Viral Diseases of Swine – Porcine Coronaviruses, Porcine Rotavirus and Parvovirus Flashcards
Coronaviridae
Corona - crown or halo
Single-stranded, postive-sense, RNA virus, enveloped
Fourt Genera:
-Alphacoronavirus
- Betacoronavirus
- Deltacoronavirus
- Gammacoronavirus
Porcine Coronoviruses:
Genus Alphacoronavirus
- Porcine epidemic diarrhea virus (PEDV)
-
Transmissible gastroenteritis viurs (TGEV)
- Recognized in u.s since 1946, soon after worldwide
- Widespread in U.S. herds, cases now rare
- Pathogenesis and clinical disease identical to PEDV
- no cross protection between TGEV and PEDV
- Porcine Respiratory Coronavirus
- derived from TGEV, cross-protective
- Tropism for lungs, infections usually subclinical
Porcine Coronaviruses:
Genus Deltacoronavirus
Porcine detlacoronavirus (PDCoV)
PEDV:
Epidemiology
- Was introduced into U.S. in April 2013
- identified in Europe and Asia previously
- Within 1 year: 7 million pigs died (10% of the population)
- Spread rapidly, now reported in 39 states
PEDV is seasonal,
- higher incidence during the winter,
- Pigs are the only known hosts
- Clinical presentation depends on viral isolate, age of pigs, concurrent infections, rate of group exposure
- Infectious dose of PEDV is extremely small
- exposure to a small number of virions is capable of infecting pigs
- Level of PEDV in piglet feces, 10,000 times higher than a sow feces
- Young Day old piglets
PEDV:
Monitoring
Enacted June 5, 2014: SECD (swine enteric coronavirus diseases) federal order – included PEDV and PDCoV
SECD were reportable: required to report all cases of SECD to federal animals health officials, Federal order ended March 6, 2018
PEDV:
Key Concepts
Is characterized by severe enteritis, vomiting, watery diarrhea and weight loss
Severity of PEDV infection is age-dependent
Was recently introduced inot U.S. swine spread rapidly, now widely distributed
PEDV:
Transmission
- Primary fecal/oral transmission
- some fomite transmission is possible
- contaminated feed
- environmental exposure
- +/- aerosol
PEDV:
Infection
oral exposure leads to virus replication in mature intestinal enterocytes
Neonatal pigs have long villi with more mature enterocytes permissive to replication
Neonatal pigs also have slower turnover of enterocytes
Villi:
Projections into the intestinal lumen
Involved in digestive absorption functions
Mature enterocytes
Cells survive only a few days
nonproliferative
Crypts
invagination of the intestinal epithelium around the villi
Primarily involved in secretory functions
Stem cell progenitors of hte villus enterocytes
Continually dividing
TGEV and PEDV :
Target
Villus epithelium for replication
PEDV:
Pathogenesis
- Virus replication in SI enterocytes causes cell lysis
- enterocytes and virus are sloughed and expelled in feces
- Viral shedding typically occurs for 3-4 weeks
- subclinical virus carriage in small intestine possible
Clinical disease inversely related to age
PEDV:
Clinical Disease
- All ages susceptible to infection
- Incubation short: 2-4 days
- High Morbidity
- Mortality vaires based on age
- suckling pigs:
- typically 50-80%
- Growing/Adult pigs:
- typically 1-3%
- suckling pigs:
- Clinical signs:
- vomiting, watery diarrhea, decreased appetite, weight loss, lethargy/depression, dehydration
Chronic or Endemic TGEV
- Sows immune and antibodies in colostrum/mils protects pigs while nursing
- Pigs become susceptible after weaning when lactogenic immunity wanes
- Signs usually mild:
- diarrhea, dehydration, unthriftiness
- Low mortality
PEDV / THEV:
Gross lesions
Thin, transparent intestinal walls with accumulation of large amounts of yellow fluid in the interstinal lumen
Congestion of mesenteric vessels
Edematous mesenteric lymph nodes
PEDV / TGEV:
Microscopic Lesions
Acute, diffuse, severe atrophic eneteritis
Atrophy and fusion of villi in jejunum and ileum
When to suspect PEDV in a herd
Clinical history of diarrhea in more than 50% of pigs on a site over a short period of time
PEDV:
Diagnosis
- Viral antigen and nucleic acids
- feces or intestine
- best to collect form acutely-affected live pigs
- PCR, IHC, VI, Sequencing
- feces or intestine
- Serology
- IFA, SN, ELISA
PEDV:
Treatment and Prevention
- Treatment is supportive:
- maintain hydration and provide clean, dry, draft-free environment
- Commercial Vaccines in U.S.
- Vaccinate sows/gilts pre-farrowing
- killed virus vaccine
- Generally considered incomplete protection in Naive animals
- Vaccinate sows/gilts pre-farrowing
-
Feedback:
- intentional and controlled oral exposure of sows/gilts to virulent autogenous PEDV
- Establish consistent whole herd-immunity
Immunity:
- Passive Lactogenic immunity very important
- neutralizes virus in GI tract of piglet, prevents infection
- Even though PEDV is very similar to TGEV, the viruses are genetically and immunologically distinct
- no cross-protection between TGEV and PEDV
PEDV:
Introduction Risk Factors
Exact mechanisms for introduction and rapid dissemination throught U.S. pig farms unknown
Potential contributions:
Contaminated feed ingredients
Contaminated fomites such as boots, cloting, equipment, trucks, people, and movement of infected pigs
PEDV:
Biosecurity
PEDV is sensitive to heat and disinfectants, stable inc old
cleaning/disinfection farrowing unit, trailers, trucks, equipment
Limit traffic onto farm and feedmill
Isolation of new animals – ensure introduction of negative animals
Showers/coveralls/boots for entry into faclity
PDCoV
- Intoruduced into U.S. in January 2014
- Disease presentation very similar to PEDV and TGEV
- atrophic enteritis, diarrhea, vomiting
- Diagnosis by PCR on feces/instestine
- Overall lower prevalence than PEDV
PRCV
Porcine Respiratory Coronavirus
TGEV with mutation in spike protein gene
Replicates in respiratory tract
Aerosol spread
Widespread in U.S
Usually subclinical
Immunity gives gross protection for TGEV
Significant decrease in clinical TGEV
Rotaviruses
Porcine rotavirus
Reoviridae
- Reo = Respiratory enteric orphan viruses
- Double-stranded, segmented, RNA virus, nonenveloped
- Rotaviruses are classified by group, subgroup, serotype
- 9 primary groups:
- A, B, C, D, E, F, G, H, I
- Group A historically most common
- Immunity is not cross-protective
- 9 primary groups:
Rotavirus
- Typically species specific
- Uniquitous among swine worldwide
- common disease:
- likely all swine herds infected
- All ages susceptible but significant disease usually only seen in young pigs
- Sows have varying levels of Anitbody in clostrum and milk which provide varying degrees of passive protection to nursing piglets
- common disease:
Rotovirus:
Transmission
Primary fecal/oral transmission
Exposure to carriers or virus in the environment
Rotovirus
Infection
virus infects and destroys mature enterocytes near the tips of the villi throughout the small intesting
Results in villus atrophy, malabsorption, and osmotic diarrhea
Porcine Rotavirus:
Clinical Disease
- Infections can be clinical or subclinical
- C/S:
- diarrhea usually seen during nursing or immediately after weaning between 3-6 weeks of age
- White gray to yellow pasty diarrhea, or watery diarrhea lasting 2-5 days
- Moderate dehydration, rough hair coat, poor growth, decreased appetite, +/- vomiting
- Variable morbitity
- Annual mortality rates of 7-20% of nursing piglets and 3-15% weaned
- diarrhea usually seen during nursing or immediately after weaning between 3-6 weeks of age
- C/S:
- Co-pathogens and poor husbandry increase severity
Porcine Rotavirus:
Lesions
Thin, flaccid and transparent interstinal walls
Villus atrophy and fusion, epithelial hyperplasia in crypts
Rotavirus:
Diagnosis
Virus detection
PCR, FA, IHC, VI, ELISA, sequencing
sample feces/intestines form acutely affected pigs
Shedding can occur in non-affected pigs
Rotavirus:
Control
Lactogenic Immunity
- Important for protecting
- endemic infections common:
- varying levels of maternal Antibody provided in milk/colostrum
- endemic infections common:
Rotavirus:
Control:
Good Husbandry and Supportive therapy
Cand reduce severity of outbreaks
Rotavirus:
Control:
Virus is very stable and persists in Environment for Months
- Fairly resistant to temperatur, pH, disinfectants
- Bleach effective
- Hish Standards fo sanitation
- cleaning / disinfection between farrowings
Rotavirus:
Control
Commercial Vaccines
Both modified live and killed vaccines
Limitaitons due to lack of cross-protection
Rotavirus:
Immunity
Require antibodies in the intestine
IgA important
IgA in colostrum and milk protective
Mother susceptible = piglets susceptible at birth
Mother immune = piglets susceptible 1-3 days after weaning
Difficult to stimulate acitve immunity while piglets are nursing immune dams
