Marek's Disease, Infectious Bronchitis, IBDV
What are the estimated global economic losses caused by Marek's disease and what are these losses primarily due to?
$1-2 billion annually Mortality and carcass condemnation
What is the major limitation in the control of IBDV?
A universal vaccine program can't be offered due to the extreme variability in maternal immunity, management, and regional virus epidemiology
What are some common clinical signs of IBDV?
Acute systemic disease, anorexia, depression, urate diarrhea, dehydration (a really sick bird with urate diarrhea)
Why is diagnosis of Marek's challenging? What is the focus of diagnosis?
Almost all chickens are infected due to its persistence in the environment The focus should be the tumor, not infection
What are the uses and limitations of using PCR for diagnosing Marek's?
Almost all chickens are infected with Marek's, and even those vaccinated will test positive on PCR Should be used to confirm other diagnostic test results
What are the regionally important serotypes of IBV?
Ark, DE072, GA98, Mass, Conn
In Marek's disease, for tumors that develop in the lymphoid organs, what is the most common observed sign?
Atrophy of the bursa and thymus (however, tumors are typically not present in these tissues)
What are the control methods (2) for IBV?
Biosecurity Identifying serotypes in the region and determine appropriate vaccines
To what family does IBDV belong?
Birnaviridae
What are the genetic characteristics of IBDV?
Bisegmented double stranded RNA Non-enveloped (fairly resistant in the environment)
What is the period of greatest susceptibility for broilers and layer pullets infected with IBDV?
Broilers: 3-6 weeks Layers: 7-12 weeks Chicks less than 3 weeks old won't show signs, but may have subclinical disease
What is the mortality pattern for broilers infected with IBDV? For layers?
Broilers: between 3-6 weeks old (rate of 10%), peaks on day 2-3, and ends on day 5-7 Layers: between 7-12 weeks old (rate of 30-70%), mortality between day 7-14 vvIBDV causes up to 90% mortality
What is the principle target organ for IBDV infections?
Bursa of fabricius (leads to complications in secondary immune organs as well)
What are the typical findings for IBDV on necropsy?
Bursa that is acutely swollen, then atrophies Variable hemorrhage in soft tissues and juncture of proventriculous Swollen kidneys, liver, spleen, enteritis Subclinical: bursal atrophy
True or false: An immune response to infectious bronchitis will recognize both the IBV Ch strain and the IBV C2 strain.
False (they differ vastly phenotypically, despite a difference in only a couple proteins genetically)
If using a FTA card for diagnosing Marek's, what 3 samples can be used?
Feather follicle impression Swabs Direct organ application
What is the route of transmission for IBDV?
Fecal-oral (Virus is found in high concentrations in feces and litter)
What sign will you see in IBV and E. coli infections on necropsy?
Foamy air sacs
What is currently the most effective Marek's vaccine programs for Meat-type birds: Commercial layers:
Meat-type: HVT + Rispens combo Layers: HVT + Rispens + SB1 combo
What breed of chickens develop the most severe reaction to infection by IBDV? Who has a less severe reaction?
Most severe: white leghorns Less: meat-type
What are the 5 tests that can be used to diagnose IBDV?
Pathology/ histopath Bursal index (weight of bursa/ body weight) Virus isolation RT-PCR and sequencing Serology (agar gel precipitin, ELISA)
What are the common clinical signs of Marek's disease?
Peripheral nerve paralysis, leading to leg/wing/neck paralysis Often present with unilateral paralysis (one leg forward and one back)
What is the most common histological sign seen with Marek's?
Pleomorphic lymphocyte (specifically T cell) infiltration in peripheral nerves
When should an inactivated vaccine be used to protect against IBV?
Prior to the onset of egg production (in layers and breeders) This will stimulate higher levels of circulating antibodies
What are the 5 factors that contribute to economic losses due to IBV?
Reduced feed conversion Reduced weight gain Increased mortality (in young chickens) Increased condemnations Reduces egg production/ quality
What are the 2 affects of immunodeficiency caused by IBDV?
Reduced response to vaccination Increased susceptibility to other pathogens (adenoviruses, Marek's, coccidia)
What is the vaccination protocol for IBV?
Regional serotypes need to be ID'ed Attenuated live and inactivated vaccines are available Live vaccine series should be progressively increased in aggressiveness-route (water to fine particle spray) and virulence of strain
Where does the infectious bronchitis virus replicate in the animal? Where does the virus spread to?
Replicates in the respiratory tract (will find it in the nostrils and trachea) Spreads to the kidneys and genital tract (and rarely to the GI tract)
What are the two methods of vaccination for Marek's and which one is used in the USA?
SQ vaccination at one day of age In ovo vaccination- used in the USA (done at 18-19 days incubation)
What are the serotypes of IBDV?
Serotype 1: virulent strain (not common in USA) Serotype 2: non virulent (originated from turkeys)
When should birds be vaccinated against IBDV?
Should wait until the animal has a drop in maternal immunity and a buildup of antibodies in order to get an adequate response to the vaccine
What are the genetic characteristics for infectious bronchitis (4)?
Single stranded RNA Enveloped Multiple serotypes (spike proteins) Incredibly sensitive to environment
What microscopic lesions are expected for Leukosis vs. Marek's for Skin and peripheral nerve infiltration: Cell proliferation of the bursa:
Skin/ nerve: absent in leukosis, present in Marek's Bursal cell proliferation: intra-follicular in leukosis, inter-follicular in Marek's
What component of the coronavirus genome is responsible for genetic variability, viral attachment, and tissue tropism? Allows for quick adaptation to natural selection.
Spike proteins
What is the common cause of death in birds infected with Marek's?
Starvation and/or dehydration due to peripheral paralysis
What is the basis for the current vaccine limitation for Marek's?
The Rispens vaccine is the only vaccine based on serotype 1 and is the most effective The HVT vaccine is also available but will only protect against less virulent strains
How is Marek's disease transmitted? Where does the virus replicate in the animal?
The virus resides in feather follicles, and when bird grooms the virus is inhaled. Replicates in the epithelial cells of feather follicles.
What are the treatment options for IBDV?
There are none
True or false: Marek's disease virus will survive in chicken houses for months to years, inevitably challenging each new flock added to the house.
True
What are some methods of control for Marek's?
Vaccination Good flock management Cleaning, disinfection, and biosecurity (the key is reducing the amount of virus that the chicken is exposed to since its present in every house)
When T cells are transformed into cancer cells in Marek's infections, what ultimately occurs?
Widespread metastasis (tumors can develop in almost every organ)
How many serotypes of Marek's are there? Which serotype(s) are responsible for disease? Which serotype(s) are used for vaccines?
3 serotypes Serotype 1 is responsible for disease Serotype 2 and 3 are used to create vaccines
Serotype 1 of Marek's disease has how many levels of virulency?
4 mMDV, vMDV, vvMDV, vv+MDV
What are 5 factors that can result in vaccination failure for Marek's?
Challenge with highly virulent strain Challenge in vaccine interval Immunosuppressive agents Inadequate vaccine programs Poor vaccine prep and administration
What are the 3 economic implications of IBDV?
Classic strains cause up to 20% mortality (80% in highly virulent strains) Depressed growth esp. in young chickens Severe and prolonged immunodeficiency
What are the 5 tests that can be used for IBV?
Clinical signs Seroconversion Virus isolation in embryonated eggs RT-PCR Other (ciliostasis)
What are the 5 tests used to diagnose Marek's?
Clinical signs/ necropsy Histopath PCR and sequencing (difficult, as most birds will test positive due to infection) Virus isolation Histochemistry
What are 3 common differentials for Marek's?
Coligranulomatosis Avian tuberculosis Reticuloendotheliosis
To what family does infectious bronchitis virus belong?
Coronaviridae
What are the clinical signs of IBV?
Coughing, sneezing, nasal discharge, tracheal rales Will look like every other disease causing respiratory signs
The IBV genotype isn't necessarily the same thing as the serotype, so some genes may not be expressed. What test can be used to specifically determine the virus's phenotype?
Cross neutralization (but it is expensive and labor intensive)
Genetic characteristics of Marek's disease?
Double stranded DNA Enveloped Large genome
What is the most common gross lesion on necropsy for Marek's?
Enlarged nerves and tumors (usually of the vagus, brachial, and sciatic nerves) Enlargement is due to T cell infiltration of the nerves
What subunit of a spike protein refers to the head? To the neck? Which subunit is the important target in neutralizing the virus?
Head: S1 Neck: S2 Target: S1
To what family does Marek's disease virus belong? Why is this relevant?
Herpesviridae Herpes viruses are used as vectored vaccines
What samples should be taken for the following diagnostic tests for Marek's? Histopath Isolation PCR/sequencing
Histopath: skin, eye, spleen, liver, proventriculous, bursa, sciatic nerves, tumor tissue Isolation: buffy coat PCR/Sequencing: feather pulp
What signs will you see on histopath for IBV?
Huge amounts of lymphocyte infiltration, missing cilia, but NO hemorrhage
What provides a definitive diagnosis of Marek's?
Immunohistochemistry
What factor has led to a decrease in the incidence of Marek's disease around the world?
Improvement in vaccine prep and administration
Which disease is the most economically important worldwide?
Infectious bronchitis
Term for an acute, highly contagious viral infection of young chickens that causes generalized lymphoid atrophy (of B cells) with a concomidant immunodeficiency.
Infectious bursal disease virus (IBDV)
Marek's infections that metastasize to the skin will present with what clinical sign?
Inflammed feather follicles upon defeathering
What two things must be inspected on arrival for frozen Marek's vaccine ampoules?
Inspect the Dewar exterior Inspect the inverted cane (requires PPE)
What are the vaccine choices for IBDV (4)?
Intermediate strains (attenuated and highly attenuated) Highly virulent (hot) strains (egg adapted) Variant strains (cell culture adapted) Oil adjuvant killed-virus vaccines (standard and variant)- used in breeders
Good cleaning practices that delay the exposure of chicks to Marek's to allow for the development of proper vaccine protection addresses what aspect of vaccine failure?
Interval vaccination challenge
What are the two fates for T cells affected by Marek's disease?
Latent infection, go on to replicate in feather follicles and allow transmission. Become tumor cells, ultimately leading to death
What is the age of onset of Leukosis vs. Marek's?
Leukosis: 16 weeks old Marek's: 4 weeks old
What is the expected presentation (paralysis/ paresis) in Leukosis vs. Marek's?
Leukosis: absent Marek's: usually present
What is the peripheral nerve and ganglion involvement in Leukosis vs. Marek's?
Leukosis: absent Marek's: usually present
What gross lesions occur in the bursa of fabricius in Leukosis vs. Marek's?
Leukosis: nobular tumors Marek's: diffuse enlargement or atrophy
What skin and muscle tumor presentation is expected for Leukosis vs. Marek's?
Leukosis: usually absent Marek's: may be present
A highly contagious neoplastic disease of poultry characterized by T-cell lymphoma and enlarged peripheral nerves.
Marek's disease
