Bovine Viral Diarrhea Virus (BVDV)
Congenital defects with BVDV
- *CNS* = cerebellar hypoplasia, hydrocephalus, microencephaly, hydrancephaly, porencephaly, hypomyelination - *ocular system* = cataracts, microophthalmia, retinal degeneration, optic neuritis - *other defects* = thymic hypoplasia, alopesia, growth retardation, brachygnathism, deranged osteogenesis - type of defect you see depends on what organ system was in development at the time of infection
Characteristics of Persistent infection
- *PRIMARY reservoir and source of BVDV* - no antibodies present -- so do NOT mount immune response - higher levels of virus - continuous shedding from ALL secretions and excretions -- doesn't take a lot of blood, semen, etc. to transport virus to another animal - very efficient virus
Consequences of transplacental BVDV
- *abortion* = see throughout gestation -- can be due to cytopathic or non-cytopathic strains - *persistent infection* = pregnant cow becomes infected BEFORE 125 days of gestation with a NON-cytopathic strain - *congenital defects* = due to cerebellar disease, cataracts -- from 100 days close to before birth - *acute infection* = occurs when pregnant cow becomes infected AFTER 130 days of gestation
Prevention of BVDV
- *biosecurity* = limit movement, quarantine new animals for 30 days, test new arrivals - *vaccination* = protects against BVDV (but not 100% effective) - *surveillance* = watch if have risky behavior
Antigen capture ELISA (ACE)
- *detects viral ANTIGEN* -- conserved antigenic domain - use serum or ear notch for test - NON-formalin fixed -- use phosphate buffer saline - *accurate in PI animals!! -- NOT acute* - rapid results - inexpensive - look for color change if reaction occurs between antigen and antibody -- red color indicates BVDV
Transmission of BVDV
- *inhalation or ingestion AFTER direct contact* - contaminated vectors or vehicles (needles, syringes, balling guns) - contaminated embryos from bovine serum used in medium for transfer of embryos - contaminated semen - placenta
BVDV in other species
- *pigs* = dying and stillborn piglets; can be carriers - *sheep* = outbreaks similar to border disease virus; congenital infections with GI disease - *goats* = congenital infections with GI disease - *alpaca* = stillbirths, weak neonates, PI crias -- only BVDV-1b - *white-tail deer* = MD-like lesions, BVDV isolated, PI - *mule deer* = emaciated and weak
Diagnosis of PI animals
- *virus isolation* = serum vs. whole blood - *IHC testing* = skin (formalin must be used) - *antigen capture ELISA* = MAIN test used -- can use skin (non-formalin) or serum sample
Diagnosis of ACUTE infections
- *virus isolation* = serum vs. whole blood - *serology* = paired sera, probably NOT best choice - tend to heal themselves, so do supportive care and maybe antibiotics because BVDV is potentiator for other diseases and can get secondary bacterial infections
BVDV Genome characteristics
- 5' and 3' untranslated region - variable and conserved regions - unique autoprotease - 4 structural proteins = nucleocapsid C, envelope glycoproteins (3)
Subclinical disease with ACUTE infection
- 70-90% of BVDV infections - mild fever - leukopenia - produces serum neutralizing antibodies - see decrease in milk production - don't know they are infected, so can complicate eradication efforts
IHC staining
- ACCURATE detection of PI animals - acute infection positive by IHC is RARE - differentiation based on staining patterns -- interpretation and training - inexpensive
Treatment of BVDV
- ACUTE infection = NO treatment, just supportive care - PI = NO treatment -- CULL - mucosal disease = NO treatment - can do antibiotics with acute infections because tend to have secondary bacterial infections
Biotypes of BVDV
- BIOTYPE = phenotype (what it looks like) - based on effects in cell culture 1. cytopathic (cp) 2. non-cytopathic (ncp) - cytopathic kills the cells vs. ncp does NOT kill the cell - MOST isolates are NON-cytopathic
Break the cycle
- Cow --> Calf --> BVDV --> Cow.... - important in control and eradication of BVDV
What's the best test?
- DEPENDS upon situation - acute or PI - adult or young (maternal antibodies may interfere so use different tests) - dairy or beef - ease of sample collection
Genotypes of BVDV
- GENOTYPE = genetic makeup of virus - no real correlation between 1 and 2 and if cytopathic or not -- can be either or (just because 1 doesn't mean cp or ncp) 1. type 1 = 1a and 1b -- based on genetic differences in specific genes 2. type 2 = important because tends to be associated with severe outbreaks
BVDV risk scale
- LEAST risk = embryos - semen (certified only) - open heifers - pregnant animals (unsure fetus status) - stockyard - MOST risk = cattle jockey
*How mucosal disease is created*
- PI animal with ncp strain --> MUTATES into cp strain --> mucosal disease - FATAL within 2 weeks after onset of clinical signs
Factors determining outcome of infection
- VIRUS = genotype, biotype, virulence - HOST = immune status, immune competence - transplacental = infertility, abortions, congenital defects, PI, seropositive healthy calves - acute BVDV = subclinical, severe acute, severe acute with hemorrhagic syndrome - mucosal disease = early or late onset
Virus isolation with BVDV manifestations
- acute infection = transient viremia so has it for a few days and then gone - PI = life-long infection so present always and forever - must test isolation differently for acute vs. PI animals -- most concerned with PI because constantly shed lots of virus - when use virus isolation and get positive test, don't know if acute or PI --> test 3 weeks later - if second test positive, then PI; if second test negative, then acute
Acute infection
- animal has to have COMPETENT immune system - transient viremia -- virus circulates for 1-2 days - shed low quantities of virus - mount immune response and have serum neutralizing antibodies produced in response to virus - can see subclinical disease (nothing) or severe disease depending on VIRULENCE of strain of virus - only temporary source of BVDV in herd or environment because shed low levels
Serology
- anti-BVDV antibody detection - serum neutralization (SN) = highest dilution of serum that inhibits virus - ELISA - quick turn-around - antigen-capture ELISA = BEST diagnostic method for most labs - lab variation problematic - does NOT identify PI animals usefully - sentinel animals
Antigen detection
- antigen capture ELISA (ACE) - immunohistochemical staining (IHC) - MOST popular test for detecting antigen and most popular due to being easy sample to collect and inexpensive
Potential outcomes of PI calf
- calf becomes infected in urero with ncp BVDV and gets persistent infection - PI calf can infect ENTIRE herd -- can infect dam's new fetus when bred back, can reinfect dam, can infect other pregnant cows <125 days in gestation - calf can die within a few days
NY in 1946
- causative agent of acute diarrhea in cattle - high morbidity, low mortality - signs = fever, anorexia, depression, salivation, nasal discharge, diarrhea, abortion, ulcers of mouth, muzzle and nose - virus MUTATES a lot
1962 BVDV
- change in clinical manifestations - associated with mucosal disease (MD) now -- more fatal - signs of MD = fever, erosions of GI tract, severe diarrhea
1993 BVDV
- clinical appearance changed - similar to 1946 strain - more severe presentation due to new species of BVDV (type 2)
Antibody interference
- colostral antibodies = see in calves <4 months old (3-8 months) - timing of testing animal is important due to antibody interference -- get interference with testing - see waning of colostral antibodies around 4 months of age
Diagnostic tests & antibody interference
- colostral antibodies in serum CAN interfere with *virus isolation, ACE & RT-PCR* -- but only if we use SERUM - colostral antibodies in serum do NOT interfere with *IHC or other tests that use skin biopsies or whole blood*
How does calf get Persistent infection?
- cow that is pregnant becomes infected BEFORE 125 days of gestation - infected with NON-cytopathic strain of virus - 125 days is when fetus develops immune system and immune competence, so important that infection occurs BEFORE - before 125 days, fetus recognized virus as self and does NOT mount immune response to virus - after 125 days, fetus has competent immune system and mounts immune response -- produces antibodies and usually ok
Spread of cytopathic strain in Mucosal disease
- cytopathic biotype - goes through lymphoid tissue and LNs and circulates via lymphatics into circulation - reaches NALT (nose), BALT (bronchus), GALT (gut), LNs, thymus and spleen - from GALT, reaches mesenteric LNs and then through lymphatics and circulation, reaches intestinal mucosa - causes *blunting of intestinal crypts* --> diarrhea
Economic significance
- direct effects = disease and death loss - potentiator for other diseases -- weakens immune system to the point that it allows other disease to occur - subtle losses = immunosuppression and subfertility (abortion)
Clinical signs of acute infection
- fever - anorexia - lethargy - leukopenia - ocular and nasal discharge - oral erosions and ulcers - respiratory disease - oral papilla blunting and hemorrhage - diarrhea - decreased milk production - epithelial erosions (interdigital space, teats, vulva) - SUBCLINICAL
Clinical signs of Mucosal disease
- fever - anorexia - tachycardia and polypnea - decreased milk production - profuse watery diarrhea - diarrhea = mucosal sheds, fibrinous casts, blood and foul odor - erosions and ulcers - oral papilla - epithelial erosions maybe in interdigital regions and coronary bands, teats, vulva and prepuce
DDX when see lesions in mouth...
- foot and mouth disease - vesicular stomatitis - bovine papular stomatitis - BVDV - blue tongue - probably BVDV or BT, but call state vet anyways just in case
Hemorrhagic syndrome
- form of severe acute BVDV - associated with NON-cytopathic strain of BVDV - can see thrombocytopenia, petechiation, ecchymoses, epistaxis, bloody diarrhea, bleeding from trauma or injection, fever, leukopenia, death - cattle suffer from SEVERE acute BVDV - NOT all cattle with severe acute BVDV progress to hemorrhagic syndrome
Persistent infection
- in utero infection BEFORE 125 days of gestation - immune INCOMPETENT --> mounts NO immune response - *ALWAYS non-cytopathic* - most affected are poor-doers - prevalence 0.2-4% - VERY effective at spreading virus and can have big impact on industry - just because animal looks bad does NOT mean it has BVDV -- cannot pick PI animals out of herd
Mucosal disease lesions and findings
- infected with BOTH ncp (original) AND cp (mutated from ncp) strains - lesions caused by CYTOPATHIC strain -- caused by immune response to cp strain - post-mortem = ulcers and erosions throughout GI tract - erosions maybe in nares and upper respiratory tract - peyer's patches in small bowel are necrotic and hemorrhagic - bowel contents watery and fetid
Virus isolation
- isolate virus, then ID viral isolate using IMPA (immunoperoxidase monolayer assay) - use serum of buffy coat (WBCs) for isolation - virus lives in mononuclear phagocytic cells in buffy coat - GOLD STANDARD - most reliable for detection of BVDV - some cell lines more sensitive -- BT cells >> Btest >> MDBK - expensive
Concerns with serology
- maternal antibodies = can interfere with sample - vaccination
Testing scenario: milk samples and screen non-lactating animals
- milk (somatic cells) = RT-PCR, VI
Control & eradication programs
- not going to be able to eradicate because disease is too prevalent - control programs must ID and remove PI animals - PI animals are reservoir and transmitter
RT-PCR
- nucleic acid detection = amplification of viral RNA and binding to cDNA target sequences - pooled samples possible - training needed - expensive
Acute infection during gestation
- occurs when pregnant cow becomes infected AFTER 130 days of gestation - fetus has competent immune system when becomes infected = ACUTE - can be fetus with competent immune system OR adult -- just has to be past the 125 day mark of immune system development
Other signs of Mucosal disease
- ocular and nasal discharge - corneal edema - hypersalivation - decreased ruminal contractions - bloat - secondary bacterial infections seen as pneumonia, mastitis and metritis - *fatality 100%*
Pathophysiology of BVDV
- oral or nasal infection with cp or ncp strain - can become low or high virulence strain - virus goes to tonsil and lymphoid follicles, then through lymphatics into regional LNs - then through lymphatics into circulation --> goes to GALT (gut), BALT (bronchus), LN - can also go to thymus, spleen, BM, digestive tract epithelium, endocrine tissues, large parenchyma, heart, resp tract, urogenital tract, skin - LOWER virulence = the FEWER tissues that become infected - HIGHER virulence = the MORE tissues that become infected -- can see mucosal lesions with higher virulence - *virus retained in mononuclear phagocytic cells of lymphoid tissues*
Characteristics of BVD virus
- pestivirus genus - flaviviridae family - single-stranded, enveloped RNA virus - easy to kill - RNA viruses mutate rapidly - causes *GI, respiratory and reproductive disease* -- BIG 3 effects
Herd surveillance for PI animals
- predict that herd has problem with BVDV when see sick animal or several sick animals - PI animals = reservoir for BVDV - control programs = detect and eliminate PIs - monitoring or surveillance programs = prevent return of PI animals - several protocols for herd screening
Mutation of RNA viruses
- random and often - occurs basically any time the virus replicates -- depends on where mutation is at as to what happens to virus - mutation changes severity or appearance of virus - quasispecies population
Severe acute infection
- recognized in 1990s in US - HIGH morbidity AND mortality in ALL groups - caused by BVDV type 2 (genotype) - signs = fever, pneumonia, sudden death, abortions - gross lesions = severe and resembled mucosal disease
Biosecurity measures for BVDV
- segregate populations - closed herd - semen and bulls BVDV negative - quarantine and test new additions - do NOT bring in pregnant animals (becasue gestating fetus status is unknown) - traffic flow - prevent contact with other animals - prevent fomite transmission
Testing scenario: animals >3-4 months of age and test calves as age
- serum = VI, ACE, RT-PCR - skin = ACE, IHC
Testing scenario: test ALL animals in herd
- skin = IHC, ACE - whole blood = virus isolation, RT-PCR - probably not going to test entire herd with ACE - would know if every animal is positive for BVDV and PI
Mucosal disease
- sporadic condition -- <5% of herds affected (not all affected) - occurs when non-cytopathic strain of BVDV in a persistently infected animal MUTATES and becomes a cytopathic strain - animal now has BOTH cytopathic and non-cytopathic strains - new mutated cp strain has to be SUPER similar genetically to original ncp strain in order for animal to get mucosal disease - now when sheds either cp or ncp strain to other cows, they get acute infection
Immunohistochemical (IHC) staining
- use skin biopsies or ear notches - fixed in FORMALIN and embedded in paraffin - specific monoclonal antibody that is able to detect diverse isolates - NOT affected by maternal antibodies -- because antibodies live in serum (NOT In ear notch), so do not use serum if worried about antibodies - red color throughout dermis and hair follicles = BVDV antigen being detected for PI animal - red color limited to dermis = ACUTE BVDV infection
Outcomes of infections with BVDV
- vast difference in clinical presentation from subclinical to severe acute, infertility or seropositive healthy calves - a lot can occur due to infections -- depends on what type of virus occurs and the immune status of the host - virulence, biotype and genotype of virus affect outcome of infection
Isolation of virus
- virus isolation in cell culture - GOLD STANDARD for viruses and bacteria detection - if can culture and grow live virus, know there was live virus present in that animal
Quasispecies population/cloud
- virus mutates so rapid and quickly - start with initial virus, and every time it replicates, there is a mutation --> resulting mutant viruses are still similar to original - but, now there are several mutants created - CLOUD = original virus and ALL of the viruses within the host that have mutated - quasispecies causes antigenic, genetic & pathogenic variation
Requirements for diagnostic tests
1. ACCURATE -- prognosis, monitoring and control programs (because we don't want to miss something) 2. RAPID TURN-AROUND -- because we don't want to leave animals out there because can shed to more animals (feedlot, herd) 3. ECONOMICAL -- cost-effective
Manifestations of BVDV
1. acute infection 2. persistent infection (PI) 3. mucosal disease
Diagnosis of BVDV
1. isolation of virus 2. antigen detection 3. nucleic acid detection (reverse transcriptase PCR) 4. detection of antibodies (serology) -- serum neutralization
Testing scenarios for herd surveillance of PI animals
1. test ALL animals in a herd 2. animals >3-4 months of age and test calves as age 3. milk samples and screen non-lactating animals (#1) 4. test calves as born by #1
Effects of acute infection
Results in DAMAGE to epithelial surfaces of: - GI tract - integumentary system - respiratory system