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7 Cards in this Set

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Equine herpesviruses: Etiology
1) Herpetoviridae
2) Alphaherpesvininae
3) EHV-1
4) EHV-2: Equine cytomegalovirus
5) EHV-3: Self-limiting venereal infection in mares and stallions
6) EHV-4
7) EHV-5: Related to EHV-2
8) EHV-6: Donkeys
9) EHV-7: Donkeys-- related to EHV-2 and EHV-5
10) EHV-8: Donkeys-- related to EHV-1; rhinitis induced experimentally
11) EHV-9: zebras and polar bears
Clinical syndromes: Rhinopneumonitis
1) Both EHV-1 and EHV-4 can induce rhinopneumonitis
2) Primarily seen in weanling horses (first year of life)
3) Also seen following exposure to large groups of horses (racing, training)
4) Incubation time is 3-4 days
5) Signs: fever, inappetance, lethargy, (hind limb edema), submandibular and retropharyngeal LN enlargement, nasal discharge (serous--> mucopurulent)
6) lesions seen in mucous membranes in upper respiratory tract and sometimes lungs
7) prone to secondary bac infx
8) Leads to performance deficits during and after clinical signs
9) infx in older horses mostly subclinical
10) EHV-1 and 4 induce only mild dz
Clinical syndromes: Abortion and perinatal disease
1) Abortions occur weeks to months after infection
2) most abortions occur 9-11 mos into gestation
3) rarely seen before 4 mos gestation
4) does not lead to other complications for mare
5) fetus usually delivered dead
6) perinatal foal mortalities may be seen when group of aborting mares is close to term
7) primary abortion leads to rapid spread of virus--> subsequent abortions
8) virus cleared rapidly after abortion--> no effect on future pregnancy
9) Isolate aborting mare-- fetus and placenta are virus-laden
10) subsequent abortions usually rare
11) If you infect sero+ mares--> abortion. Fetuses are virus-free-- aborted due to vasculitis w/ antigen-Ab complex formation leading to ischemic damage to endometrium
Clinical syndromes: Myeloencephalitis
1) seen most often in pregnant or recently foaled mares
2) Associated w/ some EHV-1 (after polymerase mutation)
3) Incubation is 4-7 days
4) fever and serous nasal discharge first signs
5) next is acute onset ataxia and weakness of trunk and hind limbs. Progress rapidly for 48hrs, then stabilize
6) urinary retention/incontinence, bladder distention, tail weakness, fecal retention, erectile problems, sensory deficits
7) cranial nerve involvement is uncommon (affects back end of horse)
EHV: pathogenesis
1) Exposure to virus aerosol
2) incubation: 4-7 days
3) virus replication in mucosal epi cells of nasal passages, pharynx, tonsils
4) vesicular lesions
5) Cell-associated viremia and invasion of sensory nerve endings of cranial nerves
6) clincial syndrome, then lifelong latency in nervous and maybe lymphoid tissue
7) Reactivation of latency--> virus shedding from nose
8) can lead to abortion in pregnant mares in close contact w/ reactivated horse
EHV: Diagnosis
1) Ante mortem: a) clinical signs, b) VI from nasal swabs or whole blood, c) PCR, d) testing of paired sera for VN Ab
2) Post mortem: a) histologic lesions, b) FA, c) IHC
EHV: Prevention
1) MLV w/ EHV-1
2) inactivated vacc containing EHV-1 and EHV-4
3) CMI better than humoral
4) protection against reinfection is 2-3 mos
5) inactivated vaccs during pregnancy
6) Consecutive doses at 5-7 and 9 mos gestation
7) Efficacy of EHV-1 vacc against neuro form has not been demonstrated