Retroviruses (David Gludish) PDF

11/18/24 the retroviridae david gludish PhD, DVM [email protected] 1 retroviruses :: who cares? 2 1  11/...

11/18/24 the retroviridae david gludish PhD, DVM [email protected] 1 retroviruses :: who cares? 2 1  11/18/24 retroviruses :: many flavors immunodeficiency tumors CAEV 3 overview Introduction to the Retroviruses Structure, replication, key biological features Oncogenic retroviruses (alpha-delta retroviruses) Feline leukemia virus Avian leukosis virus Tumors Bovine leukemia virus Complex retroviruses (lentiviruses) Feline Immunodeficiency virus Equine Infectious Anemia virus Immunodeficiency Ovine Progressive Pneumonia virus Caprine Arthritis-Encephalomyelitis virus 4 2  11/18/24 learning objectives 1. Explain how oncogenic retroviruses cause tumors, and how the LTR is involved. 2. Describe the 4 different disease outcomes of feline leukemia virus in adult cats and how age determines the percentage of persistent infections. 3. List the different diagnostic methods for feline leukemia virus and what each test detects. 4. Describe the pathogenesis of feline immunodeficiency virus in relation to the cell type this virus infects. 5. State what the feline immunodeficiency virus SNAP test detects and discuss situations that can lead to false positive and negative outcomes. 5 what’s inside a retrovirus RNA: two copies of (+ sense) single stranded RNA genome (positive-sense) ENV Protein: structural proteins and viral enzymes Capsid (CA), nucleocapsid (NC), matrix (MA), and envelope (ENV); needed to make the virion reverse transcriptase (RT), protease (PR), integrase (IN); needed to replicate virus in target cells reverse transcriptase (RT) is essential to convert new genomic RNA into proviral DNA, ~30 RT proteins are packaged into the virion 6 3  11/18/24 retroviral genome: it’s packed Simple Retroviruses (only gag, pol and env genes) eg. Feline leukemia virus LTR LTR Complex Retroviruses (additional genes that regulate replication and gene expression) eg. Bovine Leukemia Virus, HIV LTR LTR 7 retroviral genome: it’s packed Long Terminal Repeat Proviral DNA loops makes a loop to integrate into host DNA and Host DNA cut is the viral transcriptional promoter Virus integrates into chromosome Final provirus arrangement 8 4  11/18/24 virion the life of a retrovirus 9 release 1 binding 8 budding receptor cytoplasm 2 fusion 7 assembly nucleus viral RNA reverse 3 transcription 5 transcription 6 translation proviral DNA 4 integration 9 key features of retroviruses 1. They undergo mutation and recombination 2. They integrate into the host cell genome 3. They (in)activate host genes near their site of integration Eg. oncogenic retroviruses 4. Generally have inefficient transmission (prolonged contact is needed) 10 5  11/18/24 the oncogenic retroviruses 1. Infect and transform cells in all classes of vertebrates (best known: cats, ruminants, chickens, and fish) 2. Cause tumors via three main mechanisms: insertional mutagenesis capture of a cellular oncogene retroviral oncogenic gene 3. Clinical signs depend on site of tumor (eg. kidney, brain, gut, etc.) 11 the oncogenic retroviruses Insertional mutagenesis: virus integrates into host genome viral promoter (LTR) will influence expression of host genes at that site if before a cellular oncogene: activation will lead to transformation if within a tumor suppression gene: disruption leads to transformation (very rare) ** Onset of tumors is usually very slow 12 6  11/18/24 insertional mutagenesis downstream oncogene tumor onco gene 13 insertional mutagenesis disrupted tumor suppressor tumor suppressor tumor 14 7  11/18/24 the oncogenic retroviruses Capture of a cellular oncogene: integration of oncogene into viral genome usually replaces some of the virus genetic material makes replication-defective or endogenous virus to replicate, cell needs to be co-infected with an intact retrovirus (helper or replication-competent/exogenous virus) also called “sarcoma” virus rare, but usually very rapidly oncogenic 15 the oncogenic retroviruses Retroviral oncogene: some viruses harbor an intrinsic oncogene v-ets (from mouse mammary tumor virus) v-src (from Rous sarcoma virus in chickens) 16 8  11/18/24 Feline Leukemia Virus General features: Simple (gamma)retrovirus of cats Common worldwide, (but decreased in recent years due to vaccination, improved diagnostics, and isolation/euthanasia of infected animals) Seroprevalence: from 6% (rural) up to 50% (urban) the more cat-cat contact, the higher the prevalence Causes lymphoma, leukemia, bone marrow suppression (immunodeficiency, anemia) Most common infectious cause of death in cats 17 Feline Leukemia Virus Pathogenesis: primary oro-nasal infection, replicates in epithelium and pharyngeal lymphoid tissues multiple outcomes are possible, depending on age of the cat, immune status, viral dose 18 9  11/18/24 PMID: 37632060 Feline Leukemia Virus antibodies 30% 30-40% 30% results A, R, D A, R, D A, R, D Progressive Regressive Abortive infection infection infection (persistent viremia) (transient viremia); (no viremia) FeLV disease Latent infection; No disease reactivation possible 19 Feline Leukemia Virus regional LN salivary gland & UG mucosa viremia shedding saliva & urine BM, gut 30% persistent viremia other LN abortive 30% 30-40% progressive regressive no viremia no disease 20 10  11/18/24 Feline Leukemia Virus: the importance of age 100% of neonatal kittens become persistently infected 90% develop tumors 30% of cats older than 4 months become persistently infected only 10-15% develop tumors Transmission: direct contact with saliva of persistently infected cat vertical transmission from persistently infected queen to kitten via placenta and milk 21 Feline Leukemia Virus Pathogenesis: Latent infection: based on diagnostic tests. circulating proviral DNA, but no viral shedding negative on all tests, except DNA PCR using blood or BM potential reactivation, transmission? de novo Feline sarcoma virus: Replication-deficient FeLV cellular oncogene (eg. myc) replaces viral pol or env gene. needs replication-competent (helper) FeLV to infect the same cell recombination & rapid cell transformation, tumor formation and death 22 11  11/18/24 Feline Leukemia Virus Clinical signs & lesions: A) Tumors: lymphoma (typically T-cell lymphomas) anatomic diversity (various clinical disease outcomes e.g. neurologic, GI, symptoms, anemia…) Feline sarcoma virus (rapid formation of tumors) 23 Feline Leukemia Virus Clinical signs & lesions: B) Immunosuppression Anemia (+/- peripheral cytopenia) Gingivitis, chronic stomatitis Queens: poor fertility, abortions Immune-mediated: glomerulonephritis, polyarthritis 24 12  11/18/24 Feline Leukemia Virus Diagnosis: 1) viral antigens ELISA: detects free p27 viral antigen (blood or saliva) viral antigen is shed from locally infected cells IFA: detects p27 viral antigen in cells (blood) viral antigen in infected bone marrow cells that are released into bloodstream 25 Feline Leukemia Virus Diagnosis: 2) viral nucleic acid DNA PCR: detects pro-viral DNA in cells (blood) not routinely used but can rule out FeLV in catteries and/or to identify ‘latent’ cats RNA PCR: detects free viral RNA (plasma, saliva) earliest detection method for FeLV reliable for viremia 26 13  11/18/24 Feline Leukemia Virus Diagnosis: 3) virus-specific antibodies of little clinical use cats frequently develop antibodies against their endogenous FeLV no convenient way to discriminate 27 Feline Leukemia Virus Control: Keep viremic cats away from other cats prevent spread to other cats protect the immune-suppressed infected cat Vaccination (inactivated vaccine, live canarypox-vectored vaccine) Catteries: regularly test to identify persistently viremic cats 28 14  11/18/24 Feline Leukemia Virus Differential Diagnosis: Feline Immunodeficiency virus (FIV) Non-viral tumors Toxoplasmosis 29 Avian Leukosis Virus General Features: Exogenous simple alpharetrovirus of chickens Worldwide distribution, but most commercial flocks are exogenous virus-free (specific pathogen-free, SPF) Disease is rare, neutralizing antibodies usually clear infection But, vertical transmission (egg/neonates) leads to persistent viremia, eventual tumors: and major horizontal transmission in flock Rous sarcoma virus: replication-defective with captured oncogene 30 15  11/18/24 Avian Leukosis Virus Pathogenesis: horizontal transmission transient viremia neutralizing antibodies rare disease vertical transmission viremia tolerance neoplasia 31 Avian Leukosis Virus Clinical signs: Lymphoid leukosis: B-cell tumors in spleen, liver, and Bursa of Fabricius. Inappetence, weakness Osteopetrosis “thick leg syndrome”: uniform diaphysial thickening of long bones of the leg Renal, mesenchymal tumors (fibroma, osteoma) Myeloid and erythroid tumors Differential diagnosis: Marek’s disease virus 32 16  11/18/24 Avian Leukosis Virus Control: Currently not a problem in USA: ALV is eradicated from primary breeder lines, most important control method Not so important in broiler flocks (only live 6 weeks), Layer flocks (esp. for vaccine production) are tested for gag antigen Most commercial flocks are ALV-resistant birds (do not possess viral receptors) No vaccine 33 Bovine Leukemia Virus General features: Exogenous complex deltaretrovirus of (esp. dairy) cattle. Causes enzootic bovine leukosis Worldwide, high prevalence, but insidious as most are subclinical Transmission: iatrogenic? (rectal exams, needle re-use, contact with infected blood), vectors (flies), ingestion of infected milk Persistent infection of B-cells, then lymphocytosis (30%) and multicentric lymphomas (1-3%) of infected cows by 4-8 years of age so most infections are subclinical 34 17  11/18/24 Bovine Leukemia Virus Diagnosis and Control: Subclinical cases are identified by serologic testing of serum or milk Test and removal programs in Europe, but not USA Due to inefficient spread in a herd: testing every 3 months and eliminating positive animals Can achieve sero-negative herd in 1- 2 years No treatment or vaccine 35 Retrovirus Flash Summary Retroviruses: enveloped RNA viruses with reverse transcriptase enzyme Integrate into host DNA (can alter cellular genes) Inefficient transmission (needs prolonged contact) Oncogenic retroviruses: tumor formation via 3 mechanisms FeLV: common (#1 infectious cause of death in cats), different clinical outcomes incl. feline sarcoma virus ALV: disease rare, unless egg or neonatal infection (tumors, osteopetrosis), Rous sarcoma virus 36 18  11/18/24 retroviruses :: many flavors immunodeficiency tumors CAEV 37 retrovirus beast mode: the Lentiviridae Chronic, long term infections: lenti (latin) means….slow Infection of CD4+ T cells (FIV, HIV): progressive immunodeficiency disease infection of monocyte/macrophages (other): cause chronic inflammatory diseases Complex retroviruses (additional genes: tat, vif, ref, nef) Transmission: very inefficient, but PERMANENT (infected for life) Infect non-dividing cells 38 19  11/18/24 Feline Immunodeficiency Virus General features: Worldwide, common (1.5% normal and 15% sick cats are infected) Domestic and wild cats can be infected with different FIV strains Many co-infected with FeLV. Overlap in clinical signs due to immunosuppression Transmission primarily through bites (outdoor cats!) Kittens: via virus shed in milk and colostrum of acutely infected queen 39 Feline Immunodeficiency Virus Pathogenesis: Infects CD4+ T cells in regional lymph nodes T cell-associated viremia: generalized lymphadenopathy, +/- fever, persists for years (long latency), eventual immunodeficiency CD4+ T cells lymphopenia: the lower the CD4/CD8 ratio, the worse the prognosis (like HIV in humans) transient or prolonged neutropenia (myelosuppression) 40 20  11/18/24 Feline Immunodeficiency Virus Diagnosis and control: SNAP test to detect antibodies available, but: many false positives (kittens have maternal antibodies, vaccinated cats) false negatives: takes 8-12 weeks to develop good antibody levels Keep cats indoors, avoid fights Treatment of symptoms (e.g. antibiotics) Vaccine: low efficacy, interference with SNAP test Anti-HIV drugs? perhaps, but only improved myelosuppression, not viral loads 41 Equine Infectious Anemia Virus General features: Worldwide, common (>70% on certain farms) Horses and other equids infected, highly variable clinical disease: no disease acute disease with death < 1 month (~30%) lifelong persistent infection, with flares of acute disease Transmission: mechanical vectors (tabanid/horse flies, stable flies, Culicoides midges) or iatrogenic Distribution/timing vector-dependent (e.g. Southern USA and regions of humidity) Not spread in milk; intrauterine vertical transmission can occur USDA Reportable disease 42 21  11/18/24 Equine Infectious Anemia Virus Pathogenesis: Lifelong cell-associated viremia in peripheral blood mononuclear cells (PBMC), +/- clinical disease Mature macrophages (spleen, lymph nodes, liver, kidney, lung, and adrenal gland) produce most of virus Waves of disease correspond with emergence of genetic variants within the host, allowing immune escape 43 Equine Infectious Anemia Virus Clinical signs: Acute signs: fever, weakness, anemia, jaundice, blood-stained feces, tachypnea, petechial mucosal hemorrhage (fatal or development of subacute infection) Subacute signs: Moderate fever, followed by recovery and lifelong infection Horses may be normal or experience recurrent disease Others develop chronic disease - mild signs of illness or persistent fever, cachexia, anemia, ventral edema Differential diagnosis: Equine viral arteritis 44 22  11/18/24 Equine Infectious Anemia Virus Diagnosis and control: Clinical signs of acute or subacute infection Coggins Test: agar gel immunodiffusion test for EIA antibodies Negative result often required for interstate transport or sale Foals nursing on infected mares may be transiently positive (antibody, NOT virus) Enzootic regions: seek insect-secure facility during vector season Management: hygiene (prevent iatrogenic transmission), quarantine new animals, test at least annually No treatment, no vaccine Isolate (euthanize) seropositive animals 45 Ovine Progressive Pneumonia Virus aka Maedi-Visna Virus General features: Associated with 2 diseases: dyspnea (Maedi, more common) encephalitis (Visna, rare) Slow onset and long incubation Inefficient transmission via aerosol droplets, milk, or iatrogenic In sheep-producing countries (except Australia and New Zealand) Persistent viremia (virus evades immune response by mutation) USDA Reportable disease 46 23  11/18/24 Ovine Progressive Pneumonia Virus aka Maedi-Visna Virus Clinical signs: exercise-intolerance, progressive dyspnea cachexia arthritis/lameness Diagnosis and control: no vaccine cull infected animals test for antibodies by ELISA, or virus by PCR USDA Reportable disease 47 Caprine Arthritis-Encephalomyelitis virus General features: Worldwide, common (up to 80% in dairy goats) Transmitted via infected milk (feeding colostrum- pooling milk to kids leads to higher infection risk) Infects monocytes/macrophages in the gut, which migrate: synovia of joints: proliferative synovitis that leads to swollen joints (goats > 1year) white matter of brain: malacia of the brain causing paralysis and death (goats 2-4 months) USDA Reportable disease 48 24  11/18/24 Caprine Arthritis-Encephalomyelitis virus Diagnosis and control: No vaccine Cull infected animals Remove kids from infected does and feed with colostrum heated to 56ºC, then pasteurized goat/cow milk or milk replacer Test for antibodies by ELISA, or virus by PCR USDA Reportable disease 49 Lentivirus Flash Summary immunodeficiency characterized by chronic, long term infections very few treatment options; no (or ineffective) vaccines FIV: very common in cats, frequent co-infection with FeLV, isolate EIAV: arthropod transmitted, highly variable reportable clinical disease in horses, anemia, cull or isolate OPP: dyspnea (common) and encephalitis (rare), reportable, cull CAEV: very common in dairy goats, synovitis and paralysis, reportable, cull 50 25