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What are the clinical signs of West Nile virus infection for horses?

posted by Horse Owner Today    |   August 19, 2011 07:48

Animals (particularly horses) infected with the virus show neurological disturbances. Clinical signs may include:

  • ataxia (lack of coordination);
  • depression or lethargy;
  • fever;
  • head pressing or tilt;
  • impaired vision;
  • inability to swallow;
  • loss of appetite;
  • muscle weakness or twitching;
  • partial paralysis;
  • coma; and
  • death.

The clinical signs of WNV in mammals can be confused with rabies.

Most infected domestic birds do not show signs of infection, and only domestic geese appear to be particularly susceptible to disease and/or death when infected.

WNV-infected geese will show signs of depression, loss of appetite, inability to stand, weight loss and death. The virus can be difficult to distinguish from Newcastle Disease and Avian Influenza in domestic birds.




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General | disease

Response to Central Nervous System Signs in Horses in West Nile Virus Endemic Areas

posted by Horse Owner Today    |   August 19, 2011 07:36


With numerous cases of the West Nile Virus (WNV) reported in horses in several Canadian provinces in the last couple of years, the question has arisen as to how to deal with situations where horses with central nervous system (CNS) neurological signs are reported from the field or at registered slaughter establishments. Clinical signs of WNV in horses could be indistinguishable from those seen in rabies. Thus, any horses showing neurological signs suggestive of and clinically indistinguishable from rabies have to be reported to the Canadian Food Inspection Agency (CFIA) for investigation.

The following provides a brief description of the epidemiology and pathogenesis of WNV in horses and, based on this, the course of action the CFIA will take to fulfill its mandate of protecting human and animal health.

Epidemiology and Pathogenesis of West Nile Virus in Horses

Natural WNV infections in horses have been reported in Europe, Africa, the Middle East and recently in North and South America. It appears that WNV affects horses of all ages, breeds and sexes. Its occurrence in North America is seasonal, and coincides with the presence of the mosquito vector. Most cases of WNV in horses are reported from mid-August to late October. It is estimated that between 10 to 40% of horses in endemic areas can be infected with WNV, but only 8% of these will manifest clinical signs of the disease. The WNV incubation period is usually from 5 to 15 days with a low level of transient viremia < 102.5 plaque-forming unit per milliliter (PFU/ml) of serum (range 101.0 to 103.0) developing one to two days post infection. Four to eight days following the infection, the WNV is no longer detectable in the blood of infected horses. Neurological signs may become apparent from 5 to 22 days post infection and most horses are usually not viremic at that stage. The clinical signs of WNV in order of their frequency include: ataxia, weakness of limbs, recumbency, muscle fasciculation, fever, paralyzed or drooping lip, twitching face or muzzle, teeth grinding, blindness, and traumatic lesions of the forelimbs and head due to compulsive movement. WNV in horses does not result in any gross pathological lesions and the virus can only be isolated from the brain and spinal cord of clinically ill horses. Approximately 60 to 70% of horses with clinical signs may fully recover.

Considering the sporadic occurrence of WNV-associated diseases in horses, the development of low-magnitude and short-duration viremia, as well as limited amount of antigen detected in CNS tissue, horses are considered an incidental and dead-end host of WNV. Consequently, horses do not play a significant role in the epidemiology of WNV and do not pose a risk to humans. Slaughter of clinically healthy horses under normal circumstances does not constitute any WNV health hazard to inspection staff or plant employees.



Human West Niles Cases in Canada & USA as of August 17, 2011

posted by Horse Owner Today    |   August 19, 2011 07:24

Total USA cases 53 as of August 17, 2011

Total Canada cases 1 as of August 17, 2011


State Cases
Arizona 4
California 10
Colorado 1
Florida 8
Georgia 1
Louisiana 2
Mississippi 14
Nebraska 1
New Jersey 1
North Dakota 2
South Dakota 1
Texas 6
Virgina 1
Wyoming 1


West Nile Dead Bird Surveillance 2011

posted by Horse Owner Today    |   August 19, 2011 07:20

2011 Summary by Province (Dead Bird Surveillance Map 2011) www.ccwhc.ca

Region Received Tested Positive Negative Pending
British Columbia 5 5 0 5 0
Alberta 0 0 0 0 0
Saskatchewan 1 1 0 1 0
Manitoba 1 1 0 1 0
Ontario 64 64 2 39 23
Quebec 1 1 0 1 0
New Brunswick 1 1 0 1 0
Nova Scotia 0 0 0 0 0
Prince Edward Island 0 0 0 0 0
Newfoundland and Labrador 0 0 0 0 0
Yukon Territory 0 0 0 0 0
Northwest Territories 0 0 0 0 0
Nunavut 0 0 0 0 0
TOTAL 73 73 2 48 23


FAQ's on Mosquitoes

posted by Horse Owner Today    |   August 5, 2011 08:26

Many websites provide information on mosquitoes, their habitats, behaviors, and impact on humans. We hope you can find answers to your questions on this page or website or through our links page.


How many kinds of mosquitoes are there? About 3000 species of mosquitoes have been described on a world-wide basis. Approximately 150 are known to occur in North America. The term "Mosquito State" is appropriate for New Jersey because 63 species of mosquitoes have been found within its boundaries, to date. Scientists group species by genus on the basis of the physical characteristics they share. The 3000 mosquito species found in the world are divided among 28 different genera. The genus Aedes contains some of the worst pests. Many members of the genus Anopheles have the ability to transmit human malaria. Ten different genera occur in New Jersey including: Aedes, Anopheles, Culex, Culiseta, Coquillettidia, Psorophora, Orthopodomyia, Uranotaenia, Toxorhynchites and Wyeomyia. It is sometimes more convenient to group mosquitoes by the breeding habitat they use. The major habitat groups found in New Jersey include: "Snowpool Mosquitoes", "Floodwater Mosquitoes", "Swamp Breeding Mosquitoes" and "Container Breeding Mosquitoes".

Why do mosquitoes bite? Mosquitoes belong to a group of insects that requires blood to develop fertile eggs. Males do not lay eggs, thus, male mosquitoes do not bite. The females are the egg producers and "host-seek" for a blood meal. Female mosquitoes lay multiple batches of eggs and require a blood meal for every batch they lay. Few people realize that mosquitoes rely on sugar as their main source of energy. Both male and female mosquitoes feed on plant nectar, fruit juices and liquids that ooze from plants. The sugar is burned as fuel for flight and is replenished on a daily basis. Blood is reserved for egg production and is imbibed less frequently. (See the video)

Why do mosquitoes leave welts when they bite? When a female mosquito pierces the skin with her mouthparts, she injects a small amount of saliva into the wound before drawing blood. The saliva makes penetration easier and prevents the blood from clotting in the narrow channel of her food canal. The welts that appear after the mosquito leaves is not a reaction to the wound but an allergic reaction to the saliva injected to prevent clotting. In most cases, the itching sensation and swellings subside within several hours. Some people are highly sensitive and symptoms persist for several days. Scratching the bites can result in infection if bacteria from the fingernails are introduced to the wounds.

Why are some people more attractive to mosquitoes than others? Scientists are still investigating the complexities involved with mosquito host acceptance and rejection. Some people are highly attractive to mosquitoes and others are rarely bothered. Mosquitoes have specific requirements to satisfy and process many different factors before they feed. Many of the mosquito's physiological demands are poorly understood and many of the processes they use to evaluate potential blood meal hosts remain a mystery. Female mosquitoes use the CO2 we exhale as their primary cue to our location. A host seeking mosquito is guided to our skin by following the slip stream of CO2 that exudes from our breath. Once they have landed, they rely on a number of short range attractants to determine if we are an acceptable blood meal host. Folic acid is one chemical that appears to be particularly important. Fragrances from hair sprays, perfumes, deodorants and soap can cover these chemical cues. They can also function to either enhance or repel the host seeking drive. Dark colors capture heat and make most people more attractive to mosquitoes. Light colors refract heat and are generally less attractive. Detergents, fabric softeners, perfumes and body odor can counteract the effects of color. In most cases, only the mosquito knows why one person is more attractive than another.

How long do mosquitoes live? Mosquitoes are relatively fragile insects with an adult life span that lasts about 2 weeks. The vast majority meet a violent end by serving as food for birds, dragonflies and spiders or are killed by the effects of wind, rain or drought. The mosquito species that only have a single generation each year are longer lived and may persist in small numbers for as long as 2-3 months if environmental conditions are favorable. Mosquitoes that hibernate in the adult stage live for 6-8 months but spend most of that time in a state of torpor. Some of the mosquito species found in arctic regions enter hibernation twice and take more than a year to complete their life cycle.

Where do mosquitoes go in the winter? Mosquitoes, like most insects, are cold blooded creatures. As a result, they are incapable of regulating body heat and their temperature is essentially the same as their surroundings. Mosquitoes function best at 80o F, become lethargic at 60o F and cannot function below 50o F. In tropical areas, mosquitoes are active year round. In temperate climates, adult mosquitoes become inactive with the onset of cool weather and enter hibernation to live through the winter. Some kinds of mosquitoes have winter hardy eggs and hibernate as embryos in eggs laid by the last generation of females in late summer. The eggs are usually submerged under ice and hatch in spring when water temperatures rise. Other kinds of mosquitoes overwinter as adult females that mate in the fall, enter hibernation in animal burrows, hollow logs or basements and pass the winter in a state of torpor. In spring, the females emerge from hibernation, blood feed and lay the eggs that produce the next generation of adults. A limited number of mosquitoes overwinter in the larval stage, often buried in the mud of freshwater swamps. When temperatures rise in spring, these mosquitoes begin feeding, complete their immature growth and eventually emerge as adults to continue their kind.

Can mosquitoes carry diseases? Any insect that feeds on blood has the potential of transmitting disease organisms from human to human. Mosquitoes are highly developed blood-sucking insects and are the most formidable transmitters of disease in the animal kingdom. Mosquito-borne diseases are caused by human parasites that have a stage in their life cycle that enters the blood stream. The female mosquito picks up the blood stage of the parasite when she imbibes blood to develop her eggs. The parasites generally use the mosquito to complete a portion of their own life cycle and either multiply, change in form inside the mosquito or do both. After the mosquito lays her eggs, she seeks a second blood meal and transmits the fully developed parasites to the next unwitting host. Malaria is a parasitic protozoan that infects the blood cells of humans and is transmitted from one human to the next by Anopheles mosquitoes. Encephalitis is a virus of the central nervous system that is passed from infected birds to humans by mosquitoes that accept birds as blood meal hosts in addition to humans. Yellow fever is a virus infection of monkeys that can either be transmitted from monkey to human or from human to human in tropical areas of the world. Dog heartworm is a large filarial worm that lives in the heart of dogs but produces a blood stage small enough to develop in a mosquito. The dog heartworm parasite does not develop properly in humans and is not regarded as a human health problem. A closely related parasite, however, produces human elephantiasis in some tropical areas of the world, a debilitating mosquito-borne affliction that results in grossly swollen arms legs and genitals.

Can mosquitoes transmit AIDS? The HIV virus that produces AIDS in humans does not develop in mosquitoes. If HIV infected blood is taken up by a mosquito the virus is treated like food and digested along with the blood meal. If the mosquito takes a partial blood meal from an HIV positive person and resumes feeding on a non-infected individual, insufficient particles are transferred to initiate a new infection. If a fully engorged mosquito with HIV positive blood is squashed on the skin, there would be insufficient transfer of virus to produce infection. The virus diseases that use insects as agents of transfer produce tremendously high levels of parasites in the blood. The levels of HIV that circulate in human blood are so low that HIV antibody is used as the primary diagnosis for infection.



Get The Buzz on Bugs

posted by Horse Owner Today    |   August 5, 2011 08:16


Minimize exposure to mosquitoes by reducing the potential breeding areas.  A mosquito takes 4 (four) days to develop from an egg into a flying, biting adult mosquito. 

Some suggestions include:

Drain small, warm still puddles of water including poorly drained eavestroughs, birdbaths, used tires, pool covers, toys or any standing water.

Clean water troughs on a weekly basis.

Cover rain barrel openings with screening.

Avoid outdoor activities during peak times of mosquito feeding - dawn and dusk.

Consider offering screened housing.


  Topical insect repellents and smudging can be useful.


  Keeps grass short around yardsite.


Eastern Equine Encephalitis (EEE) & Horses

posted by Horse Owner Today    |   August 5, 2011 08:00

Questions Regarding Eastern Equine Encephalitis and Horses

by Wayne J. Crans, Associate Research Professor in Entomology

Rutgers Cooperative Extension Fact Sheet # FS737


Eastern equine encephalitis, commonly referred to as EEE, is a virus disease of wild birds that is transmitted to horses and humans by mosquitoes. The virus is found near wetland habitats along the eastern seaboard from New England to Florida. New Jersey represents a major focus for the infection with some form of documented viral activity nearly every year. Horse cases are most common in the southern half of New Jersey because the acid water swamps that produce the major mosquito vectors are especially prevalent on the southern coastal plain.

The virus responsible for EEE attacks the central nervous system of its host and horses are particularly susceptible to the infection. Onset is abrupt and horse cases are almost always fatal. Symptoms include unsteadiness, erratic behavior and a marked loss of coordination. There is no effective treatment and seizures resulting in death usually occur within 48-72 hours of an animal's first indications of illness.


EEE is not new to New Jersey, but the disease is poorly understood by the average horse owner. A vaccine is available, but a surprisingly high number of valuable animals go unvaccinated each year. This fact sheet has been designed to answer the most commonly asked questions regarding EEE and its potential impact on New Jersey's horse industry. For additional information on the subject, contact your County Agricultural Agent, your County Mosquito Control Agency, the New Jersey Agricultural Experiment Station and the New Jersey Department of Agriculture - Division of Animal Health.

Where Does EEE Come From?

EEE virus occurs naturally in a wide variety of wild song birds. Blood samples from New Jersey birds indicate that Blue Jay, Wood Thrush, Tufted Titmouse, Chickadee, Catbird and Cardinal show the highest incidence of infection in our state. EEE virus normally appears in local bird populations shortly after the nesting season is over in the spring. Mosquitoes transmit the infection from bird to bird during the early summer months and infections usually peak sometime in August. In some years, the virus remains in local bird populations and does not pose a health threat to horses or humans. When mosquito populations are high, however, transfer from birds to horses and/or humans is possible. In a typical outbreak year, horse cases begin to appear in unvaccinated animals in mid-summer. All equine cases are the result of mosquitoes which have fed on infected birds and then feed on unvaccinated horses.

Does EEE Represent a Serious Health Threat to Humans?

Human cases of EEE are very rare, averaging less than 1 overt case every 5 years. The disease, however, produces serious illness when it is contracted via mosquito bite and the probability of recovery is less than 50%. In overt cases, the virus produces an illness that begins with low fever, headache and stiff neck. As the disease progresses, the patient can fall into coma with death as a likely outcome. Recovery is possible but individuals that do recover usually do so with brain damage. Children appear to be more susceptible to overt cases than adults. Research indicates that most humans that are bitten by infected mosquitoes abort the infection in the early stages and recover with no evidence that they ever had the disease. The overt to inapparent ratio of encephalitis in New Jersey is estimated at I overt case for every 23 individuals that are bitten by infected mosquitoes. Salt marsh mosquitoes are the main transmitters of EEE to humans in New Jersey, thus human encephalitis is a coastal phenomenon that is associated with the large populations of mosquitoes encountered at the shore. To date, no human involvement has ever been associated with the horse cases that are relatively common on the coastal plain in the southern portion of the state.

Can Humans Contract EEE Directly from Horses?

The virus that causes EEE cannot be passed from horses to humans by contact, body fluids or any other physical mechanism. Moreover, horses do not circulate sufficient virus in the blood stream to reinfect mosquitoes. EEE is only acquired from mosquitoes that have previously fed on infected birds. A sick horse does not pose a health threat to its human owners. A sick horse is an indication that the local bird population is circulating virus and that local mosquitoes are making contact with the infection. Transmission is not possible from horse to horse, horse to human or even horse to mosquito. Virtually the only way that EEE can be acquired is via the bite of a mosquito that has fed upon an infected bird.

What is the Best Method of Protecting My Horse?

The virus that produces EEE in horses is widespread in wild bird populations and professional vaccination is the only method available to protect horses from the disease. Vaccinations should be administered by a licensed veterinarian to assure that viable vaccine is utilized and injections are properly administered. Mistakes in vaccination protocol by well-meaning horse owners can result in ineffective protection in an animal that was thought to be risk free. All too frequently, owner vaccinated horses develop overt cases indicating that the animal was improperly vaccinated or was vaccinated with vaccine that had lost its protective properties. Properly administered vaccinations are effective for only one year, thus, booster shots are required on an annual basis. Newly vaccinated animals require a two-shot series administered 2-4 weeks apart before protection can be guaranteed. Foals should be re-vaccinated during summer to ensure protection during the first year of life. It is recommended in the face of a fall epidemic, horses vaccinated in March should be boostered later in the season.

What is the Best Method of Protecting My Family If My Horse Contracts EEE?

Although human cases have never been associated with equine EEE, a sick horse is an indication that the virus is present in local mosquitoes. There is no human vaccine available for routine usage, thus mosquito avoidance is the best protection in an area where EEE is known to be present. Homeowners should contact their county mosquito control agency and make them aware of the situation. Mosquito control personnel are familiar with the EEE cycle and have the expertise to reduce the mosquitoes that function in the cycle. Have your family and employees avoid mosquito-infested areas and use insect repellents when exposure is unavoidable. Eliminating water-holding containers from your property (buckets, tires and other receptacles) will reduce mosquito breeding in the immediate vicinity. Horse troughs provide excellent mosquito breeding habitat and should be flushed out at least once a week to reduce mosquitoes near the paddock area. Work with your county mosquito control agency and point out any wetland habitats that may have produced the mosquito responsible for the infective bite.

What Should I Do If My Horse Develops Symptoms?

Suspect horse cases should be reported to your veterinarian as soon as possible. Your veterinarian will diagnose the infection and take blood or tissue samples for confirmation. Euthanasia may be necessary because the disease is fatal in unvaccinated animals. The veterinarian will probably request the brain since brain tissue is the only certain way to confirm the diagnosis. Some horse owners are reluctant to report suspect cases for fear of quarantine. There is no quarantine for EEE and non-reporting only postpones the mosquito control activities that could protect other horses on your farm and the immediate vicinity. The cycle of EEE is not yet completely understood. Quick reporting of a suspect case could provide valuable information for the future.

Thanks are due to the New Jersey Mosquito Control Association, Inc., who contributed funds to defray the cost of this fact sheet.

New Jersey Agricultural Experiment Station Publication No. H-40101-02-93 supported by State funds

Rutgers Cooperative Extension

N.J. Agricultural Experiment Station

Rutgers, The State University of New Jersey , New Brunswick

Distributed in cooperation with U.S. Department of Agriculture in furtherance of the Acts of Congress of May 8 and June 30, 1914. Cooperative Extension works in agriculture, family and consumer sciences, and 4-H. Zane R. Helsel, director of Extension. Rutgers Cooperative Extension provides information and educational services to all people without regard to sex, race. color, national origin. disability or handicap, or age. Rutgers Cooperative Extension is an Equal Opportunity Employer.