Presentation on theme: "ANIMAL CORONAVIRUSES: LESSONS FOR SARS Linda J. Saif Food Animal Health Research Program, Ohio Agricultural Research and Development Center, Department."— Presentation transcript:
Coronavirus Genetic Groups, Target Tissues and Diseases Genetic Group VirusHost Disease/ Infection Site Respiratory Enteric Other I HCoV-229E human X TGEV pig (x) X PRCoV pig X PEDV pig X FIPV cat X X Systemic FCoV cat X CCoV dog X II HCoV-OC43 human X ?? MHV mouse CNS, Systemic RCoV rat Eye, GU HEV pig X CNS BCoV** cattle X X III IBV chicken X X Kidney, Oviduct TCoV turkey X IV ?? SARS human X X ? Kidney?
SARS Transmission Droplets - close contacts Households Hospitals (Health cares workers) “Superspreaders” Airborne ? Fecal/oral ? Fomites ? Animal host: Civet Cat - Reports from Hong Kong suggest masked palm civet cat may be an animal host for SARS (Guan et al, Science Express, Sept 4, 2003) Susceptible animal models: Cynomolgus macaque- (Fouchier et al, Nature :240) Pigs- Canadian report negative, but 5-6 week-old pigs used and TGEV/PRCV serostatus undefined Avian species- USDA reported no transmission to SPF chickens, turkeys, ducks or quail Masked Palm Civets
There are 2 models for respiratory and enteric coronaviruses in animals ◆ TGEV infects small intestinal villous enterocytes; occasionally upper respiratory tract Induces villous atrophy leading to vomiting and diarrhea which are the main clinical signs Intestine Lung PRCV is a S gene deletion mutant of TGEV (same serotype) ◆ PRCV infects epithelial cells of the upper and lower respiratory tract and a few unidentified cells in the small intestine Moderate or subclinical respiratory disease occurs, but interstitial pneumonia is evident in most pigs
Summary of genetic analysis of S gene deletion area and ORF3/3a, 3-1/3b of TGEV and PRCV strains (Kim et al 2000) TGEV MILLER TGEV MILLER
Four Clinical Syndromes Occur with BCoV Infections Enteric Infections Target Age Groups Calf diarrhea Diarrhea, dehydration Intestinal villous atrophy Birth to 4 wks of age Winter dysentery Bloody diarrhea + upper 6 months to adult respiratory infection Intestinal villous atrophy Respiratory Infections Calf respiratory disease 2 wks to 6 months Bovine respiratory disease 6-9-month-old complex (shipping fever) feedlot cattle Cough, nasolacrimal discharge, pneumonia All BCoV isolates belong to 1 serotype (2 subtypes) and are pneumoenteric Only point mutations occur in the S gene of BCoV-E vs BCoV-R strains
Which tissues do coronaviruses infect? Coronavirus Infected Tissues Macaque a PigsCattle SARS TGEV-V TGEV-A (vaccine) PRCVPEDVBCoV-EBCoV-R ViremiaNT--+- Upper Resp.Tract Lower Resp. Tract ++/ Intestine+/- 1/ /-++ (colon) ++ (colon) ++ (colon) S-geneIntactPt mutations b (nt 214 and 655) Deletion ( nt) IntactPt mutations c (42 aa changes at 38 sites) a Fouchier, et al 2003 b Ballesteros et al, 1997 c Hasoksuz, et al 2002
How do respiratory coronavirus infections in animals compare to those in humans? Respiratory Coronaviruses PRCVBCoV-R Clinical signs: CoughCough ± Nasolacrimal discharge Nasolacrimal discharge + Fever + Fever ± Pneumonia ± Pneumonia. Cells infected: Nares, Trachea, Nasal turbinates Alveoli, Bronchi Trachea Alveolar macrophages Bronchi, Alveoli Lesions/ Pathology:Interstitial pneumonia Interstitial emphysema Bronchiolitis, alveolitis Duration of shedding: Nasal 3-10 days 5-10 days (17 days) Fecal Variable, 0-a few days 4-8 days (17 days)
What Factors Exacerbate Respiratory Coronavirus Infections or Virus Shedding? 1. Aerosols Higher virus titers, longer shedding and more severe respiratory disease (Van Cott et al, 1993) 2. Dose Higher dose = higher titer, longer shedding (Van Cott et al, 1993) Pigs given TCID 50 had more severe pneumonia and deaths than pigs exposed by contact (Jabrane et al, 1994) 3. Concurrent or sequential respiratory viral infections Porcine arterivirus (PRRSV) first, then PRCV after 5 days (Hayes et al, 2000) Longer shedding of PRCV after dual infection Fecal shedding of PRCV, mainly after dual infection Prolonged fever, respiratory disease and reduced weight gain after dual infection PRCV first, then Swine Influenza Virus 2 days later (Van Reeth and Pensaert, 1994) Enhanced respiratory disease PRRSV PRCV PRCV Control Pig Lung tissue
What Factors Exacerbate Porcine Respiratory Coronavirus Infections or Virus Shedding? 4. Pigs infected with the Arterivirus, PRRSV or with PRCV followed by bacterial LPS in 5 days developed more severe respiratory disease upon LPS exposure and enhanced fever compared to pigs inoculated with each agent alone (Laborque et al, 2002; Van Reeth et al, 2002) 5.Treatment with immunosuppressive agents: the synthetic corticosteroid, dexamethasone Enhanced the severity of TGEV infections (Shimizu and Shimizu, 1979) In 1 of 4 cows inoculated with WD-BCoV-E, treatment also induced a recurrence of fecal BCoV shedding (Tsunemitsu et al, 1999)
What Factors Exacerbate Respiratory Bovine Coronavirus Infections or Virus Shedding? 1.Calves with lower serum Ab titers (VN titer < 400) to BCoV were more likely to be infected and develop disease 2.Stress of shipping cattle to feedlots 3.Co-mingling cattle from different farms 4.Other concurrent respiratory infections (viruses and bacteria)
Infectious Bronchitis Virus (IBV) Pathogenesis Primary site of infection is upper respiratory tract Trachea and Bronchi Virus detection Viremia Nasal secretions Feces and Urine Disease is most severe in baby chicks Other organs infected (sites of IBV persistence with periodic nasal shedding) Kidneys (Nephropathogenic strains) Tissue tropism of one IBV strain altered from respiratory to kidney tissues by serial passage in the cloaca (Uenaka et al 1998) Oviducts Intestine
Feline Infectious Peritonitis Virus(FIPV) Pathogenesis Primary sites of infection are the pharyngeal, respiratory or intestinal epithelial cells Two major forms: Effusive- peritoneal fluid accumulation Non effusive –fever, CNS involvement Viremia occurs due to infection of monocytes Virus is distributed throughout the body in macrophages Lesions: pyogranulomas with thrombosis After antibody development: fulminant disease with 1)Immune complexes with complement, in sera and ascites fluids 2)Antibody dependent enhancement of infection
Do coronaviruses cross the species barrier? Example: Oral inoculation of calves with enteric coronaviruses from captive wild ruminants Enteric coronavirus origin: Sambar Deer White-tailed Deer Waterbuck Calf inoculation Diarrhea: Yes Yes Yes Fecal shedding: Yes Yes Yes Seroconversion to BCV: Yes Yes Yes Conclusion:Coronaviruses from wild ruminants can experimentally infect young calves (Tsunemitsu, et al 1995) Wild ruminants Cattle transmission ?
Do coronaviruses cross the species barrier? Example: Oral inoculation of poultry with BCoV-E Turkey poults Chicks Diarrhea: Yes No Fecal shedding: Yes (12 DPI) No Seroconversion to BCoV: Yes NT Conclusion:Bovine coronavirus can experimentally infect baby turkeys (Ismail et al, 2001) Cattle Bird transmission ?
EMERGING ZOONOTIC VIRAL INFECTIONS It is estimated that 75% of emerging human pathogens are zoonotic (Murphy et al,1998 Taylor et al 2001) and that 61% of all human pathogens are zoonotic (Woolhouse et al, 2002). Zoonotic pathogens that infect both domestic and wildlife hosts and have a broad host range, appear most likely to emerge (Cleaveland et al, 2001). RNA viruses are more likely to be zoonotic than DNA viruses (Morse,1997;Woolhouse et al, 2002). Viral RNA replicases lack proofreading functions leading to high mutation rates with more rapid evolution Quasispecies exist allowing plasticity within the viral population for adaptation to new hosts Zoonotic RNA virus examples: Influenza, Nipah, Hendra, Rift Valley Fever Virus, West Nile Virus, HIV, SARS CoV(?)
FACTORS INFLUENCING VIRAL EMERGENCE Introduction of virus into a new host “Virus traffic” via ecologic changes, demographic changes, human activity/behavior (Lederberg et al,1992, Morse et al, 1997) Enhanced host susceptibility (immunosuppression, preexisting health conditions, malnutrition, poilymicrobial coinfections, etc) Establishment and dissemination within the new host population Increase in host movements (global travel, rural to urban migration), density, allow for greater spread Increasing numbers of infected individuals increase opportunity for transmissible variants to arise Human activity may disseminate vectors or reservoir
CONTROL OF EMERGING/ZOONOTIC INFECTIONS Effective global disease surveillance and coordination of efforts Multidisciplinary research efforts and teams to investigate disease outbreaks For zoonotic diseases, the combined efforts of biomedical and veterinary scientists are essential, but few mechanisms currently exist to support this type of collaboration and cooperation
CONCLUDING REMARKS Enteric coronaviruses alone can cause fatal infections in seronegative young animals; respiratory coronavirus infections are more often fatal in adults when combined with other factors (shipping fever in cattle) Factors that exacerbate respiratory coronavirus infections in animals include high exposure doses, respiratory coinfections (viruses, LPS), treatment with corticosteroids Knowledge of SARS pathogenesis (using appropriate animal models) is extremely important to design effective vaccines There are no vaccines to prevent respiratory coronavirus infections except for IBV infections in chickens Vaccination for IBV (killed or live) is complicated by the existence of multiple serotypes/subtypes Only short-term protection is needed because of the short life span of chickens
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