCR on feces
~ test produce a lot of False negs (poor sensitivity) for JD
~ dont have tests that allow us to eradicate this disease
BIOSECURITY FOR JD
- dont allow claves to eat manure
- basic control measures will help prevent salmonellosis, calf scours
- risk assessment and management plan
~ use what we know and how we can min disease, evaluate management at different steps, try to get calves away from 1st manure meal
**Johnes Education and Management Assistance Program
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