Veterinary Virology: Poxviridae, Adenoviridae, Papillomaviridae, Asfarviridae, Iridoviridae, and Herpesviridae

Comprehensive review flashcards covering Poxviridae, Adenoviridae, Papillomaviridae, Asfarviridae, Iridoviridae, and Herpesviridae.

What is unique about the replication site of poxviruses compared to most other DNA viruses?

Poxvirus replication occurs entirely within the cytoplasm of the host cell in localized structures known as cytoplasmic "virus factories."

What morphological characteristics describe poxvirus virions under negative-stain electron microscopy?

They are large ($220\text{--}450 \times 140\text{--}260\,\text{nm}$), pleomorphic, typically brick-shaped virions with complex symmetry, surface tubular/globular projections, a lipoprotein membrane, and characteristic lateral bodies.

What are the six chronological stages in the development of cutaneous poxvirus lesions?

Macule, Papule, Vesicle, Pustule, Crust, and Scar.

What are the two subfamilies of the family Poxviridae and their respective host types?

Chordopoxvirinae, which infect vertebrates, and Entomopoxvirinae, which infect insects.

What animal species serves as the true primary reservoir for Cowpox virus?

Rodents serve as the primary natural reservoir hosts (cattle are accidental spillover hosts despite the virus's name).

How do the clinical manifestations of Cowpox virus differ between cattle and cats?

In cattle, disease is relatively rare and localized to the teats and udder; in cats, infection is more severe, often beginning as a solitary necrotizing skin lesion that can progress to generalized systemic disease.

Which two major clades comprise Monkeypox virus (MPXV), and how do their clinical severity and epidemiology differ?

Clade I (subclades Ia and Ib) is native to Central Africa and historically causes more severe disease; Clade II (subclades IIa and IIb) is native to West Africa and is associated with milder disease, with Clade IIb driving the 2022 global human outbreak via close physical and sexual contact.

What disease of sheep and goats is shown presenting with proliferative, highly vascularized, and easily bleeding scabby lesions at the mucocutaneous junction of the lips?

Orf (also known as contagious ecthyma or contagious pustular dermatitis), caused by Orf virus (genus Parapoxvirus).

What traditional vaccination technique is utilized to protect sheep flocks against Orf virus prior to lambing?

Axillary scarification, which creates a localized, controlled, abortive infection that induces temporary protective immunity.

What distinctive gross lesion morphology is characteristic of Pseudocowpox virus infection on bovine teats?

"Ring"- or "horseshoe"-shaped scabs.

What are the two clinical forms of Fowlpox, and what pathological lesions characterize the more fatal form?

The cutaneous (dry) form produces papules and pustules on unfeathered skin (comb, wattles, eyelids); the diphtheritic (wet) form produces necrotic pseudomembranes in the mouth, pharynx, larynx, and trachea that can lead to death by asphyxiation.

Why are avipoxviruses, such as canarypox virus, frequently utilized as recombinant vaccine vectors in mammals?

They can enter mammalian cells and express foreign recombinant antigens to induce an immune response, but they cannot undergo productive viral replication in mammalian hosts.

What viral genus contains the most economically important poxviral livestock pathogens, and what are its three major diseases?

Genus Capripoxvirus, which causes Sheeppox, Goatpox, and Lumpy Skin Disease (LSD).

What is the primary mode of transmission for Lumpy Skin Disease virus among cattle?

Mechanical transmission by blood-feeding arthropod vectors (biting insects).

How does Myxoma virus infection differ between its natural New World rabbit hosts and European rabbits (Oryctolagus cuniculus)?

In South American wild rabbits (Sylvilagus spp.), it causes localized, benign fibromas; in European rabbits, it causes severe, generalized myxomatosis characterized by blepharoconjunctivitis, gelatinous subcutaneous swellings, and mortality approaching $100\%$.

What virion architecture and structural components characterize the family Adenoviridae?

Non-enveloped icosahedral virions ($70\text{--}90\,\text{nm}$) containing a linear double-stranded DNA genome, with capsomers consisting of hexons and projecting penton fibers.

Where does adenovirus replication occur, and what characteristic histological feature does it produce?

Replication occurs in the nucleus, producing characteristic basophilic intranuclear inclusion bodies.

What is the immunological mechanism behind corneal oedema ("blue eye") seen during recovery from Canine Adenovirus 1 (CAV-1)?

It is a Type III hypersensitivity reaction resulting from the deposition of viral antigen-antibody immune complexes in the corneal endothelium.

Why is modified-live Canine Adenovirus 2 (CAV-2) used in canine core vaccines instead of CAV-1?

CAV-2 shares antigenic cross-reactivity and provides cross-protection against CAV-1 without inducing the adverse immune-complex-mediated corneal oedema ("blue eye") associated with CAV-1 vaccines.

In which specific equine population do Equine Adenoviruses (EAdV-1 and EAdV-2) produce severe, fatal disseminated disease?

Arabian foals suffering from inherited severe combined immunodeficiency (SCID).

What disease is caused by Fowl aviadenovirus 4 (FAdV-4) in commercial broilers, and what are its post-mortem signs?

Hepatitis-hydropericardium syndrome (HHS), characterized pathologically by hydropericardium (fluid accumulation in the pericardial sac) and hepatomegaly.

What is the historical origin of Egg Drop Syndrome Virus introduction into commercial chicken flocks?

Waterfowl are the subclinical natural reservoir; the virus originally contaminated commercial poultry vaccines that were propagated in duck cell cultures.

What gross pathological lesion is pathognomonic for Haemorrhagic Enteritis of Turkeys caused by Turkey adenovirus 3?

Marked splenomegaly (enlarged, mottled "marble spleen") accompanied by severe intestinal mucosal haemorrhage.

What type of nucleic acid genome and cell tropism characterize the family Papillomaviridae?

Non-enveloped, circular double-stranded DNA (dsDNA) genome with a strict tropism for the basal squamous epithelial cells of skin and mucous membranes.

Ingestion of which toxic plant acts synergistically with bovine papillomaviruses (BPV-2 and BPV-4) to induce squamous cell carcinomas in cattle?

Bracken fern.

What viral etiologic agents are associated with Equine Sarcoids, and what is their clinical behavior?

Bovine papillomaviruses types 1 and 2 (BPV-1 and BPV-2); they cause locally invasive, non-metastasizing fibroblastic skin tumors that frequently recur after excision.

What benign viral condition is shown presenting with multi-lobulated, "cauliflower-like" proliferative lesions on the buccal mucosa and tongue of a young dog?

Canine oral papillomatosis, caused by Canine papillomavirus.

What organism causes fibropapillomatosis in sea turtles, which is a common taxonomic point of confusion?

A herpesvirus (Chelonid herpesvirus 5), not a papillomavirus.

What is the taxonomic classification, virion structure, and genomic nature of African Swine Fever Virus (ASFV)?

Family Asfarviridae, genus Asfivirus; it is a large ($~200\,\text{nm}$), enveloped, icosahedral virus with an internal lipid membrane and a linear double-stranded DNA genome ($170\text{--}194\,\text{kbp}$).

What unique biological distinction does African Swine Fever Virus hold among all known DNA viruses?

It is the only known DNA virus that functions as a biological arbovirus (transmitted and replicating within an arthropod vector).

What cell types represent the primary cellular targets of African Swine Fever Virus replication?

Monocytes, macrophages, and endothelial cells.

What wildlife species maintain African Swine Fever Virus in its native sylvatic transmission cycle in Africa?

Common warthogs (Phacochoerus africanus), which experience inapparent subclinical infection or transient juvenile viraemia, and soft ticks of the genus Ornithodoros.

What gross lesion shown in this porcine kidney is classically described as a "turkey egg" appearance during African Swine Fever Virus infection?

Extensive petechial and ecchymotic cortical haemorrhages.

What major post-mortem splenic lesion helps distinguish African swine fever on necropsy?

A markedly enlarged, congested, dark-purple, and friable (infarcted) spleen.

How many pigs died or were culled in China as a result of the African swine fever epidemic starting in 2018?

As many as $225\,\text{million}$ pigs, representing nearly $25\%$ of the entire global pig population.

What potential sylvatic vector association was identified in Florida gopher tortoise burrows regarding African swine fever transmission risks in the USA?

Contact between invasive wild pigs (Sus scrofa) and the native soft tick vector Ornithodoros turicata americanus.

What vertebrate classes serve as hosts for the family Iridoviridae?

Ectothermic vertebrates and invertebrates, primarily fish, amphibians, reptiles, and arthropods.

What clinical and pathological outcomes distinguish Ranavirus infections in amphibians?

Severe systemic epizootics with high mortality, characterized by cutaneous ulceration, generalized subcutaneous edema, and multifocal petechial haemorrhages and necrosis across internal visceral organs.

What cellular mechanism causes the formation of "lymphocysts" in fish infected with Lymphocystivirus?

Marked, extreme hypertrophy of dermal and connective tissue fibroblasts resulting from virus-mediated arrest of host cellular division.

What clinical signs and necropsy findings characterize Megalocytivirus infections in marine and freshwater fish?

Lethargy, severe anemia, branchial (gill) haemorrhages, marked splenic enlargement, and large basophilic cytoplasmic inclusion bodies in infected cells.

What is the defining biological hallmark of all herpesviruses following primary infection?

The establishment of lifelong latency with the capacity for periodic reactivation (recrudescence) and shedding upon immunosuppression or stress.

Which three families comprise the order Herpesvirales?

Alloherpesviridae (infecting fish and amphibians), Malacoherpesviridae (infecting molluscs such as oysters and abalone), and Orthoherpesviridae (infecting mammals, birds, and reptiles).

Where in the host cell does herpesvirus replication and nucleocapsid assembly occur?

Within the host cell nucleus, producing eosinophilic or basophilic intranuclear inclusion bodies.

What are the primary distinguishing features of the three subfamilies of Orthoherpesviridae regarding latency site?

Alphaherpesvirinae establish latency primarily in sensory ganglia (neurons); Betaherpesvirinae establish latency in secretory glands, kidneys, and lymphoreticular cells; Gammaherpesvirinae establish latency primarily in lymphocytes (T or B cells).

What severe pathology characterizes the acute form of Avian Infectious Laryngotracheitis (ILT)?

Severe haemorrhagic laryngotracheitis with mucosal necrosis, fibrinous diphtheritic exudate, and bloody mucus obstructing the tracheal lumen, leading to death by asphyxiation.

How is Marek's Disease Virus (MDV) transmitted among chickens?

By inhalation of contaminated feather dander and poultry dust shed from infected feather follicle epithelial cells.

What pathological lesions and clinical syndromes are caused by Marek's Disease Virus?

Neoplastic transformation of $CD4^+$ T lymphocytes leading to visceral T-cell lymphomas, enlargement of peripheral nerves (brachial and sciatic nerves causing asymmetric leg/wing flaccid paralysis), and grey iris with pupillary irregularity ("ocular lymphomatosis").

How does the commercial in ovo Marek's disease vaccine operate regarding infection and virus shedding?

It prevents the development of clinical disease and lymphoma formation, but it does not prevent field virus infection, replication, or shedding into the environment.

What diagnostic technology enables differentiation between cattle vaccinated against Bovine Herpesvirus 1 (BHV-1) and those infected with wild-type virus?

DIVA (Differentiating Infected from Vaccinated Animals) marker vaccines that have a glycoprotein E ($\text{gE}$) gene deletion, evaluated using companion $\text{gE}$ antibody detection ELISAs.

What clinical syndrome caused by Bovine Herpesvirus 2 (BHV-2) is an important differential diagnosis for capripoxvirus infections?

Pseudo-lumpy skin disease (the other major syndrome caused by BHV-2 being bovine ulcerative mammillitis).

What is the primary underlying pathological lesion responsible for both late abortion storms and myeloencephalopathy (EHM) in Equine Herpesvirus 1 (EHV-1) infection?

Endotheliotropic infection leading to systemic endothelial necrosis, vasculitis, and thrombosis in uterine and CNS blood vessels.

How do Equine Herpesvirus 1 (EHV-1) and Equine Herpesvirus 4 (EHV-4) differ clinically?

EHV-4 is primarily restricted to respiratory mucosal epithelium causing upper respiratory tract disease ("rhinopneumonitis") in foals, whereas EHV-1 causes severe abortion storms and paralytic myeloencephalopathy (EHM) in addition to respiratory signs.

Why is Canine Herpesvirus 1 (CHV-1) infection rapidly fatal in neonatal puppies younger than 3 weeks old ("fading puppy syndrome"), but mild or inapparent in adults?

CHV-1 replicates optimally at lower temperatures ($<37^\circ\text{C}$); neonatal puppies possess poorly developed thermoregulation, allowing unchecked systemic hypothermic viral dissemination that causes widespread necrotizing vasculitis and haemorrhage.

What viral infection is responsible for the fatal neurotropic condition in aberrant hosts (such as cattle, dogs, and cats) characterized by frenzied self-mutilation known as "mad itch"?

Pseudorabies (Aujeszky's disease), caused by Suid alphaherpesvirus 1 (SuHV-1), for which pigs are the natural reservoir.

What viral entity causes Porcine Cytomegalovirus (PCMV) infection in young piglets, and what is its classic clinical presentation?

Suid betaherpesvirus 2; it produces inclusion body rhinitis characterized by sneezing, snuffling, catarrhal nasal discharge, and marked cytomegaly with intranuclear inclusions in nasal mucosal glandular epithelium.

What are the two major epidemiological forms of Malignant Catarrhal Fever (MCF) and their respective subclinical natural reservoir hosts?

Sheep-associated MCF (caused by Ovine herpesvirus 2 [OvHV-2], maintained subclinically in domestic sheep) and Wildebeest-associated MCF (caused by Alcelaphine herpesvirus 1 [AlHV-1], maintained subclinically in wildebeest).

What microscopic pathological lesion is pathognomonic for Malignant Catarrhal Fever in affected cattle and deer?

Widespread lymphocytic vasculitis and perivascular mononuclear cuffing associated with marked T-lymphocyte infiltration.

Why do cattle clinically sick with Malignant Catarrhal Fever not pose a transmission risk to other co-housed cattle?

Cattle are dead-end aberrant hosts that shed little to no infectious cell-free virus; transmission occurs strictly from the wildlife/livestock reservoir species (sheep or wildebeest).

What is the causative agent and primary gross lesion of Koi Herpesvirus Disease (KHVD)?

Cyprinid herpesvirus 3 (CyHV-3, family Alloherpesviridae); it is characterized by severe, patchy gill necrosis and mottled gill discolouration.