ANSC 605 Viral Diseases

Mareks Disease and Transmission

Herpesvirus, enveloped DNA virus

• Stains vary in virulence

Ubiquitous in commercial flocks

• Primarily in chickens but also reported in turkeys

Virus multiplies in feather follicles

• Transmission by inhalation of infected dust or dander

• Highly contagious and can survive in environment for months 

• Once virus is introduced into a flock, regardless of vaccination status, infection spreads quickly from bird to bird 

Mareks Disease Signs

Can invade and transform lymphocytes

• Cancer-like disease (oncogenic virus) 

Variable presentations:

• Death with no prior signs 

• Infiltration of nervous system by abnormal lymphocytes 

• Paralysis of legs and wings, dysfunction in GI motility 

• Can be temporary or persistent 

Mareks Lymphoid Tumors

• Accumulation of abnormal lymphocytes in organs and in feather follicles 

Incidence of disease in flock depends on:

• Strain and dose of virus 

• Age at exposure 

• ± passive transfer of maternal antibodies 

• Host genetics 

• Strain and dose of vaccine virus 

• Several environmental factors, including stress

Mareks Diagnosis and Prevention

• Carrier state possible

Diagnosis based on the presence of tumors and the presence of disease in chicks

• Differentiate form similar diseases by performing viral PCR on tumor

Prevent with good biosecurity and vaccination

• Administered day one of life or while still in its egg

Fowl Pox

Avipoxvirus

• DNA virus in Poxviridae family

• Can survive in environment for long periods

Transmitted through direct contact with lesions, aerosolized virus from shed scabs, carrier mechanically by biting insects

• Infection spread slowly through flock

Fowl Pox Wet vs Dry forms 

Diphtheritic (wet) form 

• Plaques along lining of GI and resp. tracts 

• Can cause difficulty eating and breathing 

• High mortality 

May result in decrease in weight gain and egg laying in infected birds 

Typically diagnosed based on characteristic lesions or biopsy 

• Can perform advanced viral testing (PCR, viral isolation) 

Fowl Pox Prevention and Treatment

• Isolate infected birds

• Infected birds that survive can develop protective immunity

Vaccination is possible and recommended in high-risk areas

• Can be performed as a preventative in young birds

No zoonotic risk 

Infectious Laryngotracheitis (ILT)

Herpesvirus, DNA virus, enveloped

Signs: coughing, nasal discharge, conjunctivitis, difficulty breathing, blood in trachea, anorexia

Transmission

Infectious Laryngotracheitis Diagnosis and Control

• Necrotizing tracheitis with hemorrhage and casts (dead tissue) in trachea

Diagnosis: based on signs, biopsy of trachea, PCT

Vaccination common in high-risk areas

Infectious Bronchitis

Coronavirus, enveloped, RNA virus

Signs:

• Respiratory distress

• Decreased egg production and poor egg quality

• Some strain effect kidneys as well

Infectious Bronchitis Lesions and Transmission

Lesions:

• Foamy to thick mucus in respiratory system, thickened air sacs 

• Accumulating uric acid in organs 

High morbidity and low mortality 

• Higher mortality with co-infections 

Transmission:

• Through direct or indirect contact with infected respiratory secretions and feces

Infectious Bronchitis Treatment 

No specific treatment, may benefit from:

• Treating co-infections 

Avian Encephalomyelitis 

• Endemic tremor 

• Picornavirus, non-enveloped RNA virus 

• Reportable in NH 

Primarily affects chicks and poults 

• Vertically 

Avian Encephalomyelitis Diagnosis and Treatment 

Morbidity and mortality vary 

• Can be up to 50%

Diagnosis based on signs, microscopic lesions and serology 

No specific treatment available, can provide supportive care and cull severely affected chicks 

Vaccination is possible and performed 

Influenza/Flu

• Orthomyxoviridae

4 common types of influenza: A, B, C, D

• Differ in genetic organization, structure, host range, epidemiology, and clinical features

• Pigs and humans can contract all 4 types

Influenza Classes

Hemagglutinin (H or HA)

• Viral protein on surface that attaches to host cell

• Important for viral antigenicity

Neuraminidase (N or NA)

• Enzyme on surface that catalyzes

Naming of Influenza Viruses 

• Antigenic type 

• Host of origin (no host listed if human) 

• Geographical origin 

• Viral strain number 

• Year of first isolation 

• For influenza A, hemagglutinin and neuraminidase subtypes in parentheses 

Avian Influenza

Influenza type A

• Virus strains vary in pathogenicity:

Low path (LPAI) - majority

Highly pathogenic (HPAI) - arise from mutation of some H5 and H7 LPAI strains

Transmitted by direct and indirect contact (aerosol, fomite)

Avian Influenza Signs

Signs depend on strain and can include:

• Mild to severe respiratory signs 

• Decreased egg production 

• CNS signs and diarrhea (HPAI) 

• Death without prior signs, can occur within 24 hours of infection 

HPAI also causes edema 

Avian Influenza Diagnosis and Treatment

• Diagnosis with viral antigen testing, viral PCR, or virus isolation

• Recovered cases can be confirmed with serology

• No specific treatment (antibiotics for secondary bacterial infections)

• Biosecurity is best preventative (vaccination requires government approval)

• Zoonotic risk and reportable

Current HPAI Outbreak

Panzootic

• Asia, Europe, Americas, and Antartica

• >500 species of birds, mammals, and humans

Multiple genotypes in U.S. dairy cattle

Primary risk factor for human cases is direct contact with infected poultry

Newcastle Disease 

Like AI, viral strains of ND vary in pathogenicity 

• Low virulence NDV = lentogenic 

• Virulent NDV = mesogenic and velogenic (formerly exotic Newcastle disease) 

• Virulent NDV is a reportable disease 

Transmitted primarily by aerosol, but fecal/oral and fomites also possible 

Newcastle Disease signs and diagnosis

Clinical signs:

• Mild to severe resp signs

• ± CNS signs (headtilting, weakness, paralysis

Impossible to differentiate HPAI and vND by gross examination

Diagnosis through PCR

Vaccinations are possible

• Typically, combo vaccine with infectious bronchitis

• Not often performed in backyard flocks, unless known exposure

Potentially zoonotic (conjunctivitis, respiratory disease)