Lab 3.5 Flashcards
Went to see a flock with increasing deaths per day. Neurological signs are evident.
Five diseased birds were sent for further examination and testing in the local diagnostic laboratory:
* Enlarged, yellowish sciatic nerves in 2 birds
* White nodules were seen in the spleen and liver of four chickens
What is your differential diagnosis?
- Marek`s disease (Gallid herpesvirus 2)
- Lymphoid leukosis
- Newcastle disease virus
- Avian encephalomyelitis
what tests should we do if we suspect Marek’s disease? What is our target virus, and what samples should we use?
- PCR to support clinical findings + postmortem + histology
- Target: Gallid herpesvirus 2 nucleic acid (DNA virus)
- Samples: 1 mL blood (live animals); tissues, feather tip (postmortem)
forms of Marek’s disease and what they look like:
Classical form; neuro signs
Ocular form
Acute form; liver, spleen, gonads, heart, lung, kidney, muscle, proventriculus lesions
Follicular/cutaneuous form
Marek’s disease pathogenesis:
Gallid herpesvirus 2
>respiratory tract
>lymphoid tissue
>viremia
>feathers
>virus shedding
AND/OR
>lymphoid tissue
>immunosuppression, transformation
>neoplasia; skin, parenchymal organs, nerves
How is Marek’s disease transmitted?
MDV invades lung air apce and infects epithelial cells
>MDV infects cells and spreads to the feather follicles to replicate
>birds shed MDV particles in skin dander
> Birds inhlae MDV particles from dust in the environment
How do we vaccinate for Marek’s disease?
-In OVO! We can vaccinate 18-day-old embryos!
-The chick has the best possible start when it hatches and
better disease resistance from day one
-Manual subcutaneous vaccination is susceptible to human errors, while in ovo vaccination systems deliver the right dose in the right location
-Minimal chick handling, which reduces bird stress
Why do animals get diseases if they have been vaccinated against?
- Particularly virulent strain of virus
- Vaccine failure?
> Wrong administration route
> Not administered in correct quantity
> Poor preservation (e.g. vaccine got too hot/cold/old) - Non-responder to the vaccine / immune status?
- Maternal antibody interference?
- Vaccine does not prevent infection, but prevents disease!
dairy farm with a closed herd aside from a single cow purchased 1 year ago
-3 sporadic abortions earlier this year
-several days ago, farmer euthanized a 2 day old bull calf due to poor balance and coordination
> other claves have no specific clinical signs but a bit unthrifty and small
you return one month later:
-calves have severe watery diarrhea with blood that has been occurring for several days
-several calves about 4-8 months old seem somewhat undersized for their age
-calves have a few ulcers on the dental pad and hard palate, and distal limbs
> calves end up dead… severe ulceration of the hard and soft palate, severe oral ulcers
* Punctate ulcers in esophagus and abomasum
* Hemorrhagic colitis
* Fibrinohemorrhagic ileitis
- Cutaneous ulceration in the distal limbs
Histopathology of ileum demonstrates severe lymphocytolysis and lymphoid depletion
What do you think?
Bovine Viral Diarrhea Virus (BVDV)
What viruses cause erosive/ulcerative mouth lesions?
- Bovine viral diarrhea virus (Flavivirus)
- Foot and mouth disease (Picornavirus)
- Infectious bovine rhinotracheitis (Alphaherpesvirus)
- Malignant catarrhal fever (Gammaherpesvirus)
- Rinderpest (Paramyxovirus)
- Vesicular stomatitis (Rhabdovirus)
*Progressing severe watery bloody diarrhea in young animals
*Oral mucosal ulceration
*Poor-doing calves (scruffiness, poor coordination, small)
*Distal limb erosions
> these are signs for what?
*Clinical presentation could fit with mucosal disease OR severe, acute BVDV
lab test for BVDV, postmortem
- To detect viral antigen:
- RT-PCR (both type 1 and type 2)
- Immunohistochemistry
- Virus isolation (~20 days)
samples to send to lab for postmortem BVDV diagnosis
Ileum with Peyer’s patch, spleen, mesenteric lymph node,
esophagus
Which serological tests should you order for BVDV? what are limitations?
Virus neutralization, BUT:
- Each neutralization assay is specific for BVDV type 1 OR type 2
- Results in 1 to 3 weeks
- Animals that have been vaccinated for BVDV will show a positive result
- Persistently infected animal: low or no antibodies
how can we confirm if an animal is persistently infected with BVDV?
- PCR or ELISA for antigen detection
- ELISA may yield false positive results
what samples should we send from live animals to test for persistent infection of BVDV?
Serum, milk from a bulk tank, ear notch
