Parvoviridae Flashcards
What are the features of parvoviruses
- small
- non-enveloped
- SSDNA
- Icosahedral symmetry
- resistant to heat, disinfectants, pH
OnLY replicate in nucleus of dividing cells
Pathogenesis of parvovirus
- Dependent on critical requirement to replicate in dividing cells
- requires host DNA machinery to replicate
- Enter through oral or nasal route
- Newborns prone —> high cell division
- Older animals have narrower tissue range
- Continuous replication
- Bone marrow and intestinal crypt (epithelial cells) continuously replicate at all ages, highly susceptible causing enteritis and leukopenia
Enteritis (small intestine inflammation) and leukopenia (low leukocyte count)
What is the immunological response to parvovirus
- Rapid response - neutralizing antibodies detected 3-5 days post infection
- cats and dogs have antibodies protecting against reinfection
- maternal antibodies transferred via colostrum, protects newborns for 5-20 weeks
- must vaccinate, begin at 6 weeks and continue monthly to 20 weeks
- There is a modified live or killed canine parvovirus - highly effective when administered in absence of maternal antibodies
- annual booster recommended
How to diagnose parvovirus
- Immunodiagnostics to detect virus in blood, faeces or tissue samples
- Haemagglutination assays
- PCR
- ELISA
- Rapid immunomigration assay
Blood antibodies is NOT recommended, prescence of maternal antibodies or ones from previous vaccines will create a false positive
How to control and prevent parvovirus
It is environmentally stable and excreted by infected host —> focus on maximizing host immunity - quarantine -Biosecurity Vaccination Disinfectant
Aldehyde or chlorine based disinfectants or BLEACH most effective
What does PPV cause?
Stillbirth
Mummification
Embryonic Death
Infertility
Explain the epidemiology of PPV
Many piggeries have disease endemic and sows can be immune
- Can remain zero positive fro 4 years and transfer passive protection to piglets via colostrum
- This can interfere with developing active immunity and some gilts may be seronegative and become infected during mating
- Shed in secretions, but remains contaminating environment eg pens due to viral stability
What is the pathogenesis of PPV
- Oronasal route or through semen
- Viremia
Reproductive disease occurs when seronegative sows are exposed to virus during gestation - Transplacental infection in sows 10-14 days post infection
- Damage to fetus occurs 40-60 days (before immunologically competent)
Infection before 70 days -> mummification
infection after 70 days -> born seropositive and healthy
INfectefd pigs can develop viremia without developing clinical disease or obvious lesions
They can develop strong humoral response and see resistant to reinfection
How to diagnose PPV
- Clinical signs and history from farm
- Viral isolation
- Histopathology of fetuses
- Haemagglutination test
PCR
Antibody tests NOT useful as no relationship to current disease status - but useful in seeing if herd exposed
How to control and prevent PPV in endemic herds
- no treatment
- ensure breeding sows and gilts are seropositive to protect virus - asntibodies in circulation means they are preventing viremia and preventing foetal exposure
- Vaccination to enhance immunity of endemic herds - esp breeding pigs being introduced
- Inactive vaccine available - homologous strain type for efficacy
- seronegative sows must be vaccinated 2-4 weeks before breeding
- short lived protection and require 6-12 month boosters
- vaccination prevents intrauterine infection and viremia
How to prevent and control PPV in non-endemic herds
Enhanced biosecurity
Quantrine ansd screening of all incoming stock - semen screening
Control of vomited movement, disinfection
- antibody or antigen screening
Treatment and separation of infected waste
All in and all out method (closed herds) - reduced contact between groups and allows more extensive disinfection
