Equine Herpesvirus Exam 2 Flashcards
Equine herpesvirus is also called
equine rhinopneumonitis
What types of EHV infect horses?
1-5
What are the two most common types of EHV?
1 and 4
What demographic of horse is EHV primarily seen in?
young horses
What % of horses are exposed to the virus by what age?
80-90% are exposed by 2 years old
How is EHV spread?
-direct horse to horse contact (through respiratory system)
-indirect (fomites, personnel)
What types of EHV infect wild horses and zebras?
EHV 6-9
What is the key feature that distinguishes EHV-1 and 4 from each other?
-EHV-1 infects a variety of cell types (respiratory epithelial cells, neuronal cells, lymphoid cells, and endothelial cells)
-EHV-4 infects the epithelial cells of the respiratory system only
What is the prognosis of EHV-4
favorable
What can EHV-1 cause?
abortion, neurological disorders, neonatal death, ocular disease, and death
EHV-1 and 4 are enveloped viruses which means:
they are highly susceptible to destruction by common disinfectants (like soaps)
Herpes virus in humans
goes latent, and reappears during high stress or being in the sun for too long
Main reservoir of EHV
latently infected horse (keeps the virus alive)
How long does EHV live in the environment?
average of 7 days
How can EHV be disactivated?
easily by heat and disinfectants
One stud farms, how do foals acquire the virus?
from adult mares that shed the virus asymptomatically
What age do outbreaks normally occur in horses?
between weaning to 2-3 years old
Risk factors for outbreaks:
-overcrowding
-heavy parasite burden
-poor nutritional state
-climatic extremes
-concurrent disease
-intermingling of animals from different social groups
Morbidity of EHV
can reach 100%, it is very contagious
A large majority of recovered horses carry what for life?
latent EHV infections
The latency of EHV comes from:
T lymphocytes and neurons of the trigeminal ganglia
When does reactivation of latency infected horses occur?
-after transport
-rehousing
-weaning
-inclement weather
-surgery
-corticosteroids administration
During reactivation, do symptoms occur?
no (silent virus shedding)
Can closed populations of horses still get EHV?
yes, because the horses can carry it without being detected for a long time
What can reactivation of EHV-1 specifically cause?
abortion, due to the destruction of blood vessels or endothelial cells in uterus
Where does EHV replicate?
in the upper respiratory tract
What types of cells does EHV-1 infect?
endothelial cells, lymphocytes, and monocytes
Is EHV-1 or 4 more aggressive?
1
Why is EHV-1 more aggressive?
-it affects more cells
-viremia (virus in bloodstream) occurs causing wide dissemination of virus including to the uterus and CNS
-reaches trigeminal neurons 48 hrs after infection and establishes latency
Why is EHV-4 less aggressive?
-have low affinity for endothelial cells
-don’t establish viremia, so don’t cause abortion or neurologic disease
What does EHV-1 cause in the uterus and CNS?
vasculitis and ischemia
When does EHV caused abortion usually occur during pregnancy?
late term abortion
What can EHV predispose horses for?
bacterial infections that lead to bacterial pneumonia
When should foals begin to get vaccinated?
4-6 months old
Symptoms of EHV-4 in young animals:
-more serious disease
-depression
-anorexia
-biphasic fever (days 1-2 and 6-7)
-nasal discharge
-ocular discharge
Symptoms of EHV-4 in older animals or animals previously exposed:
very mild respiratory disease or no sign of disease
EHV-1 is uncommon to cause clinically apparent respiratory disease except in:
very young foals infected with highly virulent strain
(mares abort but without previous signs of respiratory disease)
How long is the incubation period?
up to 10 days
What respiratory disease symptom is not common with EHV?
coughing, unless horse is kept in unclean environment or is not rested from training
How is EHV diagnosed?
in the lab with virus isolation, CSF, and serology (with horses showing clinical signs)
-very difficult to detect latently infected horses
How is EHV treated?
-NSAIDs for fever, maybe antibiotics or fluids
-generic treatments
Do mares who abort from EHV have trouble getting pregnant again or further complications?
no
How many commercially available vaccines are there?
8
What do vaccines do for EHV?
they don’t prevent respiratory disease but they usually diminishes shedding
Effectiveness of the vaccines:
-reduces abortion in mares by 75%
There are vaccinations available for what types of EHV?
1 and 4
Equine Herpes Myeloencephalytis (EHM)
a genetic variant of EHV-1 that is more commonly associated with neurologic disease (both EHV-1 viruses can cause neurologic disease though)
Is there a vaccine for EHM?
no
Is EHM treated differently than EHV-1?
no, but identifying which virus it is could be grounds for more concern about development of neurological disease
What can vaccines help with EHM?
limits nasal shedding of EHV-1 and dissemination of infection which in turn limits the spread of EHM
What types of horses is viral shedding reduced in?
horses with high circulating titers of virus-neutralizing antibodies
What vaccines have the best ability to limit nasal shedding?
-the 2 high-antigen load, inactivated vaccines that are licensed for control of abortion (Pneumabort-K: Pfizer and Prodigy Merck)
-a MLV vaccine (Rhinomune and Boehringer Ingelheim Vetmedica)
-an inactivated vaccine (Calvenza and Boehringer Ingelheim Vetmedica)
How do you manage EHV prevention?
-vaccinate pregnant mares and show horses
-no stress environments
-don’t mix age groups
-cleanliness
-quarantine new horses
-isolate sick horses
-don’t mix new horses with pregnant mares in the last 1/3 of the pregnancy
-don’t mix resident group with itinerant group
-don’t disrupt established groups (causes stress)
