Changes

====Clinical Signs====

====Clinical Signs====

The incubation of the disease after infection with the virus is from 1 to 3 weeks. In the initial stage there is fever, which may be accompanied by depression, and loss of appetite, but the reaction may be so mild it goes unnoticed. The virus causing Eastern Equine Encephalomyelitis (EEE) is the most virulent of the three types and the symptoms produced are the most severe, with a case fatality rate of up to 90%. The viraemia (level of virus in the blood) may be so high with this strain that horse to mosquito to horse cycling can occur.

The virus causing Eastern Equine Encephalomyelitis (EEE) is the most virulent of the three types and the symptoms produced are the most severe, The viraemia (level of virus in the blood) may be so high with this strain that horse to mosquito to horse cycling can occur.

The nervous signs, when they appear, are hypersensitivity to sound and touch with periods of excitement and restlessness with apparent blindness. Affected horses may walk blindly into objects or walls. Muscle twitchings may occur in the face and shoulder muscles. A period of severe depression follows. Affected horses stand with their heads hung low and may have a half-chewed mouthful of feed hanging from their lips. The animal appears to be asleep and is unable to hold up his head and often rests it on some solid object.

Muscle twitchings may occur in the face and shoulder muscles. A period of severe depression follows. Affected horses stand with their heads hung low and may have a half-chewed mouthful of feed hanging from their lips. The animal appears to be asleep and is unable to hold up his head and often rests it on some solid object.

Although VEE does not cause as high a mortality as WEE/EEE, the clinical signs are similar. However, a second generalised infection may be caused by the virus causing fever, depression, colic and diarrhoea.

Although VEE does not cause as high a mortality as WEE/EEE, the clinical signs are similar. However, a second generalised infection may be caused by the virus causing fever, depression, colic and diarrhoea.

Worse in unvaccinated animals.   

Worse in unvaccinated animals.   

=====EEE and WEE=====

=====EEE and WEE=====

Acute signs are nonspecific and last up to 5 days:

Following an incubation period of 7-21days, an initial pyrexia and mild depression are short-lived and often missed.  The acute phase of the disease presents with mild to severe pyrexia, anorexia and stiffness, lasting up to 5 days.  During this time, the horse is viraemic and capable of amplifying the disease.  The fever may then fluctuate with neurological derangements appearing a few days post-infection.  These changes indicate disease progression, which occurs more frequently with EEE.  Any of the following may be observed:

*mild to severe pyrexia

*anorexia

*stiffness

Early signs transient and often missed:

*fever may rise and fall sporadically

Cerebral signs often occur a few days post-infection (but can occur at any time.  In the acute phase the following may be noted:

*propulsive walking

*propulsive walking

*depression

*depression

*somnolence

*somnolence

*hyperaesthesia

*aggression

*excitability

*excitability

*frenzy in response to sensory stimulation

*restlessness

*conscious proprioceptive deficits

*hypersensitivity to sound and touch

With progression, worsening cerebral cortical and cranial nerve dysfunction may result in:

Worsening neurological deficits may result in:

*head pressing

*head pressing

*propulsive walking

*head tilt

*circling

*circling

*head tilt

*apparent blindness

*facial and appendicular muscle fasciculations

*facial and appendicular muscle fasciculations

*paralysis of pharynx, larynx and tongue

*pharynx, larynx and tongue paralysis

*recumbency for 1-7 days followed by death

*recumbency for 1-7 days followed by death