Published Date: 2008-05-03 17:00:20
Subject: PRO/AH/EDR> Strangles, equine - India (Maharashtra)
Archive Number: 20080503.1519
STRANGLES, EQUINE - INDIA (MAHARASHTRA)
A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
Date: Fri 2 May 2008
Source: The Hindu [edited]
Shifting of horses delayed
Shifting of the horses from Mumbai [Bombay] to Pune [Poona] has been
delayed by a few weeks as 12 horses are feared to be affected by the
Mr. Vivek Jain, Chairman, Media & Marketing Committee, RWITC [The
Royal Western India Turf Club Limited], said that "the shifting of
horses has been stopped for a few weeks as a precautionary measure,
as the disease is contagious.
Also the Bangalore Turf Club has stopped any horses coming from
Mumbai till they get clearance report from RWITC. This disease is
curable and not fatal and I hope shifting should start after a few weeks."
[Strangles, a globally distributed equine infection, is not included
in OIE's list of notifiable diseases; and it is not zoonotic.
The following data are derived from the chapter "Respiratory diseases
of horses - Strangles" in Merck Veterinary Manual (9th edition, 2005):
Strangles is an infectious, contagious disease of Equidae
characterized by abscessation of the lymphoid tissue of the upper
respiratory tract. The causative organism, _Streptococcus equi equi_,
is highly host-adapted and produces clinical disease only in horses,
donkeys, and mules. It is a gram-positive, capsulated-hemolytic
Lancefield group C coccus, which is an obligate parasite and a primary
Etiology and Pathogenesis:
_S equi equi_ is highly contagious, and produces high morbidity and
low mortality in susceptible populations. Transmission occurs via
fomites and direct contact with infectious exudates. Carrier animals
are important for maintenance of the bacteria between epizootics and
initiation of outbreaks on premises previously free of disease.
Survival of the organism in the environment is dependent on
temperature and humidity; it is susceptible to desiccation, extreme
heat, and exposure to sunlight, and must be protected within mucoid
secretions to survive. Under ideal environmental circumstances, the
organism can survive 7-9 wk outside the host. Paddocks and barn
facilities used by infected horses should be regarded as contaminated
for about 2 months after resolution of an outbreak.
The incubation period of strangles is 3-14 days and the 1st sign of
infection is fever (103-106 F [39.4-41.1 C]). Within 24-48 hr of the
initial fever spike, the horse will exhibit signs typical of
strangles, including mucoid to mucopurulent nasal discharge,
depression, and submandibular lymphadenopathy. Horses with
retropharyngeal lymph node involvement will have difficulty
swallowing, inspiratory respiratory noise (compression of the dorsal
pharyngeal wall), and extended head and neck. Older animals with
residual immunity may develop an atypical or catarrhal form of the
disease with mucoid nasal discharge, cough, and mild fever.
Metastatic strangles ('bastard strangles') is characterized by
abscessation in other lymph nodes of the body, particularly the lymph
nodes in the abdomen and, less frequently, the thorax.
Diagnosis is confirmed by bacterial culture of exudate from abscesses
or nasal swab samples. CBC reveals neutrophilic leukocytosis and
hyperfibrinogenemia. Serum biochemical analysis is typically
unremarkable. Complicated cases may require endoscopic examination of
the upper respiratory tract (including the guttural pouches),
ultrasonographic examination of the retropharyngeal area, or
radiographic examination of the skull to identify the location and
extent of retropharyngeal abscesses.
The environment for clinically ill horses should be warm, dry, and
dust-free. Warm compresses are applied to sites of lymphadenopathy to
facilitate maturation of abscesses. Facilitated drainage of mature
abscesses will speed recovery. Ruptured abscesses should be flushed
with dilute (3-5 percent) povidone-iodine solution for several days
until discharge ceases. NSAID can be administered judiciously to
reduce pain and fever and improve appetite in horses with fulminant
Antimicrobial therapy is controversial. Most authors agree that
initiation of antibiotic therapy after abscess formation may provide
temporary clinical improvement in fever and depression, but
ultimately prolongs the course of disease by delaying maturation of
abscesses. Antibiotic therapy is indicated in cases with dyspnea,
dysphagia, prolonged high fever, and severe lethargy/anorexia.
Administration of penicillin during the early stage of infection (24
hr of onset of fever) will usually abort abscess formation. The
disadvantage of early antimicrobial treatment is failure to mount a
protective immune response, rendering horses highly susceptible to
infection after cessation of therapy. If antimicrobial therapy is
indicated, procaine penicillin is the antibiotic of choice.
Postexposure immunity is prolonged after natural disease in most
horses, and protection is associated with local (nasal mucosa)
production of antibody against the antiphagocytic M protein. The
clinical attack rate of strangles is reduced by 50 percent in horses
vaccinated with IM products that do not induce mucosal immunity.
Local (mucosal) production of antibody requires mucosal antigen
stimulation. An intranasal vaccine containing a live attenuated
strain of _S equi equi_ was designed to elicit a mucosal immunologic
response. This attenuated strain is not temperature sensitive
(inactivated by core body temperature), like the intranasal influenza
vaccine. Reported complications include _S equi equi_ abscesses at
subsequent IM injection sites (live culture), submandibular
lymphadenophathy, serous nasal discharge, and purpura hemorrhagica.
Clinically affected horses should be physically separated from the
herd and cared for by separate caregivers. The rectal temperature of
all horses exposed to strangles should be obtained twice daily, and
horses developing fever should be isolated (and potentially treated
with penicillin). Contaminated equipment should be cleaned with
detergent and disinfected using chlorhexidine gluconate or
glutaraldehyde. Flies can transmit infection mechanically; therefore,
efforts should be made to control the fly population during an
outbreak. Farriers, trainers, and veterinarians should wear
protective clothing or change clothes prior to traveling to the next
equine facility. Additions to the herd should be carefully
scrutinized for evidence of disease or shedding (nasopharyngeal
culture) and quarantined for 14-21 days. Two negative nasal swab
cultures should be obtained during the quarantine period.
Most horses continue to shed _S equi_ for about 1 month following
recovery. Three negative nasopharyngeal swabs, at 4-7 days intervals,
should be obtained prior to release from quarantine, and the minimum
isolation period should be 1 month. Prolonged bacterial shedding (up
to 18 months) has been identified in a small number of horses.
Guttural pouch empyema is the source of infection in most prolonged
carrier states. Bacterial culture of nasopharyngeal swab and/or
guttural pouch lavage is used to identify persistent carriers.
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