Feline Resp. Case SDL Flashcards
Which of the following viruses does Nobivac Tricat Trio vaccine aim to protect cats against ?
Feline calicivirus, feline herpesvirus, feline panleucopenia virus
What type of vaccine is Nobivac Tricat ?
live attenuated
What does the term chemosis mean
swelling of conjunctiva
explain why feline herpesvirus (FHV) is a possible infectious cause of Marmalade’s presentation
Marmalade is a 6-year old male neutered DSH cat in a single-cat household with outdoor access. He has been vaccinated annually with the Nobivac(r) Tricat Trio vaccine, MSD Animal Health, starting with a kitten course at 9 and 12 weeks of age. Marmalade has spent 7 days in a local cattery. Within 2 days of returning home his owners report that he has developed runny eyes and is sneezing.They have brought him to be examined by the vet, with whom you are seeing practice.
FHV targets the eyes and the upper respiratory tract. Primary infection often presents as cat ‘flu in kittens. Following clinical recovery, FHV remains latent in the nerve ganglia of the head. Subsequent to a period of stress, the virus can be re-activated (recrudescence) and may cause clinical signs, which are often mild and localised. FHV is a lifelong infection.
The other differential diagnoses for feline conjunctivitis are Chlamydophila felis and Mycoplasma felis. However, the history of cat ‘flu and recent stress (cattery) suggests that FHV is the most likely diagnosis.
Should you wish to self mark - award marks for the following up to 5 marks maximum :
1) FHV affects eyes as well as respiratory system
2) can cause cat ‘‘flu’ on primary infection
3) infects for life (as virus remains latent in ganglia)
4) it causes recurring infections , often milder disease than primary infection
5) recrudescence of virus can be associated with stress
6) comment re differential diagnosis and/or other justification of choice of FHV
The vet decides to submit a sample to confirm a diagnosis of FHV infection. The following is a list of commercially available tests for FHV:
- FHV neutralisation assay
- FHV isolation
- FHV real-time PCR
If you do not know what these tests are then read the relevant section of the ABCD article on feline herpesvirus.
Choose the test that BEST fits the following statements:
Not suitable for vaccinated cats?
Highly sensitive; very low virus loads can be detected
Highly specific; false positive results should not occur
- Not suitable for vaccinated cats → FHV neutralisation assay
- Highly sensitive; very low virus loads can be detected → FHV real time PCR
- Highly specific; false positive results should not occur → FHV isolation
The most appropriate test in this case is the FHV real-time PCR assay, since very low virus loads are shed following FHV recrudescence. From the options below, choose the best sample to submit to this diagnostic laboratory:
*VTM = viral transport medium
Select one:
Oropharyngeal swab in Amies medium
Faeces
Dry conjunctival swab
Whole blood
Serum
Dry conjunctival swab
This is a graph showing the FHV real-time PCR results obtained by the laboratory:
- A real-time PCR machine detects the target DNA sequence using what technology?
- How many PCR cycles were run in this assay?
- How many replicates were run for each samples?
- Which sample had the highest viral load?
- What was the approximate Ct value for Marmalade’s sample?
- Fluorescence
- 40
- 3
- sample 1
- Ct 32-34
How is the Ct value calculated?
derived from the intersection of the threshold line with the amplification curve
False positive real-time PCR results can occur for FHV. Give 2 potential causes of a false-positive result in this test
- fluorescein eye drops
- lab contamination by PCR product (containing the genetic sequence targeted in qPCR assay)
- vaccine virus
According to the datasheet for this vaccine product, what is the aim of vaccinating a cat against FHV?
select one
To reduce the clinical signs caused by FHV
To prevent FHV shedding
To prevent the clinical signs caused by FHV
To reduce FHV shedding
To provide sterilising immunity to FHV
To reduce the clinical signs caused by FHV
Although not specified on the product data sheet which of the following additional outcomes might also be expected from the herpesvirus component of the vaccine
Select one:
To prevent the clinical signs caused by FHV
To reduce FHV shedding
To reduce the clinical signs caused by FHV
To prevent FHV shedding
To provide sterilising immunity to FHV
FHV vaccination does not prevent infection of cats with circulating (wild type) strains of FHV in the environment. Reducing the length of time for which (wild type) virus is shed in infected animals results in reduction of levels of virus in the environment and thus limits virus spread to other individuals within a population of animals. Thus although reduction of clinical disease is a primary aim of vaccination, reduction of (wild type) virus shedding is also often a desired outcome of vaccination.
The correct answer is: To reduce FHV shedding
Explain why false negative results are common with FHV testing, irrespective of what test is used.
FHV infections may be latent. FHV is shed intermittently and for short periods following recrudescence. Thus, although clinical symptoms may have been associated with feline herpesvirus recrudescence, by the time sampling occurs virus shedding may have ceased. qPCR for FHV requires presence of FHV genome in sample submitted to lab.
Other valid answers - degradation of virus/genome between sampling and receipt by diagnostic lab, insufficient virus/genome present for positive assay result (especially for less sensitive virus isolation test (which assays infectious virus)), failure of some step in the qPCR assay (though the lab should be able to detect this last example by use of appropriate controls and should then re-analyse the sample)
Are Marmalade’s clinical signs attributable to a vaccine failure? Discuss.
Probably not. Marmalade was likely to be infected with FHV as an 7-week old kitten (clinical history of cat ‘flu), which was prior to vaccination. Consequently infection with FHV is lifelong. In any event, the vaccine does not prevent infection with FHV, and is used to reduce the clinical signs caused by FHV.
Boarding catteries take measures to minimise outbreaks of respiratory disease. Apply the most appropriate measures to each specified aim
- Prevent spread of viruses via sneezed droplets
- Reduce the concentration of virus in the environment
- Prevent indirect spread between cats
- Ensure adequate protective titres to reduce clinical signs
- Prevent FHV recrudescence
- house cats individually with solid barriers between cats
- Provide adequate ventilation, low relative humidity and optimal environmental temperatures,
- Disinfect hands between each pen
- Only admit fully vaccinated cats
- Minimise stress
Which ONE of these antiviral drugs used to treat FHV-associated disease is licensed to treat named virus infections in UK cats?
Select one:
Recombinant feline interferon omega
Famciclovir
Acyclovir
Recombinant human interferon alpha
Recombinant feline interferon omega
