Poultry Medicine - MAREK'S DISEASE

What is MAREKS DZ PATHOTYPIC CLASSIFICATION?

Mild (mMDV) -> Virulent (vMDV) ->Very virulent (vvMDV) -> vvvMDV

MAREKS DZ TREATMENT?

No effective treatment

Dz's Important to the Immune System

VIRUSES 1.Chicken Infectious Anaemia (CIA) 2.Infectious Bursal Disease (IBD) - aka chicken aids 3.Marek's Disease (MD) - tumour prod dz 4.Leucosis - tumour prod dz 5.Reticuloendotheliosis OTHERS 6.Mycotoxins 7.Environmental stress - (heat, cold)

WHAT IS MAREK'S DISEASE Characterised by?

mononuclear (eg T,B cell) infiltration of peripheral nerves & various viscera (eg liver,spleen,kidney, lung..heart) muscle, skin, gonad, iris

Dz's with vertical transmission

1. CHICKEN INFECTIOUS ANAEMIA (CIA,CAA,CAV) vertical & horizontal - dz of chicks <1wk 2 LYMPHOID LEUKOSIS (LL) vertical & horizontal - dz inc >4mths (@ sexual maturity) 3 NEWCASTLE DISEASE (ND) 4 FOWL POX (RARE) 5 Mycoplasma gallisepticum (MG) - CHICKEN & TURKEYS 6 Mycoplasma meleagridis (MM) - TURKEYS SALMONELLOSIS 7.Salmonella pullorum = PULLORUM DISEASE 8.Other salmonella serotypes - eg S Typhimuirum = PARATYPHOID DISEASE 9Salmonella gallinarum = FOWL TYPHOID -But mostly via feaces 10 AVIAN ENCEPHALOMYELITIS (AE) - EPIDEMIC TREMOR

AVIAN LYMPHOPROLIFERATIVE DZs Tumour producing DZ

1.Herpes virus-induced (DNA) = Marek's Dz 2.Retrovirus-induced (RNA) i.Lymphoproliferative Disease of Turkeys ii.Reticuloendotheliosis Complex iii.Leukaemia Group a.Strongly Oncogenic (oncogene) -Short Latency Period b.Weakly Oncogenic (no oncogene) - Long Latency Period - Lymphoid Leukosis (.: older birds) c.Non Oncogenic (Endogenous)

WHAT FACTORS AFFECT THE PATHOGENESIS OF MAREKS DZ

1.Virus dose 2.Virus Strain 3.Genotype of host 4.Age of host 5.Sex 6.Immune status •Maternal Ab •Immune responses •Vaccinal immunity 7 Stress (= environmental - heat/cold/nutrition) Stress -> increased corticosteroids -> immunospression-> increased susceptibility

MAREKS DZ CONTROL?

CONTROL Vaccination = principle method for control. The efficacy of vaccines can be improved, however, by strict sanitation to reduce or delay exposure and by breeding for genetic resistance. 1.Vaccination Types of vaccine - see MIMS for details attenuated Serotype 1 avirulent Serotype 2 Serotype 3 (HVT) - cell free (freeze dried) + cell associated (kept in liquid N2) •Factors to consider in programme - Type of vaccine - Age at vaccination - DO or in embryo (@ 18-19 DO) of eggs in incubation) - Maternal Ab - Challenge before immunity (if vac too late birds already exposed to virus) - Effective vaccination - Getting viable virus into chicken embryo 2.Biosecurity + hygiene - AIAO, difficult to maintain MD free flocks 3.Genetic Resistance - using different breeds, breeding for resistance

What ARE MAREKS DZ CLINICAL SIGNS?

CSx DIVIDED INTO 3 TYPES 1. CLASSICAL MAREKS DZ •Non-specific signs (depression, wasting etc. - can't move.: can't eat/drink) •Mortality (eg depression then death) •Lymphomas in peripheral nerves •Locomotory difficulties - ataxia, paralysis -eg unilateral -1 leg forward/1back 2. ACUTE MD •More virulent , mortality up to 80% •Lymphoma formation in the visceral organs •Most common 3-6 months •Rapid onset •Blindness - iris involvement (pinpoint, irregular pupils - Ocular lymphomatosis) 3. TRANSIENT PARALYSIS •Rare •Acute encephalitis -> paralysis + incoordination

WHAT SPECIES DOES MAREK'S DISEASE AFFECT?

Chicken only - no reservoirs of infection ( but can be sub clinically infected->shedding->spreading)

MAREKS DZ DIAGNOSIS?

DIAGNOSIS -DIFFICULT as organism is ubiquitous 1.Signs + lesions (eg tumours/enlarged organs, enlarged peripheral nerves) = suggestive •Marek's disease occurs at any age >3 wk. •absence of bursal tumors helps distinguish dz from lymphoid leukosis 2.Virus isolation or demonstration (PCR) - used to determine if virulent or not. 3.Ab demonstration 4.Histopathology DDx - Mareks Dz, Reticulendotheliosis, lymphoid leukosis

LYMPHOID LEUKOSIS - HOW TO DIFFERENTIATE FROM MAREKS DISEASE?

DIFFERENTIAL DIAGNOSIS - MAREKS DISEASE 1.Age- MD more likely before sexual maturity (4wks vs 16wks) 2.Bursal involvement - always with LL (nodular) - rare in MD (diffuse tumour if there is one at all) 3.Histopathology - infiltration character in MD vs. compression in LL - homogeneous cells in LL vs. mixed in MD 4.Nerve involvement in MD (1 leg forward, 1 leg back) 5.PCR 6.Can control MD with vaccination

MAREKS DZ PATHOLOGY - PM Gross Lesions

GROSS LESIONS 1.Nerve Lesions (peripheral nerves + spinal roots) - eg sciatic,sciatic n plexus, vagus, brachial nerves --> NERVES ENLARGED •Loss of striations •Discoloured •Oedematous •Enlargement 2.Lymphoid Tumours •Many organs - key locations = liver & ovary - typical cauliflower-like appearance distinctive for MD --> Enlargement, sometimes nodular •indistinguishable grossly from leukotic lesions •Bursa +/- diffuse thickening (tumours rare) i.e. not nodular - HELPS differentiate from lymphoid leukosis 3. Enlarged feather follicles may be detected at processing -> condemnation

What is MAREKS DZ PATHOGENESIS?

•Carrier birds (infected by virus from feather follicles ) - Cell associated MDV (in Feather Follicle Epithelium - where well protected) •Respiratory tract (mode of entry) -> Macrophages -> Lymphoid system (acute cytolytic infection) •-> Viraemia 1.Feather follicles-shedding (primary multiplication) 2.Lymphoma formation in nerves, visceral organs liver, gonads etc (transformation of infected T cells) Lesions - a mixture of: 1.Neoplastic cells - thymus-dependent transformed T Cells 2.Inflammatory cells - B cells 3.Immune cells - B cells (ex bursa) •No egg transmission epidermal feather follicle release-> entry via resp trCT •Carriers & Hardiness due to cell association - explain prevalence of infection

What is the aetiology of MAREKS DZ?

•Herpesvirus •3 serologically related but distinct groups: 1.Serotype 1 - Oncogenic strains (mild to very virulent) = tumour forming strains 2.Serotype 2 - Non-oncogenic strains (apathogenic) 3.Serotype 3 - HVT isolates (non-path virus ex turkeys - used to make the vaccine)

MAREKS DZ PATHOLOGY - PM Histopath?

•Type A - neoplastic •Type B - inflammatory •Type C - mild type B •Peripheral nerves - Type A & B •Visceral Organs - mainly Type A •Skin Lesions - largely Type B (inflamm response due to virus entering feather follicles)

WHAT IS MAREKS DZ ECONOMIC IMPORTANCE?

•World wide •Ubiquitous •New virulent forms emerging -> increasing in virulence