Veterinary Virology: DNA Viruses, Prions, and Retroviruses

Vocabulary practice flashcards covering veterinary DNA viruses (Herpesviridae, Parvoviridae, Poxviridae), transmissible spongiform encephalopathies (prions), and oncogenic Retroviridae (FeLV and BLV) based on lecture material.

Herpesviridae

A family of enveloped, double-stranded DNA viruses measuring $200\text{--}250\,\text{nm}$ in diameter with an icosahedral capsid; they enter cells via membrane fusion, replicate in the host cell nucleus forming intranuclear inclusion bodies, establish lifelong latency within sensory ganglia or lymphoid cells, and remain relatively labile in the environment.

Alphaherpesvirinae

A subfamily of Herpesviridae with tropism for epithelial and endothelial cells (such as skin, mucous membranes, tracheal mucosa, liver, and brain), causing active lytic infections characterized by mucosal erosions, ulcers, hepatocellular necrosis, and vasculitis.

Infectious Bovine Rhinotracheitis (IBR)

A disease of cattle caused by Bovine alphaherpesvirus 1 (BHV-1 subtype 1.1) transmitted via aerosols and direct contact; it establishes latency in the trigeminal ganglia, leading to necrotizing tracheitis, ulcerative dermatitis ("red nose"), secondary bacterial bronchopneumonia, and abortions displaying fetal multifocal hepatic necrosis with intranuclear inclusion bodies.

Equine Herpes Myeloencephalopathy (EHM)

A reportable neurologic syndrome in horses typically caused by the $D752$ strain of Equine Herpesvirus 1 (EHV-1), wherein a single nucleotide alteration confers heightened endothelial tropism, inducing severe vasculitis, thrombosis, ischemia, necrosis, and hemorrhage within the spinal cord gray matter and brain.

Canine Herpesvirus 1 (CHV-1)

An alphaherpesvirus that replicates most efficiently at temperatures below core canine body temperature; it causes fatal, generalized hemorrhagic necrotizing disease in neonatal puppies under $3\,\text{weeks}$ of age, pathognomonically characterized by multifocal renal cortical hemorrhages and necrosis alongside hepatic and pulmonary necrosis.

Feline Viral Rhinotracheitis (FVR)

An upper respiratory tract disease caused by Felid alphaherpesvirus 1 (FHV-1) that accounts for $40\%$ of feline respiratory illness; it establishes latency in the trigeminal ganglia and presents clinically with sneezing, hypersalivation, conjunctivitis, ulcerative keratitis, and epithelial intranuclear inclusion bodies.

Aujeszky's Disease (Pseudorabies)

An alphaherpesvirus infection caused by Suid alphaherpesvirus 1 (PHV-1) that replicates in oropharyngeal mucosa and travels via cranial nerves to the brain; it causes up to $100\%$ mortality and central nervous signs in suckling pigs, abortions in sows, and rapidly fatal neurologic disease with intense pruritus ("mad itch") when transmitted horizontally to secondary non-porcine hosts.

Malignant Catarrhal Fever (MCF)

A fatal, non-contagious lymphoproliferative disease of susceptible ungulates (cattle, bison, deer) caused by gammaherpesviruses (such as Ovine gammaherpesvirus 2 and Alcelaphine gammaherpesvirus 1); subclinical in reservoir hosts, it induces extensive lymphocytic perivascular cuffing, necrotizing vasculitis, mucopurulent oculonasal discharge, and bilateral corneal edema ("blue eyes").

Parvoviridae

A family of small ($18\text{--}26\,\text{nm}$), non-enveloped, linear single-stranded DNA viruses that replicate strictly in the nuclei of host cells in the S-phase of mitosis (forming intranuclear inclusions); they are exceptionally resilient in the environment against heat, solvents, pH variations, and standard disinfectants.

Feline Panleukopenia Virus (FPV)

A carnivore protoparvovirus targeting rapidly dividing host cells in feline intestinal crypts, bone marrow, spleen, and lymphoid tissue; in utero transmission causes fetal death or selective destruction of the external germinal layer of the cerebellum, resulting in neonatal cerebellar hypoplasia.

Canine Parvovirus (CPV)

A host-range mutant of FPV that emerged in the late 1970s (with modern variants 2a, 2b, and 2c) causing acute enteritis in dogs aged weaning to $6\,\text{months}$; it replicates in Peyer's patches and intestinal crypts to cause villous blunting, crypt necrosis, and hemorrhagic diarrhea, or myocardial necrosis and heart failure if contracted in utero.

SMEDI Syndrome

A reproductive failure syndrome in swine—standing for Stillbirth, Mummification, Early embryonic Death, and Infertility—caused by Ungulate protoparvovirus 1 (Porcine parvovirus); transplacental transmission leads to fetal death if infection occurs prior to fetal immunocompetence at day $70$ of gestation.

Poxviridae

The largest enveloped, double-stranded DNA viruses affecting domestic animals; uniquely capable of completing their entire replication cycle in the host cytoplasm (producing intracytoplasmic inclusion bodies) and secreting viral homologs like epidermal growth factor that stimulate marked epidermal hyperplasia and vasculitis.

Lumpy Skin Disease Virus

A reportable, foreign animal Capripoxvirus affecting cattle that produces firm cutaneous nodules progressing to sitfasts, alongside proliferative bronchiolitis and type II pneumocyte hyperplasia in the pulmonary parenchyma.

Orf Virus

A zoonotic Parapoxvirus (causing contagious ecthyma) that infects young sheep and goats; it induces severe proliferative and ulcerative epidermal lesions with crusting around the lips, muzzle, and oral mucosa, characterized histologically by ballooning degeneration, vasculitis, and intracytoplasmic inclusions.

Bovine Papular Stomatitis Virus

A zoonotic member of the genus Parapoxvirus that causes proliferative, papular, and ring-like lesions on the muzzle, dental pad, tongue, and hard palate of young calves, transmissible to human handlers as milker's nodules.

Myxoma Virus

A Leporipoxvirus whose reservoir hosts (American cottontail rabbits) develop only mild skin tumors, but which causes generalized myxomatosis—characterized by severe gelatinous swelling of periocular, facial, and genital tissues—with high mortality in European rabbits.

Prion

An infectious, non-immunogenic proteinaceous particle devoid of nucleic acid; it propagates by converting normal cellular glycoprotein ($\text{PrP}^\text{c}$, rich in $\alpha$-helices) into a protease-resistant, abnormal conformer ($\text{PrP}^\text{sc}$, rich in $\beta$-sheets) that accumulates intracellularly, leading to neuronal and neuropil vacuolation without inflammation.

Scrapie

A fatal transmissible spongiform encephalopathy affecting adult breeding-age sheep and goats; characterized by progressive behavioral changes, severe pruritus causing extensive wool rubbing and excoriation, ataxia, emaciation, and microscopic neuronal vacuolation in the medulla oblongata.

Bovine Spongiform Encephalopathy (BSE)

A fatal neurodegenerative prion disease of cattle originating in the United Kingdom in 1986 from the feeding of ruminant-derived meat and bone meal containing scrapie prions; it lacks horizontal cow-to-cow transmission and is transmissible to humans via consumption of infected tissues, manifesting as variant Creutzfeldt-Jakob disease (vCJD).

Chronic Wasting Disease (CWD)

A transmissible spongiform encephalopathy affecting free-ranging and captive cervids (mule deer, white-tailed deer, elk, and moose); clinical signs comprise marked progressive emaciation, behavioral changes, tremors, and ataxia, with horizontal transmission occurring through shedding into soil and pasture forage.

Reverse Transcriptase

An RNA-dependent DNA polymerase enzyme packaged in retroviruses that synthesizes double-stranded proviral DNA from the single-stranded RNA viral genome; due to its complete lack of 3' to 5' proofreading activity, it drives high viral mutation rates.

Endogenous Retrovirus

A proviral retroviral sequence permanently integrated into the host's germline DNA that is vertically inherited over generations, making up as much as $10\%$ of mammalian genomes; while mostly quiescent, it can recombine with infecting exogenous retroviruses to yield pathogenic, virulent recombinant strains.

Feline Leukemia Virus (FeLV)

An exogenous Gammaretrovirus of domestic cats spread horizontally through mutual grooming and saliva; it causes profound immunosuppression, non-regenerative anemia, and neoplastic transformation into lymphomas (predominantly T-cell origin) or leukemias, increasing the carrier's malignancy risk by $62\,\text{times}$.

FeLV Subgroup Variations (A, B, C, and T)

Specific pathotypes of Feline Leukemia Virus: FeLV-A is ubiquitous and directly transmissible; FeLV-B results from recombination with endogenous retroviral elements ($40\%$ of cases) and increases oncogenesis; FeLV-C arises from envelope gene mutations ($1\%$ of cases) causing fatal aplastic anemia; and FeLV-T exhibits T-cell tropism, causing severe immunodeficiency.

Enzootic Bovine Leukosis (EBL / BLV)

A Deltaretrovirus infection of adult cattle that infects B lymphocytes; transmitted through blood transfer or iatrogenically via reused needles and palpation sleeves, $30\%$ of infected animals develop persistent lymphocytosis, and $1\text{--}5\%$ develop malignant multicentric B-cell lymphoma with common predilection for the right atrium, abomasum, uterus, and lymph nodes.