Poultry 1: Overview, Marek's Disease
Diagnosis of Marek's disease
-history, signalment (2-5mo) -classic clinical presentation (asymmetrical flaccid paralysis) -classic gross & histo pathology signs
Gross pathology of Marek's disease (4 things)
1) Enlargement +/- yellowing and loss of cross-striations of peripheral nerves (esp sciatic nerve) *this is called neural lymphomatosis 2) Visceral tumors and enlargement of organs (ovary, lung, heart, kidney, liver, skeletal muscle, intestines, iris, skin) 3) Enlargement of skin follicles (skin leukosis) 4) Discoloration of the iris (see pic)
10 general causes of disease in chickens
1) Nutritional (deficiency, toxicity, imbalance - eg rickets) 2) Metabolic (obesity, cage layer fatigue, fatty liver disease) 3) Genetic/hereditary (predispositions, susceptibilities) 4) Congenital (egg incubation - blindness) 5) Degenerative (muscle myopathy) 6) Toxicity (ionophore, arsenic, organophosphate) 7) Management (dehydration, starvation, cannibalism) 8) Neoplasia (Marek's disease, Leukosis) 9) Diseases of high production (ascites, sudden death syndrome) 10) Infectious agents (many!)
What is the hallmark histopathology lesion of Marek's disease?
1) Pleomorphic lymphocytes (mostly T cells, some B cells)
Prevention of Marek's disease: 2 main things to do
1) Vaccination: -HVT (serotype 3) -SB1 (serotype 2) -Rispens (serotype 1) **vx = combination of all serotypes; can do in ovo or SC 2) Biosecurity (AIAO, disinfection, etc)
What are the 3 serotypes of Marek's disease virus?
Serotype 1: ubiquitous in chickens, oncogenic Serotype 2: common in chickens, non-oncogenic Serotype 3: common in turkeys, non-oncogenic
Signalment of Marek's disease
Sexually immature chickens 2-7 mo (but can occur in any age >3wks)
Etiology of Marek's disease
herpesvirus induced neoplastic disease
Transmission of Marek's disease
Direct or indirect contact (airborne, fomites); infected chickens transmit indefinitely *not vertical transmission
Where does Marek's disease virus replicate?
Epithelial cells of the feather follicle
Clinical signs of Marek's disease
Incubation period 3-4 wks; then: -paralysis (ataxia, asymmetric flaccid paresis - classic sign is one leg forward & one back while lying on side) -gasping, crop dilation (d/t vagal involvement) -weight loss, anorexia, eventually starvation & dehydration -paleness *progression to neoplasms (classical form) or death within 24-72h following onset of paralytic signs (acute form)
Pathogenesis of marek's disease
Lymphotrophic herpesvirus --> lymphocytolytic infection --> immunosuppression --> changes in cytokine expression (increase IFN-γ, IL-6, IL-18)
