the changing face of mosquito-borne diseases

The Changing Face of Mosquito-Borne Diseases

Dr. Tee (Thera) Fox, DVM

Grey Bruce Farmer’s Week 2014

Protect Your Horse Against Infectious Diseases

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-to-animal, animal-to-person, or person-to-person, by mosquitoes without causing any symptoms of disease in the mosquito itself.


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.


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.


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.


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.


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.

Disease Transmission Cycle:



Transmission:Horses and humans are dead-end hosts for EEEV and WNV, meaning a horse or human cannot pass the diseases on to others.

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.



Infection:Symptoms usually occur from 3 to 12 days after the bite of an infected mosquito.

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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


Infection:Clinical signs of EEEV and WNV (such as circling, head-pressing and convulsions) can mimic a variety of diseases with neurological symptoms including: Rabies, Botulism, Hepatic Encephalopathy, Equine Protozoal Myeloencephalitis, Tetanus, Equine Herpes Virus 1, and Lead Poisoning.

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.


Treatment:

Other supportive measures such as intravenous fluids, sedatives, and nutritional support can be important components of therapy.


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.


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.



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

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.


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 year-round.



Eliminate potential mosquito breeding sites. Dispose of old receptacles, tires andcontainers and eliminate areas of standing water.



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.



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.



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.



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.



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.


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.



In 2012, Ontario had six equine WNV cases, and one equine rabies case.



In 2013, Ontario had eleven equine WNV cases, and one EEE case.


Cases Of Equine Neurological Disease in Ontario

2008 2009 2010 2011 2012 20130

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12

EEEWNVRabies

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.


QUESTIONS:


IF YOU THINK YOU’RE TOO SMALL TO MAKE A DIFFERENCE YOU HAVEN’T SPENT A NIGHT WITH A MOSQUITO. -AFRICAN PROVERB