Equine Viral Diseases Lecture Notes PDF

Equine Viral Diseases  Equine Viral Diseases Equine Herpes Virus (EHV) infection Equine Encephalomyelitis Equine Influenza Equine Infectious Anemia West Nile Virus Equine Viral Arteritis Rabies Hendra Virus infection African Horse Sickness  Equine Herpes Virus Speci...

Equine Viral Diseases  Equine Viral Diseases Equine Herpes Virus (EHV) infection Equine Encephalomyelitis Equine Influenza Equine Infectious Anemia West Nile Virus Equine Viral Arteritis Rabies Hendra Virus infection African Horse Sickness  Equine Herpes Virus Species specific Three subfamilies: alpha, beta (none in horses), gamma 9 documented strains, but only 5 affect domestic horses Only EHV1, EHV3 and EHV4 commonly cause diseases in horses 1. EHV-1 () - Subtype 1 of EHV1 a. Rhinopneumonitis (respiratory form) b. Abortion c. Birth of weak foals d. Peracute vasculitis – lungs; fatal in adults e. Neurological  EHV-1 EHV-1 is common throughout the world and most important viral cause of abortion in horses Can be sudden and deadly High temperature “Fulminating” respiratory disease May see all 5 of the syndromes at once Horses of all ages are affected Mares 3-9 months pregnant most susceptible Abortion storm virus first identified in the 1940s  EHV1 Mode of Transmission Horse to horse by direct contact, nasal secretion, reproductive discharge, placenta or aborted fetus Short-distance airborne spread also possible Clinical Signs Viral incubation for 2-10 days 1. Fever (38.8 to 41.6’C for 1-7 days) 2. Malaise, depression, anorexia 3. Congestion and serous discharge from the nostrils 4. Swollen lymph nodes  EHV-1 5. Mild incoordination to severe ataxia, paresis and paralysis 6. Loss of bladder tone, tail tone, skin sensation in hind limbs Diagnosis 1. Fluorescent antibody, PCR 2. Virus isolation from fetal tissues 3. Differential diagnosis with EI, EVA and other resp dss Treatment 1. Supportive nursing  EHV-1 2. NSAIDs to control malaise and fever; will encourage eating 3. Fluid therapy if dehydrated 4. Antibiotics to prevent secondary bacterial infection (especially if respiratory disease); Valacyclovir 30mg/kg,PO, bid 5. Corticosteroids to reduce nerve inflammation If horse remains standing, prognosis is good Prevention 1. Vaccination at 5, 7 and 9 month of gestation  EHV1 2. Prevent exposure to other horses attending shows or other equine events  EHV3 2. EHV-3 Venereal disease Equine Coital Exanthema Rare but important Doesn’t cause death Self-limiting Characteristic lesions on genitalia of stallions and mares  EHV4 3. EHV-4 Subtype 2 of EHV1 Respiratory infection only (“Rhino”); rhinopharyngitis and rhinotracheitis Non-fatal, rarely results in abortion Severe, widespread outbreaks in young horses; foals → 3 years old in training Not a problem in older horses (develop immunity)  EHV2/EHV5 4. EHV-2 and EHV-5 Gamma family “Ubiquitous” but rarely causes disease Found in nearly 100% of healthy foals Can cause problems in the following diseases: 1. EHV2 - Herpetic keratoconjunctivitis in young foals; may act as a forerunner that leads to Rhodococcal infection (through immune suppression) 2. EHV5 – equine multinodular pulmonary fibrosis (EMPF); in middle-aged horses  EHV5 Has emerged as a pathogen (EMPF) Clinical Signs 1. Tachycardia, tachypnea, increased inspiratory effort and poor body condition 2. Wheezing and crackling, maybe mistaken as heaves Associated with lymphoproliferative diseases and lymphoma Diagnosis 1. CBC – neutrophilic leukocytosis with or without hyperfibrinogenemia and anemia  EHV5 2. Thoracic radiographs 3. Virus-specific PCR test on pulmonary secretions or percutaneous lung biopsy sample Prognosis for survival is approx. 50% Treatment 1. Valacyclovir 30 mg/kg, PO, tid and/or acyclovir 10ng/kg, IV in 1L of isotonic crystalloid fluid as infusion over 1 hour, bid for 2 days 2. Doxycycline – 5 to 10mg/kg, PO, 1-2 times daily; for 2ndary bacterial infection and anti-inflammatory properties  EHV5 3. Corticosteroid – 0.08-0.1 mg/kg IV very 24-48 hours; reduction ofpulmonary cytokines and inflammatory mediators; cause immunosuppression and enhance viral replication Diagnosis EHV PCR and isolation of virus from nasopharygeal swabs and blood samples during early stage of infection Treatment Anti-inflammatory drugs IV fluid Antibiotics for secondary bacterial infection Prevention Vaccination Control Biosecurity practices Equine Arboviral Encephalomyelitis Arthropod-borne viruses that cause central nervous system dysfunction and moderate to high mortality Caused by alphaviruses of the family Togaviridae Endemic in North, South and Central America Western (WEE) - 20-50% fatal Eastern (EEE) - 50-90% fatal Venezuelan (VEE) - 50-75% fatal Highland J virus, Everglades virus Semliki Forest virus – East and West Africa Japanese encephalitis virus (JEE/Flavivirus) – Asia, India, Russia, Western Pacific – 35-45%  Madariaga (MADV/Flavivirus) in South America and Caribbean WNV (Flavivirus) in Africa, Middle East, Europe, NSC Americas, Australia Transmission 1. EEE Transmitted by mosquitoes; not horse-horse or horse- human; dead-end hosts Life cycle of alphaviruses between birds/rodents and mosquitoes Sylvatic cycle between passerine birds and Culiseta melanura 2. MADV principal vector belong to Culex (Melanoconion) spp 3. WEE transmitted by C. tarsalis, Dermacentor andersoni 4. VEE in jungle or swampy areas; two life cycles, the enzootic and epizootic cycle a. Enzootic – mosquito (subgenus Melanoconion/C. cedecci) serves as primary vector for bird/rodent- mosquito life cycle; sylvatic rodents spiny and cotton rats b. Epizootic – mutation to subtype I (A, B, C and possibly E) with change in mammalian pathogenesis b. and several bridge vectors; horse infection becomes predominant feature in maintenance of epizootic VEE All encephalitides caused by Flaviviruses transmitted by mosquito, Culex spp usually the most efficient 5. WNV – widest geographic distribution of all flaviviruses  Equine Encephalomyelitis Clinical Signs: Neurologic signs occur 9-11 days after infection 1. Quiet and depressed 2. Ataxia, wandering, impaired vision, reduced reflexes, circling, inability to swallow, drooling, fever 3. Paralysis usually followed by death 2-3 days after onset of signs Eastern Equine Encephalitis (EEE) Venezuelan Equine Encephalitis (VEE) “Paddling”  Equine Encephalomyelitis Diagnosis: 1. Clinical assessment 2. CSF examination – in EEE with neutrophilic pleocytosis (count > 50%) 3. IgM capture ELISA – 85-90%; neutralizing antibodies gold standard (IgG) 4. PCR – midbrain and brain stem Treatment: 1. Supportive nursing care 2. Management of pain and inflammation  3. For WNV, flunixin meglumine 1.1mg/kg, IV, bid to prevent muscle tremors and fasciculations Prevention 1. Core annual vaccination one month prior to mosquito season; formalin-inactivated whole viral vaccines Mares vaccinated 1 month before foaling With colostrum, foals vaccinated at 5-6 months plus 2 additional vaccinations 30 and 90 days after Zoonotic risks  Equine Influenza Highly contagious respiratory disease caused by Orthomyxovirus Influenza virus A/equine 2 Subtyupes H7N7 and H3N8; H3N8 spreads rapidly and cause severe clinical diases Horses 1-5 years most susceptible Endemic in many countries except New Zealand and Iceland Rarely fatal except in donkeys, zebras and debilitated horses Transmission Incubation period < 48 hrs Morbidity 60-90% Mortality