EQUINE | Equine Disease Quarterly
France reported equine piroplasmosis was endemic
in the country. The RSA recorded several cases of the
disease in four provinces.
Taylorella equigenitalis, the causal agent of contagious
equine metritis was detected in an aged stallion in
France, and in six stallions and one mare on a total of
six premises in Germany.
A single case of equine coital exanthema caused by
EHV-3 was diagnosed in a mare in Kentucky.
A number of cases of nocardioform placentitis were
reported by the USA, several involving infection with
Amycolatopsis spp and an additional group associated
with Crossiella equi infection, all but one in Kentucky.
The USA confirmed 11 cases of salmonellosis during
the review period, all isolates belonging to serogroup
B.
Three cases of Clostridium perfringens Type A toxin
genotype were diagnosed in foals in Kentucky.
Germany confirmed rotavirus infection in two foals on
the same premises.
A case of Lawsonia intracellularis infection was
diagnosed in a foal in Kentucky.
The USA recorded four cases of Eastern Equine
Encephalomyelitis (EEE) in the first quarter of 2018, all
in Florida.
Equine encephalosis was reported by the RSA, with
numerous cases in one province and isolated cases in
three other provinces.
Rhodococcus equi infection is endemic in the USA,
with many cases going unreported.
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Insect Bite Hypersensitivity in Horses
A large percentage of horses affected with seasonal
pruritic dermatitis are hypersensitive (allergic) to the
bites of insects. Culicoides spp (gnats), black flies,
stable flies, and horn flies are the most commonly
implicated insects although any biting insect may
contribute to insect bite-induced hypersensitivity
(IBH). IBH is characterized by intense pruritus
(itching) that often leads to excoriation (abrasive skin
damage), extensive hair loss, secondary infections,
and chronically to hyperkeratosis and lichenification
(thickened skin). Many horses develop IBH in middle
age or later, although horses with atopy may exhibit
clinical signs as early as 1 year of age. Clinical signs
often progress in each subsequent year.
Diagnosis is made from the signalment, history,
clinical signs, and ruling out of other possible
diagnoses. The distribution of lesions on an
affected horse with IBH is dependent on the biting
characteristics of the insect(s) responsible. Since there
is still much to be learned about the identification and
feeding habits of many insects implicated in allergic
dermatoses, it may not be possible to identify the
exact etiological agent(s). IBH typically improves and
exacerbates seasonally, whereas clinical expression
of allergies in atopic horses may occur at any time of
the year. Urticaria (hives), commonly found in atopy,
is not a diagnosis but a cutaneous reaction pattern
that may be induced by a wide variety of causes, both
immunologic and non-immunologic. Rule outs for
urticaria include drug and vaccine reactions; stinging
and biting insects (such as wasps) and arachnids;
infections; contact irritation; vasculitis; and cold,
stress, or exercise-induced lesions. Other diseases that
exhibit pruritus are Oxyuris (pin worm) infestation,
onchocerciasis, and mite (Chorioptes) and tick
infestations. Diseases that occasionally are associated
with pruritus include ringworm and pemphigus, an
• Equine Health Update •