Lecture 17: Avian Viruses Flashcards
What is the taxonomy of mareks dz
Herpesviridae > alpha herpes virus > mardivirus
How are the types of mareks disease named
Terminology
* MDV serotype 1 (gallid herpesvirus 2)
* MDV serotype 2 (gallid herpesvirus 3)
* Herpesvirus of turkeys (melagrid herpesvirrus 1)
What is the pathogenesis of mareks disease
- Induce lymphoma: infect CD4 T cells causing visceral and neural lymphoma
- Infectious virus only found in follicular feather epithelium
- Viral replication in lungs – affect alveolar macrophages and immune cells
o Can circulate and transport to lymphoid organs (spleen/thymus/bursa of Fabricius)
o Infect T cells in lymphoid organs - Become latent in CD4 T cells
How is Mareks disease transmitted
Transmit: respiratory
What are the clinical signs of mareks disease
- Chronic polyneuritis – sciatic nerve swelling (usually unilateral)
- Visceral lymphoma (liver/proventriculus/ventriculus/spleen/kidney/heart/lung..)
- Immunosuppression
- Transient paralysis/torticollis – neck paralysis
- Acute brain edema
- Acute rash
- Swollen feather follicles
- Tumor cell infiltration in wattle/cornea/pupil/skin tumors
- Increased disease susceptibility
What are the pathotypes of mareks disease
Pathotypes
* Mild
* Virulent
* Very virulent
* Very virulent + = severe immunosuppression
* Increasing bursal and thymic atrophy (not a big effect on the spleen)
What are the histo features of mareks dz
- Lymphoid proliferation in muscle, heart, and skin
What is the main other differential for mareks disease
- Main ddx is avian leukosis tumors (from a retroviral infection)
Differentiate mareks disease and avian leukosis virus
o Mareks dz: >6 weeks (avian leukosis >16 week)
Neuro signs, usually tumors on proventriculus/skin/muscle, neural enlargement and histo change
* Not seen in avian leukosis
Bursa of Fabricius: diffusely enlarged in mareks (nodular in avian leukosis)
T cells (B cells affected in avian leukosis)
Tumor from lymphoblast and lymphocytes (avian leukosis = only leukoblasst)
Horizontal transmit (avian leukosis = vertical and horizontal)
How does immunity progress in mareks disease
- Initial lung infection followed by early cytolytic infection then late cytolytic infection
- Replicate in feather follicular epithelium continuously even while latent in CD4 T cells
- Initially = innate response – transient (gone within 3d)
- 5-6d = adaptive immune response initiated
o Strong immune response
Differentiate mareks and avian leukosis*
- Main ddx is avian leukosis tumors (from a retroviral infection)
o Mareks dz: >6 weeks (avian leukosis >16 week)
Neuro signs, usually tumors on proventriculus/skin/muscle, neural enlargement and histo change - Not seen in avian leukosis
Bursa of Fabricius: diffusely enlarged in mareks (nodular in avian leukosis)
T cells (B cells affected in avian leukosis)
Tumor from lymphoblast and lymphocytes (avian leukosis = only leucoblast)
Horizontal transmit (avian leukosis = vertical and horizontal)
What methods are used to diagnose and confirm mareks disease
- Use Hx/PE: paralysis/skin nodules/grey eyes in chickens 6wk or older
- PM exam: lymphoma in skin/nerve/proventriculus/muscle + diffuse enlargement of bursa of Fabricius
- Histo: brain inflammation + pleomorphic lymphoid infiltration in skin/muscle/proventriculus/nerves
- Immunological: identify types of cells (CD4/CD8/IgM mainly)
- Confirm via immune/viral/molecular evaluation to demonstrate viral mRNA or genome in affected tumors
How is mareks disease controlled? What are the features of the control mechanisms
- Vaccine: administered at hatchery
o Reduce disease related loss but not infection
o MeHV-1 (HVT) – serotype 2
o Ga-HV3 (SB-1) – serotype 3
o Serotype 2 and 3 are non-pathogenic for chickens = do not need to modify/attenuate the virus in the vaccine
o GaHV-2 (CVI988/Rispens) – serotype 1 (live attenuated)
pathogenic and therefore must attenuate/modify the virus for vaccine
What is the relationship between virulence and the control mechanism for mareks disease
- introduction of more efficacious vaccines resulted in increasing virulence of the virus
o HVT > HVT+SSBI > Rispens = vaccine introduction chronologically (increasing efficacy)
o Virulent MDV > vvMDV > VV+MDV = associated increases of virulence over time
How does in ovo vaccination work for chickens
o At embryo day 18: in ovo vaccine is administered
Use 2.5cm needle – inject to the hub – inject into amniotic cavity most of the time (1% of the time it will hit the neck of the bird)
If it is deposited in non allantoic cavity then it isn’t effective
How does chicken egg production work and how does it relate to vaccination
o 21d for chicken egg to incubate
o Incubator:
setter compartment – 1-18d
hatcher compartment – 18 – 21d
transfer eggs at 18d = should vaccinate eggs then
o 3 membranes: (outer) chorioallantois > yolk sac > amniotic (inner)
What are 3 main benefits of in ovo vaccination for mareks disease
o Reduced window of susceptibility
In unvaccinated = immunity develops at 7 days
In vaccinated = immunity develops at 4 days
o Benefits:
reduced window of susceptibility
cost effective, 100% intake
What type of chickens is in ovo vaccination used?
o Only used in broilers:
not in layers
- the males are not kept so they don’t want to vaccinate all of them
What is the taxonomy of Infectious laryngotracheitis
Herpesviridae > alphaherpesvirus > itovirus
What is the species of virus causing Infectious laryngotracheitis
Types
* Group 1 dsDNA
* Species: gallid herpesvirus 1 (GaHV1)
What is the pathogenesis of Infectious laryngotracheitis
Path: Upper resp infection
* Viral antigens detected in the tracheal epithelium
* Induce syncytia (multinucleated giant cells – merging of neighbouring cells) – dissolve cell membranes
* Epithelial sloughing in respiratory – expose underlying blood vessels
What are the histo signs of Infectious laryngotracheitis
- Form syncytial cells in the trachea and conjunctive
What are the gross signs of Infectious laryngotracheitis
Gross
* Blood/mucus/ yellow caseous exudate
* Over time becomes a hollow caseous cast in trachea
What are the clinical signs of Infectious laryngotracheitis
Clinically
* Dyspnea, coughing
* Coughing up bloody mucus is characteristic
* Conjunctivitis
How is Infectious laryngotracheitis diagnosed? What other virus can also be diagnosed this way?
- Embryonated eggs between 9-12d
o Make hole in cell and put virus into chorioallantois membrane
If it is ILT – within 2 days you will see pock lesion (if in 6 days then it is avian pox) - Both avian pox and ILT can be diagnosed this way
What are the types of vaccines are available for Infectious laryngotracheitis? What should you reccomend
- Vaccine – eyedrop
o Modified live
o No inactivated
o Do not use the CEO vaccines – will increase virulence over time - Types of vaccine:
o TCO-tissue culture origin
o CEO- chicken embryo origin
o Recombinant fowlpox/HVT vaccine with ILTV genes = partial protection (administered in ovo or 1d)
What are the limitations of vaccines available for Infectious laryngotracheitis?
- Limitation
o Vaccine reaction
o Establishment of latency and increasing virulence
o Transmission of vaccine virus between birds and flocks increases virulence
o Involved in recombination leading to increased virulence
What are other (non-vaccine) control mechanisms for Infectious laryngotracheitis
- Mainly controlled by biosecurity
- Reportable disease
- Biosecurity
o Depopulation recommended when found in backyard flocks
In Alberta vaccination (not depopulation) is recommended
How is Infectious laryngotracheitis transmitted to backyard flocks
o Other small flock owners
o Companion animals/wild birds
o Darkling beetles
o Contaminated coveralls/boots/equipment
o Improper handling of dead birds/manure
What is the taxonomy of infectious bronchitis
Coronaviridae > coronavirus > gammacoronavirus
What type of virus causes infectious bronchitis
Type
* Non-segmented genome
* +ssRNA – enveloped
* Very large
How does infectious bronchitis transmit and what species are affected
Transmit: respiratory and fecal oral
Target: chickens (mainly)
What is the pathogenesis of infectious bronchitis
- Inhaled and goes to respiratory tract
- Causes viremia and can infect macrophages
- Impact GI/repro/cecal tonsils/urinary tract (kidneys)
- Causing reduced egg production/cystic oviduct/shell gland edema/male infertility/nephritis
o ovary/oviduct pathology – infect/affect isthmus and uterus of oviduct - Viral replication in the trachea and kidney
What are the clinical signs of infectious bronchitis
Clinically:
* production birds and young – dyspnea
* watery albumin
* brown eggs will be discoloured (become lighter)
* wrinkled/soft shell/shell-less eggs (due to inflammation)
o penguin stance: look like they are going to lay an egg (from false layer)
Which of the following statement about in ovo vaccination
against Marek’s disease (MD) is TRUE?
a Vaccination usually takes place seven days before hatch
b Vaccine is inoculated into the yolk sac
c In ovo vaccination is not as effective as post-hatch vaccination
d Vaccine is inoculated into the amniotic cavity
e Vaccine is inoculated onto the chorioallantoic membrane
D
Marek’s disease (MD) is different from avian leukosis since:
a The MD is caused by a retrovirus but avian leukosis is caused by a
herpesvirus
b MD is characterized by visceral tumors and avian leukosis is
characterized by lymphoid depletion
c MD but not the avian leukosis is characterized by neurological
signs
d Causative viruses of both MD and avian leukosis are transmitted
vertically
e Both MD and avian leukosis are commonly seen in 1-7 days old
chickens
C
Infectious laryngotracheitis virus (ILTV) infection:
a Leads to anemia and diarrhea in addition to respiratory signs
b Is endemic in commercial flocks in Canada and rest of north
America
c Is an acute infection and the causative virus is cleared in 7-10
days post-infection
d The causative virus belongs to the Family, Retroviridae
e Is characterized by dyspnea and blood-tinged respiratory mucus
E
What is NOT true about Infectious bronchitis virus (IBV)
infection:
a Causes egg production drops and poor egg quality
b Is endemic in commercial flocks in Canada
c Vaccines are not available for the control
d The causative virus belongs to the Family, Coronaviridae
e The clinical signs include respiratory clinical manifestations
B
False layer syndrome (FLS):
a Leads to poor egg quality
b Is considered a foreign animal disease in Canada
c Is associated with development of cystic oviduct lesions
d The causative virus belongs to the Family, Herpesviridae
e Affected birds suffer from respiratory clinical signs
C
What are the gross lesions associated with infectious bronchitis
Gross
* false layer syndrome: left oviduct becomes cystic due to virus infection within first 2 weeks of hens life (right cystic oviduct is normal)
o result in accumulation of egg yolks in abdominal cavity (because there is no oviduct but ovaries are still there) = egg yolk peritonitis
o penguin stance: look like they are going to lay an egg
* kidney lesions (nephropathogenic virus forms)
How is infectious bronchitis diagnosed
- sample: nasal/tracheal/kidney/interstitial/caecal tonsl swab
- stunting and curling of embryo (9-11d)
- ELISSA
- RRT PCT
How is infectious bronchitis controlled
- vaccination will prevent egg production loss (from reduced production and bad quality)
- live attenuated vaccines: administer via spray or by water
o but many strains and mutations with poor cross variant immunity
o short lives protection required multiple revaccination - live vaccine can cause mild infections
- there are recombination of vaccine and field strains
How does infectious bronchitis control compare between layers and broilers
- broiler: chicken-coarse spray vaccine on day of hatch and 10-18d
- layer: vaccine every 4-6wks beginning at hatchery until pre lay (14-16 weeks) – inactivated vaccine
