Dr. Tee (Thera) Fox, Veterinarian, Markdale Veterinary Services
Mosquito-borne virus infections of horses pose a continuous and expanding threat to equine health in Canada and internationally. The majority of equine mosquito-borne diseases in Canada today are preventable by immunization. What do we need to know to keep our Horses safe from these debilitating diseases? Topics covered will include: West Nile Virus (WNV), Eastern Equine Encephalitis (EEE), and Western Equine Encephalitis (WEE).
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Protect Your Horse from Mosquito-Borne Diseases
1. Grey Bruce Farmer’s Week 2014
The Changing
Face of MosquitoBorne Diseases
Protect Your Horse Against Infectious
Diseases
Dr. Tee (Thera) Fox, DVM
2. Horse Health Education: Mosquito-Borne Diseases
What are Mosquito-Borne Diseases?
• Mosquitoes are important
vectors (agents) in the
transmission of animal diseases.
• Mosquito-borne diseases
involve the transmission of
disease from animal-toanimal, animal-to-person, or
person-to-person, by
mosquitoes without causing any
symptoms of disease in the
mosquito itself.
3. Horse Health Education: Mosquito-Borne Diseases
Why are Mosquito-Borne Diseases Important?
• Mosquitoes cause more human
suffering than any other organism -over one million people worldwide die
from mosquito-borne diseases every
year.
• Not only can mosquitoes carry diseases
that afflict humans, they also transmit
diseases and parasites that our horses
and other pets are very susceptible to.
4. Horse Health Education: Mosquito-Borne Diseases
Why are Mosquito-Borne Diseases Important?
While only a small number of
mosquito-borne pathogens are
currently important to public
health in Canada, there is risk of
emergence of new diseases
given the increasing pace of
global trade and travel, ongoing
climate and environmental
changes, and gaps in surveillance
and control.
5. Horse Health Education: Mosquito-Borne Diseases
Why are Mosquito-Borne Diseases Important?
The major mosquito-borne
disease of public health
importance in Ontario is West
Nile Virus (WNV) with
surveillance attention also being
focused on Eastern Equine
Encephalitis Virus (EEEV) that is
currently emerging in parts of
Northern US and Canada which
poses a concern for both human
and animal health.
6. Horse Health Education: Mosquito-Borne Diseases
Why are Mosquito-Borne Diseases Important?
Both the Eastern Equine
Encephalitis Virus and West
Nile, The virus can cause severe
neurological disease due to
inflammation of the brain
(encephalitis) and spinal cord
(myelitis) in humans and horses.
7. Horse Health Education: Mosquito-Borne Diseases
Transmission:
In each of these diseases the viral
material is cycled between birds (and
in some cases small rodents) and
mosquitoes, the viral material is then
amplified (concentrated) in the birds
and transmitted to mammals
(including horses) and humans through
the bite of an infected mosquito.
9. Horse Health Education: Mosquito-Borne Diseases
Transmission:
Horses and humans are
dead-end hosts for EEEV
and WNV, meaning a
horse or human cannot
pass the diseases on to
others.
10. Horse Health Education: Mosquito-Borne Diseases
Transmission :
Most cases occur during the height of vector (mosquito)
season. In this area this is between June and
November, however in warmer climates cases may be
seen at any time of year.
The conditions that favor outbreaks vary from year to
year; hence the incidence also varies from year to year.
Some locations may go for several years with few or no
cases reported, and then have a year with large
numbers of cases.
11. Horse Health Education: Mosquito-Borne Diseases
Infection:
Symptoms usually occur from 3 to 12
days after the bite of an infected
mosquito.
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12. Horse Health Education: Mosquito-Borne Diseases
Infection:
Symptoms may include:
• Fever
• Depression
• Anorexia
(loss of appetite)
• Muscle Twitching/Tremors
• Hypersensitivity of the skin
• Dementia
• Circling
•
•
•
•
•
•
•
Head Pressing
Ataxia (loss of coordination)
Blindness
Inability to swallow
Paralysis (Inability to move)
Recumbency
(inability to stand)
Convulsions
13. Horse Health Education: Mosquito-Borne Diseases
Infection:
Clinical signs of EEEV and
WNV (such as circling, headpressing and convulsions) can
mimic a variety of diseases with
neurological symptoms
including: Rabies, Botulism, Hep
atic Encephalopathy, Equine
Protozoal
Myeloencephalitis, Tetanus, Equ
ine Herpes Virus 1, and Lead
Poisoning.
14. Horse Health Education: Mosquito-Borne Diseases
Treatment:
At present time, there is no specific
anti-viral treatment for WNV or
EEEV. Management should focus
on controlling pain and
inflammation.
Anti-inflammatory drugs should be
provided as soon as possible to
control inflammatory changes in
the central nervous system.
15. Horse Health Education: Mosquito-Borne Diseases
Treatment:
Other supportive measures
such as intravenous
fluids, sedatives, and
nutritional support can be
important components of
therapy.
16. Horse Health Education: Mosquito-Borne Diseases
Treatment:
Horses infected with EEEV
often do not survive.
Mortality rates can be as high
as 90%.
Those that do survive often
have long term neurological
deficits.
17. Horse Health Education: Mosquito-Borne Diseases
Treatment:
The mortality rate for WNV is 25 to
35 percent.
Those that survive may recover
completely or they may suffer from
residual neurological signs long
term.
18. Horse Health Education: Mosquito-Borne Diseases
Prevention and Control:
Consider vaccinating your horse against these diseases.
The AAEP Infectious Disease committee has identified “Core
Vaccines”. These core vaccines have clearly demonstrated
efficacy and safety.
The following equine vaccines meet these criteria and are
identified as ‘core’ in these guidelines:
•
•
•
•
Tetanus
Rabies
Eastern and Western Equine Encephalitis
West Nile Virus
19. Horse Health Education: Mosquito-Borne Diseases
Prevention and Control:
It is recommended that all
horses receive a vaccination
against “core” diseases at least
annually. Pregnant mares and
foals may require additional
vaccinations.
Please consult your veterinarian to determine what vaccines are right for you.
20. Horse Health Education: Mosquito-Borne Diseases
Prevention and Control:
The best time to vaccinate is
during the spring 1-2 months
before mosquitoes become
active.
In areas or locations with more
persistent mosquito populations
some veterinarians choose to
add a booster shot in the fall to
ensure extra protection yearround.
21. Horse Health Education: Mosquito-Borne Diseases
Prevention and Control:
Eliminate potential mosquito
breeding sites. Dispose of old
receptacles, tires and
containers and eliminate
areas of standing water.
22. Horse Health Education: Mosquito-Borne Diseases
Prevention and Control:
Thoroughly clean livestock watering
troughs at least weekly.
Use larvicides to control mosquito
populations when it is not possible to
eliminate particular breeding sites.
• Such action should only be taken,
however, in consultation with your
local mosquito control authority.
23. Horse Health Education: Mosquito-Borne Diseases
Prevention and Control:
Keep your horse indoors during
the peak mosquito activity
periods of dusk to dawn.
Screen stalls if possible or at least
install fans over your horse to help
deter mosquitoes.
24. Horse Health Education: Mosquito-Borne Diseases
Prevention and Control:
Avoid turning on lights inside the
stable during the evening or overnight
as they attract mosquitoes.
Use insect repellants on your horse
that are designed to repel mosquitoes
can help reduce the chance of being
bitten.
25. Horse Health Education: Mosquito-Borne Diseases
Prevention and Control:
Remove any birds, including
chickens, located in or close to a
stable.
Don’t forget to protect yourself as
well. When outdoors in the
evening, wear clothing that
covers your skin and apply plenty
of mosquito repellent.
26. Horse Health Education: Mosquito-Borne Diseases
Prevention and Control:
Public Health Ontario currently
has an adult mosquito-based
surveillance program focused on
identifying mosquito pools that
are positive for those species of
mosquitos that are capable of
transmitting WNV and EEEV.
When those species are identified
they are then tested to determine
if they are positive for the disease
and identify areas of concern.
27. Horse Health Education: Mosquito-Borne Diseases
Equine Neurological Disease Surveillance 2011:
In 2011, Ontario
had four equine
EEE cases, with a
probable but
unconfirmed fifth
case, as well as
eight equine cases
of WNV.
28. Horse Health Education: Mosquito-Borne Diseases
Equine Neurological Disease Surveillance 2012:
In 2012, Ontario
had six equine
WNV cases, and
one equine rabies
case.
29. Horse Health Education: Mosquito-Borne Diseases
Equine Neurological Disease Surveillance 2013:
In 2013, Ontario
had eleven equine
WNV cases, and
one EEE case.
31. Horse Health Education: Mosquito-Borne Diseases
IN A NUTSHELL:
Good husbandry management practices, mosquito population
control and appropriate vaccination protocols are the best and
most cost- effective weapon you have against mosquito-borne
diseases of the horse.
32. Horse Health Education: Mosquito-Borne Diseases
QUESTIONS:
IF YOU THINK YOU’RE
TOO SMALL TO MAKE A
DIFFERENCE YOU
HAVEN’T SPENT A NIGHT
WITH A MOSQUITO.
-AFRICAN PROVERB