bovine viral diseases 1 - Steph Flashcards
BVDV stands for
bovine viral diarrhea virus
most common BVDV strains
BVDV1 and BVDV2
which subtypes of BVDV are most common
Type 1a and 1b and 2a and 2b
what is the most prevalent strain in cattle
Type 1b - likely because most vaccines have types 1a & 2a
what is the most important gene in BVDV for mucosal disease?
NS2 and NS3
BVDV host range
cattle, cervids, rabbits, sheep, goats, camelids, moose, goats, pigs, java mouse deer
To be a potential wildlife reservoir for BVDV, the animal species must (4 requirements)
1) be susceptible to BVDV
2) shed BVDV
3) maintain BVDV in the population AND
4) have sufficient contact with cattle that allow spillback infections
can pigs get BVDV
yes by getting fed raw milk or presence of cows & sheep
pigs BVDV clinical signs
poor conception rates, abortion, and stillborn piglets but can also appear without clinical signs
pig prevalence BVDV
2-43% in NA herds - so we do not know
BVDV clinical signs in lambs
lambs do a lot of shaking - called hairy shakers
BVDV clinical signs
not eating, diarrhea
BVDV infection month 1 of gestation consequences
early embryonic death & return to estrus
BVDV infection month 2-4 of gestation consequences
persistently infected - antibody negative OR abortion/malformation
Why does BVDV cause persistent infection if dam infected at 2-4 months gestation?
At around 4 months/120 days, the fetus decides what is self/non-self. Because the infection takes place BEFORE this distinction, the virus is considered part of self. ONLY virus that does this
how does BVDV target different organs for malformation?
BVDV targets cells multiplying quickly - whichever organ is growing quickly at the time of infection is the one that gets malformed
BVDV infection month 5-9 of gestation consequences
normal animal - antibody positive OR cause abortion/malformation
where can you find BVDV (pathogenesis)
Oronasal infection, tonsils - lymphatic spread, regional lymph nodes - blood circulation - lymphoid tissue of GI and lungs, thymus/bone marrow/spleen, and all other organs depending on virulence of virus
in persistent infections (PI) where do you find BVDV
ALL organs are BVDV positive - only bile + feces didn’t have any but they’re hard to find anything on PCR
does having BVDV suck for the animal
yes its extremely immunosuppressive
two biotypes of BVDV
cytopathic and noncytopathic
what causes cytopathic BVDV
a mutation in NS2/NS3 gene which causes disease to deteriorate every mucosal surface of body
can you transmit the mutation of BVDV
No, same as FIP
mucosal disease
other name for cytopathic BVDV (mutation has occurred)
how to treat mucosal disease
euthanize
why does mucosal disease exist?
we don’t know - probably there’s an evolutionary reason but we haven’t found it yet
is it hard to get rid of BVDV
very hard
Alberta seroprevalence of BVDV 1 & BVDV 2
28.4 % and 8.9%
Alberta herd level seroprevalence of BVDV 1 & BVDV 2
53.4% & 19.7%
is BVDV control voluntary in NA
yes, and various European countries and regions have demonstrated that measures on a voluntary basis are inadequate to achieving freedom from disease
where is an easy place to get diagnostic sample for BVDV
ear notch
is finding PI animals then killing them a successful control strategy
yes, very effective! Ear notch ASAP & if PI, euthanize
when finding PIs, where should you start?
-serological evaluation of oldest non-vaccinated animals (6 months + as passive immunity is fading but not vaccinated yet)
- Bulk tank PCR (then individual ELISA)
Individual animal assessment after bulk tank
Ear notch, blood, or milk ELISA
is ear notch or serum a better sample for detecting BVDV?
ear notches because in serum, antibodies are already attached to virus so harder to find
if you have many cows and one is way smaller, which one is likely to be the PI?
the way smaller one
Has vaccination changed BVD prevalence over time?
no, because the vaccines do not always contain the correct strain
are there many or few vaccination options for BVDV
many! Modified live & killed vaccines both available
is vaccination common fro BVDV
yes, >90% of cow calf producers in Western Canada vaccinate their cows and >95% of their replacement heifers against BVDV (survey of 93 herds)
are dairy or beef herds more likely to have PIs
dairy because there are always pregnant animals around
why is it so devastating on unvaccinated beef herds when virus gets introduced?
synchronized breeding (all fetuses approximately the same age)
almost all or all calves become PI (if BVDV comes in at the 2-4 month mark)
What does vaccinating the PIs out of the herd mean?
vaccine induced mucosal disease - inject animal with cytopathic BVDV and animal won’t be able to respond to it as immunosuppressed - this causes mucosal disease & the animals eventually die
does vaccinating the PIs out of the herd work?
no! First, VERY inhumane :( and only about 25% of PIs will succumb to mucosal disease after vaccination
most effective BVDV strategy
1) find PI and euthanize
2) Make sure no new PIs for 1 year
3) close farm ideally
vaccinate between 6 months & 1 year
What does BLV stand for
Bovine Leukosis Virus
Why is BLV important in dairy
-Causes about 3% less milk per infected cow
-Infected cows are 23% more likely to get culled than non-infected
-Clinical Leukosis causes losses
-Export restrictions
-Animal Welfare
-Consumer concerns
why is clinical leukosis bad
-Death of infected animals
- Condemnation of carcasses
the greater the number of BLV positive animals, the __________ average milk production
lower
are BLV+ cows more likely to be culled
Yes - but we don’t know why.
why are BLV+ animals more likely to be culled
we dont really know but maybe B cells are infected which decreases immunity so maybe that causes more lameness, mastitis, metritis, and they give less milk, fat, and protein
has BLV been increasing in prevalence in USA?
yes - 1975 was 10% and in 2017 was 43%
CanWest DHI sample - prevalence AB (herd-level and individual)
84% herd-level nd average 40% of animals within a herd were infected
where does BLV infect
B lymphocytes (CD5+)
BLV makes a copy of its genome and inserts it
in the DNA of the cow (Provirus)
BLV Infection leads to 3 different versions of clinical signs
- asymptomatic/aluekemic stage
- Persistent lymphocytosis
- Leukemia/Lymphoma
BLV Asymptomatic/Aleukemic stage
don’t have increased amount of WBC in blood
BLV Persistent lymphocytosis prevalence and clinical signs
30% of animals infected - always have increased WBC in blood
BLV Leukemia/Lymphoma prevalence and clinical signs
0.1-10% of the Persistent lymphocytosis animals
develop tumours
when BLV happens, what happens to B and T cells
polyclonal expansion of B cells which somehow causes abnormal function of T cells and monocytes (cytokine production and surface receptor expression alterations)
B cell # increase & at same time T cell # decrease
how does cancer of the white blood cells develop?
-clones of B cells may become pathogenic and become tumours
- provirus induces genes upstream and downstream which can induce oncogenes
- can also induce genes in trans which produces tumours somehow
what is a provirus
the genetic material of a virus as incorporated into, and able to replicate with, the genome of a host cell.
what does retrobulbar process leading to exophthalmus mean
tumour tissue grows and pushes eyes out of their socket - if you see this, check for BLV
can BLV lead to generalized edema
yes, means circulation isn’t going well
can BLV lead to enlarged lymphnodes
yes
can BLV lead to cardiac lymphosarcoma
yes - tumour tissue around heart & can also cause lymphosarcoma of spleen and intestines
how is BLV transmitted between animals
blood, colostrum, milk, in the uterus, and natural breeding (not through semen but through wounds during mounting)
when should you do an ELISA for BLV
36 days post infection - retrovirus so won’t detect it earlier
when should you do a PCR for BLV
26 days post infection
does BLV have variation in proviral load in blood?
yes - wide variation in peak proviral load. Proviral load is established early following infection
BLV - how does number of viral copies in blood affect infected animals?
increased number of viral copies in blood - more likely to be leukemic animals
is testing for BLV infection difficult?
no, a relatively simple antibody test that is very reliable, quick, not expensive
what can you test for BLV infection
blood and milk
should you test for BLV
yes, essential for a targeted control program + monitoring progress. Also part of proaction
how do you get rid of BLV?
prevent new infections!!! Find management practices that involve blood, colostrum & cause transmission & change them then MONITOR !!!
Examples of management practices that spread BLV
-colostrum
- ear notcher
-reusing the same needles
-flies
-using same rectal sleeve
-using the same hoof trimmer
- natural breeding
BLV - which animals should you test?
introduced animals, any animals that leave farm (cattle shows, etc)
most important causes of BLV infection
blood & colostrum spread
is management prevention of BLV hard?
YES! many variables
BLV- why is the proviral load of animals important?
gives a good idea of which animals to cull asap (High proviral load) vs can keep longer (low proviral load)
BLV - the more proviruses an animal has, it has a(n) ______________ chance of transmitting the disease and a(n) ____________ probability of getting tumours
increased, increased
do proviruses make products
yes
what do provirus products do
we don’t know
what is the threshold for considering culling an animal?
50% proviral load
if an animal has increased lymphocytes, what also increases
proviral load
is there a vaccine for BLV
no, but management practices can reduce virus burden in herd
is there a vaccine for BVDV
yes - and works very well but will not eradicate the virus from popn
has BVDV or BLV been eradicated in many western countries?
BVDV
