Herpes

Front 1

Describe the general features of Herpes viruses

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-enveloped DNA viruses with icosahedral symmetry
-replicate in nucleus
-labile in the environment
-cause diseases of the respiratory, reproductive, and nervous systems; may cause cell transformation in some species
-latency is a common outcome of infection with these viruses

Front 2

Describe the virus properties, pathology & clinical signs, immune response, epidemiology, diagnosis & control of Herpes virus.

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♦PROPERTIES
-large, ENVELOPED viruses with an icosahedral capsid that encases a single, double-standed molecule of DNA
-the envelope is a lipid bilayer membrane, which has glycoprotein projections that are important in the attachment of the virus to host cells
-fragile in the external environment, surviving ony a few hours
-require close contact, often apposition of mucosal surfaces, for efficient transmission between individuals
-when large numbers of susceptible animals are grouped together, such as in cattle feedlots, catteries, or intensive poultry farms, aerosols of droplets can efficiently spread infection
-survival of herpes viruses from generation to generation is facilitated by life long infection of the host, which is characterised by latency and occasional or frequent recrudescence with viral shedding
-usually latent in cells of CNS, particularly nerve ganglia

♦PATHOLOGY & CLINICAL SIGNS
-range from local vesicular lesions (e.g. EHV3 which causes coital exanthema in horses) to encephalitis (e.g. porcine herpes virus 1 in cattle) to abortion (EHV 1 in horses), neoplastic transformation of cells to form lymphoid tumors (Marek's disease virus in poultry) and generalised fatal neonatal disease (Canine herpesvirus 1 and EHV 1)
-lifelong persistence in animal

♦IMMUNE RESPONSE
-both humoral and cell-mediated immune response follow initial infection, but in spite of this persistent infection occurs
-vaccines for Marek's disease are the most successful and are either live attenuated or an antigenically related herpes virus from another species
-Marek's vaccine helps prevent development of cancer
-vaccines are available for EHV 1 and 4 and a subunit vaccine (contaning surface glycoproteins from disrupted virions) has been successfully used as part of eradication schemes for porcine herpesvirus 1 (Aujeszky's disease)
-herpes virus evades the immune system by spreading from cell to cell by causing fusion of the cell membrane
-infected cells if they display virus-specific antigens on the surface may be destroyed by ADCC or CD 8 T cells
-some herpes viruses cause the cell to release molecules that confuse the immune system
-latently infected animals can be readily detected by testing for the presence of antibody in serum
-if you wish to eradicate herpes virus you need to detect infected animals by testing serum for antibody and removing all infected animals

♦EPIDEMIOLOGY
-important features of the virus are life long latency with intermittent shedding of infectious virus and the fragile nature of the virus in the external environment
-the source of virus for infection of susceptible animals will be an infected animal
-virus is shed by the infected animal but can only last for hours to a few days in the environment
-aerosol spread can occur over short distances (e.g. when stocking density is high)
-stressful situation (ie. nutrition, transport etc.) can cause latently infected animals to shed the virus

♦DIAGNOSIS
-definitive diagnosis is based on isolation and identification of the virus (or PCR for the presence of viral DNA), detection by microscopic examination of typical intranuclear inclusion bodies in affected tissues, detection of specific viral antigen in tissues (e.g. by immunocytochemical staining with labelled specific antibody), detection of specific antibody in serum of affected animals and a rise in titre between acute and convalescent serum samples
-selection of the most appropriate test and its interpretation depends on which tissues are likely to contain the virus

♦CONTROL
-achieved by selection of the most appropriate options for the particular situation, including vaccination, stress minimization, segregation of infected animals from susceptible animals (e.g may be age related so separate based on age groups), environmental hygiene to remove infectious virus that is present on fomites, decreasing stocking density to minimize spread, quarantine of introduced animals, vaccination etc.

Front 3

EHV 1 & EHV 4 infection

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-infections with these viruses are acquired early in life and are common in all horses populations
-EHV 1 is associated with both occasional single abortions in mares and also outbreaks of abortioins in which many mares in a group may abort in a space of a few weeks
-EHV 4 is occasionally associated with single abortions, not epidemics, and is a common cause of respiratory disease in weanlings, yearlings and horses in training
-an EHV1 & EHV4 inactivated vaccine is available
-latency is a feature, usually in trigeminal ganglion
-few of these viruses are associated with myeloencephalitis, typically ascending paralysis

Front 4

Bovine Herpesvirus 1

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-common virus of cattle that is associated with respiratory disease and genital lesions (pustular vulvovaginitis)
-because of cattle feedlots it has become a more significant cause of respiratory disease often followed by bacterial pneumonia
-some stains cause abortion in cattle
-attenuated and inactivated vaccines are available overseas

Front 5

Bovine Herpesvirus 2

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-causes lesions of the teats of dairy cattle (bovine herpes mammillitis) and also pseudo-lympyskin disease
-present in Australia but infrequently identified
-causes generalised infection and swelling of skin in calves

Front 6

Porcine Herpesvirus 1 (Aujeszky's disease)

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-manifests as respiratory disease in weaned pigs, abortion in pregnant sows, and death in piglets due to disseminated infection
-many other species are susceptible to infection, which is manifested as a nervous disease with intense itching and self mutilation ("mad itch" or pseudorabies)
-usually fatal in other species
-when infection first enters a piggery the range of clinical signs is often clearly apparent, but as herd immunity develops the signs are more subtle

Front 7

EHV 3

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-equine coital exanthema
-lesions on genitals

Front 8

Bovine Herpesvirus 5

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-causes encephalitis in calves
-mostly in Queensland

Front 9

Canine Herpesvirus 1

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-associated with mismothering, body temperature drops, and virus proliferates
-if body temperature remains normal, don't see infection
-infection of pups <4 weeks of age can result in generalised hemorrhagic disease with mortality approaching 100%
-at post mortem see hemorrhages in adrenal gland, kidney, and GI tract
-inclusion bodies in hepatocytes

Front 10

Feline Herpesvirus 1

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-causes acute disease of the upper respiratory tract of cats of many species
-in young kittens the infection may be atal due to extensive bronchopneumonia
-ocular discharge and corneal and lingual ulcers re common
-vaccines are available for control of this infectious disease and form a usual component of a standard vaccination program for cats

Front 11

Gallid Herpesvirus 1

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-common & serious infection of poultry characterized by hemorrhagic tracheitis
-mortality of 70%
-chickens cough and create and aerosol of the virus
-can use a live attenuated vaccine to minimise severity of the disease (can't prevent the disease)

Front 12

Gallid Herpesvirus 2

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-infection of poultry with this virus results in the development of lymphoid tumors that result in death of birds
-known as Marek's disease
-controlled by live virus vaccines (either heterologous vaccine [turkey herpesvirus] or attenuated strains)
-virus shed in feather dander
-disease results from the infection of T lymphocytes and their transformation into lymphoblasts that proliferate and invade nervous tissue
-usually invades nervous tissue on one side of the body
-Marek's disease virus carries in its genome an onc gene that become incorporated into the genome of infected cells and is responsible for their transformation into neoplastic cells
-vaccines strains of the virus do not contain and onc gene

Front 13

Alcelaphine Herpesvirus 1

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-infection of cattle with this virus results in a fatal lymphoproliferative disease - malignant catarrhal fever
-in africa the virus is present as an inapparent infection in wildebeest
-epidemics in cattle ocur when they become infected following contact with these inapparently infected animals, particularly when wildebeest are calving
-diagnosis is based on characteristic histological lesions with necrosis of blood vessel walls especially in the brain & kidney