Prelim 2 Viruses - Herpesviruses I

General Features:
Canine

Alphaherpesvirus

Common infection (6-100%)

Uncommon disease, usually no CS in adults w/ latent infection Pups < 2wks age with low body temps → high mortality, 80-100%

Concern to breeders of purebred dogs

General Features of Canine Herpes Virus 1 (CHV-1)

Lesions:

(dogs)
In necropsy of dead puppies—

Enlarged LN, swollen spleen,

Focal necrosis and hemorrhages (Lung, liver, adrenal glands, kidneys, GIT; possible in eyes, CNS)

Lesions of CHV-1

Diagnosis:

(Dogs)

CS, lesions

Histopath: Intranuclear inclusion bodies

DDx for “puppy death”:

Canine parvovirus, Infectious canine hepatitis (CAV-1, would see thickened gallbladder), Canine distemper (wouldn’t see quick & sudden death)

Diagnosis of CHV-1

Tx and Control:
(dogs)
Unrewarding to tx with antivirals in systemically infected pups, poor prognosis due to organ damage
Adult dogs usually mild CS and self-limited
No vaxx in US
Keep pups warm up to 4 wks old

Tx and Control of CHV-1

General Features:
Feline
Alphaherpesvirus
Infection very common
Causes feline viral rhinotracheitis (FVR)
Spread thru oral and nasal secretions
Coinfections common w/ feline calcivirus, both part of FRDC)

General Features of Feline Herpes Virus 1 (FHV-1)

Pathogens of the Feline Respiratory Disease Complex (FRDC)

FHV-1, Feline calcivirus, Chalmydia felis, Mycoplasma felis

Pathogenesis:

(cats)
1* infection of mucosal/epithelial surfaces (resp. epithelium, corneal epithelium) → Massive cell death → ulcers, inflammation, sneezing, clear discharge

2* bacterial infection → Mucopurulent discharge

Latent virus in trigeminal ganglia, possibly other sites

Pathogenesis of FHV-1

CS:

(cats)
Immune animals: Mild-no CS
1* infection: Conjunctivities, sneezing, oral & nasal discharge from clear to mucopurulent, Ulcers of nasal/oral epithelium, fever, depression, anorexia
Occasionally can cause abortion

Clinical Signs of FHV-1

Diagnosis:
(cats)
Clinical sigs and lesions— corneal ulcers uncommon, but usually ____
DDx:

Calcivirus (more lingual ulcers)
Chlamydia felis (Conjunctivitis)

Can do Virus Isolation, but only done when cattery is at stake

Virtually every animal is seropositive

Diagnosis of FHV-1

Tx:
(cats)
Symptomatic, supportive care
Broad spectrum Abx helpful against 2* bacterial infections
Nasal & ocular discharges removed freq. for comfort
Systemic tx rarely effective, many acyclovr derivatives are toxic to cats
Famcyclovir tolerated
Tx of corneal lesions is multifaceted, tailored to pt and owner → usually antiviral drugs to inhibit viral DNA replication

Treatment of FHV-1

Control:
(cats)
Vaccination
1) Modified live → Parenteral or Oronasally (latter difficult to give to kittens, but good immunity w/o interference from maternal immun.)
2) Inactivated → Parenteral use only 

Sick animals in catteries are threat to others → Remove, isolate, handle last 
Hygiene

Control of FHV-1

General Features
Swine
Alphaherpesvirus
AKA Pseudorabies virus (PRV) or Augeszky’s disease
Important disease of swine
Pigs are natural host
Other domestics susceptible, usually fatal in alt. host animals
Successfully eradicated from most commercial swine herds → no vaccination → herds highly susceptible
Common in feral swine, often w/o CS
Reportable disease

General Features of Suid herpesvirus 1 (SHV-1)

PRV was successfully eradicated from most US commercial swine herds, so they are no longer vaxx, but this leaves herds highly susceptible should future outbreak occur. Is endemic in feral swine and often w/o CS

Implications of current SHV-1 status in US

Pathogenesis:
(swine)
Infection → Upper resp. disease → Cell-assoc. viremia (Monocytes) → Spinal cord (Neuro disorders) and/or placenta (abortion) → Latency in trigeminal ganglia

Pathogenesis of SHV-1

Cell-Associated, monocytes

What type of viremia is characteristic of SHV-1?

CS:
(swine)

In immunologically naiive pigs
Piglets < wk: Neuro signs (trembling, paddling), fever, anorexia, rapid death (high mortality)
Older piglets: Resp problems, vomiting, similar symptoms, lower mortality
Adult pigs: Mild-no symptoms, Reproductive disorders (abortion, infertility, fetal mummfication), resp/neuro disorders
Feral swine: Asymptomatic

CS of SHV-1 in Swine

CS:
Cows: Bellowing, mad itch, death
Horses: Mad itch, death (VERY rare)
Dogs: Excessive lacrimation, howling, seizures, death
Cats: Seizures, sudden death
Rodents: Seizures, death
Humans: No CS, unsure whether susceptible

CS of SHV-1 in Cows, Horses, Dogs, Cats, Rodents, Humans 

Dx:
(swine)
CS
Virus isolation

Diagnosis of SHV-1

Control:
(swine)
No vaxx in US
Reportable
In endemic countries (Europe), Marker vaccines used

Control of SHV-1

Ie, in SHV-1, the viral strain used in the vaccine lacks viral glycoprotein E. If an animal is seropositive for gE antibodies, it indicates a WT virus infection

Explain how Marker Vaccines work

General Features
Poultry
Alphaherpesvirus
AKA Infectious Laryngotracheitis Virus (ILTV)
More common in backyard flocks
Morbidity 100%
Mortality is strain dependent, 10-70%
Also infects peasants
Reportable

General Features of Gallid Herpesvirus 1 (GaHV-1)

Pathogenesis:
(chickens)
1* infection of resp. epithelium (corneal epithelium) → Replication in trachea → Necrosis → Erosion, ulceration, hemorrgages in trachea

No clear evidence of viremia
Latency in trigeminal ganglia, unknown cell type
Freq. reactivations during stress

Pathogenesis of GaHV-1

CS:
(chickens)
Nasal discharge, sneezing
Coughing, gasping, labored breathing
Conjunctivitis
Depression, dec. egg production

Clinical Signs of GaHV-1

Lesions:
(chicken)
Sloughing of epithelium + clotted blood → Diphtheritic membranes → Occlude bronchi, syrinx, trachea

Lesions of GaHV-1

Dx:
(chickens)
CS
Necropsy: Presence of blood, mucus, caseous yellow exudates in trachea 
Lab techniques: PCR, virus isolation, Histo (intranuclear inclusions → Intracytoplasmic inclusions caused by diphtheritic form of fowlpox)

Diagnosis of GaHV-1

Control:
(chickens)
In endemic areas: Biosecurity, vaxx
Modified live vaxx or recombinant fowlpox vaxx

Biosecurity > vaxx in high production units

Control of GaHV-1

General Features:
Poultry
Alphaherpesvirus
Aka Marek’s Disease Virus (MDV)
Ubquitous avian infection
Highly lymphotropic, cause tumors

General Features of Gallid Herpesvirus 2 (GaHV-2)

Turkeys
Avirulent strain related to MDV, used as MDV Vaxx in chickens

Importance of Turkey Herpesvirus (HVT)

Pathogenesis:
(chickens)
Inhalation of dander-bearing virus, 4 phases

1) Early productive-restrictive virus infection of B cells
2) Latent infection in activated CD4+ T cells (Long term carriers)
3) Reactivation in CD4+ T cells with productive-restrictive replication and permanent immunosuppression
4) Proliferative phase, involving latently infected T cells → Neoplastic transformation (lymphoma) + Productive infection of feather follicle epithelium (transmission)

Pathogenesis of Merek’s (GaHV-2)

CS
(chicken)
Variable, from transient paralysis to persistent neurological dz (ataxia), depression, dec. egg production, atherosclerosis, early mortality

Clinical Signs of Merek’s (GaHV-2)

Lesions
(chicken)
Neoplasms
Irregular pupil margin
Thickened (sciatic) nerves
Enlarged feather follicles (Skin leukosis, seen after defeathering)

Lesions of Merek’s (GaHV-2)

Dx:
Typical CS, necropsy, rarely need viral isolation

DDx:
Avian leukosis, but rarely see paralysis, iris lesions, intranuclear inclusions in avian leuk.

Diagnosis of Merek’s (GaHV-2)

Control:
(chicken")
Vaxx w/ modified live in ovo/ SC 1 day age

Maternal immunity lasts 3 wks, does not interfere w/ effective vaxx

Control of Merek’s (GaHV-2)

High mortality in poorly managed pups

Take home: CHV-1

Part of the feline resp. disease complex

Take home: FHV-1

Important economic dz of swine worldwide, reportable

Take home: SHV-1

High biosecurity measures limit need for preventative vaxx

Take home: GHV-1