ISRAEL JOURNAL OF
VETERINARY MEDICINE
COMPLICATED STRANGLES: TWO CASE REPORTS
AND A LITERATURE REVIEW
Vol. 58 (4) 2003
A. Kol1, O. Levi1, D. Elad2 and A. Steinman1
1. Koret School of Veterinary Medicine, Hebrew University of Jerusalem, P.O.B. 12, 76100
Israel.
2. Dept. of Bacteriology, Kimron Veterinary Institute, P.O.B. 12, 50250 Bet Dagan, Israel
Abstract
Streptococcus equi subsp. equi infection, commonly known as "strangles” is characterized b
nasal discharge that is eventually followed by abscessation of the lymph nodes of the head an
Morbidity is nearly 100% in susceptible populations while the mortality rate ranges from 0 to 10
due to complications.
We describe a severe case of S. equi lung abscessation and a case of mesenteric abscess
fillies. The two cases represent complicated cases seen during a large-scale outbreak that occ
Israel in 2002. The antibiotic susceptibility tests of 7 isolates of the microorganism carried out i
during this outbreak are presented and the recent literature on S. equi subsp. equi infection rev
Introduction
Streptococcus equi subsp. equi, a gram-positive bacterium, is the
causative agent of strangles. Two of the major virulence factors associated
with infection are the hyaluronic acid capsule and the surface antigen M protein, which are antiphagocytic (2).
S. equi subsp. equi adheres to the epithelial cells of the buccal and nasal
mucosa of the horse (1). Following adherence, S. equi subsp. equi attaches
to the cells on the tonsillar crypts and the ventral surface of the soft palate
and can be detected in the mandibular or retropharyngeal lymph nodes
several hours after infection. The organism slowly multiplies extracellulary
and attracts a large number of neutrophils (3). S. equi subsp. equi is not a
normal inhabitant of the equine upper respiratory tract and does not require
prior viral infection for successful colonization and infection (1).
Although strangles can occur in horses of any age, those less than one
year old were most commonly affected (4) and morbidity is nearly 100% in
susceptible populations.
The incubation period is between 2 and 6 days. The common clinical
signs include a febrile, serous nasal discharge that later becomes
mucopurulent, and evidence of intermandibular and/or retropharyngeal
lymphadenopathy. Lymph nodes are initially firm but become fluctuant
before rupturing at 7 to 10 days after the onset of clinical signs. The average
duration for the disease is 23 days (1).
A complication rate of up to 20% has been reported, with a mortality rate
as high as 40% of the complicated cases (3). The potential complications of
S. equi subsp. equi infection include internal abscessation, purpura
hemorrhagica, guttural pouch empyema, suppurative necrotic
bronchopneumonia, myocarditis with endocarditis, and laryngeal hemiplegia
(1,2,3). The most common complication is internal abscessation, often
referred toas “ bastard strangles”. The main locations of abscesses include
the lung, mesentery, liver, spleen, kidneys, and brain (3). The causes of
internal abscessation are not known, although inadequate antimicrobial
therapy during respiratory catarrh and lymphoid abscessation may be
contributory (2).
Strangles has been diagnosed in Israel for many years either in a
sporadic form or as localized outbreaks. During 2002 a large-scale outbreak
affecting hundreds of horses all over Israel was reported (personal
communication, Haik R., Avni G.). This outbreak renewed the debate
regarding treatment and preventive measures that should be taken to reduce
the spread of the disease. Most cases recovered uneventfully during the
2002 outbreak. However, several horses died due to complications (personal
communication, Haik R., Avni G.). We describe in detail two cases of
"bastard strangles" referred to the Koret School of Veterinary Medicine Veterinary Teaching Hospital (KSVM-VTH).
Case 1
A one-year-old filly pony was referred to the KSVM-VTH with the chief
complaint of severe dyspnea. One month prior to admission, many of the
horses on the farm including the filly, suffered from an undiagnosed upper
airway disease. All other horses recovered uneventfully. The filly
subsequently became weak and slightly dyspneic. The owner treated her
with intramuscularly procaine penicillin for several days.
On arrival, physical examination revealed cachexia, depression and mild
dehydration. The filly showed severe dyspnea with a purulent bilateral nasal
discharge.
Wheezes and crackles were auscultated on the left thorax caudal to the
heart. Radiology revealed (lateral view), caudally to the heart, a large
(18cmX10cm) egg shaped mass, with a straight horizontal line (fluid level)
between radiolucent (gas) and radiopaque (fluid/soft tissue) medium (fig. 1).
An ultrasound-guided aspiration from the mass yielded a flocculent turbid
cream-colored fluid that contained white flakes. Cytology of the aspirated
fluid showed numerous degenerated and disintegrated neutrophils with
nuclear striking and a small number of reactive macrophages showing
phagocytosis of neutrophils and debris. These findings led to a diagnosis of
an abscess. Complete blood count revealed elevated white blood cells
(WBC) of 25* 1000/µl (normal 5.4-14.3 *1000/µl) and elevated triglyceride
(Trg) - 392 mg/dl (normal 5.3-54 gr/dl).
S. equi subsp. equi, identified with the
APIStrep kit (bioMerieux, France), was
cultured from the aspirated fluid.
Antibacterial
susceptibility
was
determined by a standardized disc
susceptibility method (NCCLS). The
owner refused our recommendation for
surgical treatment and he treated the
pony with procaine penicillin (25,000
iu/kg bwt IM bid), to which the isolate
was found to be susceptible (Table 1). A
week later the owner reported that the
filly died. Necropsy was not carried out.
Fig 1: Chest X-Ray, lateral view, case 1
Table 1: Susceptibility of the S. equi subsp. equi isolated in those cases in comparison to other
isolations in Israel during
n
2002.Drug
Isol
ate 1
Isol
ate 2
Isol
ate 3
Isol
ate 4
Isol
ate 5
Isol
ate 6
Isol
ate 7
Penicillin
S
S
I
S
S
I
I
Ampicillin
I
S
I
S
I
I
S
Oxacillin
S
S
S
S
S
S
Cephalothi
S
S
S
S
S
S
S
S
S
S
S
S
S
S
Erythromy
S
I
S
I
S
I
S
Clindamyc
I
S
I
S
I
S
Sulfadiazi
I
S
S
R
I
S
S
Tetracycli
S
S
I
S
S
S
S
Neomycin
S
S
S
S
S
S
R
Gentamici
S
S
S
S
S
S
S
Ciprofloxa
cine
I
S
I
S
S
S
S
Amoxicilli
n/
clavulanic.
a.*
cin
in
ne/
Trimethop
rim
ne*
n
R: resistant, I: intermediate, S: susceptible
Isolate 1 - case 1
Isolate 2 - case 2
*- Not recommended for use in horses (13)
Case 2
A 15 month old Arabian filly was refered to the KSVM-VTH with the
complaint of abdominal mass that was palpated per rectum. The filly had
undergone medical treatment for intermittent mild colic for a week prior to
admission.
Two months before referral, a strangles outbreak occurred at the home
farm of the filly. At the time of the outbreak the filly had fever and nasal
discharge, she was treated with procaine penicillin (13,000 iu/Kg IM, bid) for
ten days. Following treatment the filly’s condition improved.
On arrival, physical examination revealed a bright and alert filly with no
abnormalities. On rectal examination a round firm mass with irregular
surface (25 cm diameter) was palpated connected with a pedicel to the
mesentery. Trans-rectal ultrasonography showed a fluid filled mass with
compartments with no peristalsis nor gas. A complete blood count revealed
elevated WBC- 25.43* 103/µl, slight anemia (microcytic anemia), low
hemoglobin (Hgb)- 7.6 gr/dl (normal 11-19 gr/dl) with mild elevation in total
solids (Ts)- 8.4 gr/dl (normal 5.7-7.9 gr/dl) and Globulin (Glb)- 5.2 gr/dl.
A peritoneal fluid sample was hazy yellow with a high cell count (WBC19.7*103/µl) and high Ts (3.6 gr/dl).
In an exploratory laparotomy, an abscess was found connected by a
pedicel to the mesentery of the jejunum. The abscess was not dissected
because of the proximity to large blood vessels and was therefore drained. A
Foley catheter was placed from the lumen of the abscess to the outside
through the ventral body wall. A second Foley catheter was placed from the
peritoneal cavity to the outside through the ventral body wall.
During surgery a fluid sample was aspirated from the abscess.
S. equi subsp. equi, identified with the APIStrep kit (bioMerieux, France),
was cultured from the aspirated fluid. Antibacterial susceptibility was
determined by NCCLS.
Post-operatively the abdomen was flushed once (using 10 liters of saline)
and the peritoneal Foley catheter removed. The abscess was flushed for five
days (twice a day) using 2% povidone iodine solution, and the Foley catheter
removed when clean fluid was flushed out of the abscess twice.
Medical treatment included flunixin meglumine (0.5-1 mg/kg I.V bid) for five
days, gentamicin (6.6 mg/kg I.V sid), penicillin G (40,000 iu/kg I.V qid) until
discharge (10 days) and procaine penicillin (20,000 iu/kg I.M bid) for another
ten days.
Trans rectal ultrasonography before discharge revealed a marked
decrease in the mass diameter (10 cm).
On discharge the filly was bright and alert and did not show signs of colic but
the WBC remained elevated (14.5*103/µl). Three weeks later the WBC was
within normal limits (7.5*103/?l).
Discussion
As early as 1664, Solleysel, concerned about the contagious nature of
strangles, recommended isolation of affected animals and pointed out that
the commonest source of infection for horses was water buckets (3).
Persistence in affected herds may be due to survival of S. equi subsp. equi
either in carrier hosts or in the environment. Recent epidemiological
investigation by Newton et al in 1999, provide further evidence that a carrier
state can be responsible for the persistence of S. equi subsp. equi between
outbreaks. In these cases the guttural pouches were found to be the sites of
carriage and the mean duration of carriage was 19 months (5).
Both cases have the same characteristics and they fit the literature, the
only difference is the method of treatment and the final outcome. Fillies with
“bastard strangles,” that was diagnosed after an inadequate antimicrobial
therapy, is described in both cases. They suffered from a large internal
abscess that interrupted the function of an adjacent organ, and they both
had elevated WBC.
The filly that underwent surgical treatment followed by an aggressive
medical treatment survived in contrast to the second filly that was treated
medically and died.
S. equi subsp. equi infection is a very contagious disease, therefore
proper treatment and measures for preventing the spread of the disease are
important. Although it is a well known disease there is a debate and
uncertainty regarding its treatment. It is generally agreed that treatment is a
function of the stage of the disease, of both the individual horse and the
whole stable.
How to treat the individual horse?
1. Horses with early signs of strangles (including pyrexia and
depression, without abscessation of the lymph nodes) should be
isolated. The disease can be arrested at this time with antimicrobial
treatment. The drug of choice is penicillin (procaine penicillin 22,000
iu/kg IM bid, for 5 days after complete resolution of clinical signs) (6),
but according to the tests carried out in the Department of
bacteriology, Kimron Veterinary Institute, S. equi subsp. equi was
susceptible also to oxacillin, cephalothin and gentamicin (table 1).
However, there is a high probability of relapse following cessation of
therapy, because protective immune responses are poor in
antimicrobially treated horses (3). Inadequate antimicrobial therapy
may be contributory to the formation of “bastard strangles”.
2. Horses with lymph nodes abscessation. Therapy should be
directed toward enhancing maturation and drainage of the abscess
(3). The administration of antimicrobial medication may slow down the
progres of the abscessation and is generally contraindicated. In
contrast, a recent study showed that IM administration of 20,000 iu/Kg
of procaine penicillin G given every 24 h for 21 days eliminated
Streptococcus equi subsp. zooepidemicus from an abscess model
(tissue chambers) in seven out of eight ponies (7). When an abscess
is draining, it should be flushed regularly with a 2-5% povidone-iodine
solution (6).
3. Horses exposed to strangles - Antimicrobial therapy can
prevent an exposed horse or foal from contracting strangles during
the period of therapy (1,3). Penicillin therapy (procaine penicillin
22,000 iu/kg IM bid) may be effective if exposure to the organism can
be ceased before the end of therapy.
4. Horses with a complication - These horses should be treated
immediately aggressively and specifically, including surgical
procedures (4).
How to control an outbreak?
Healthy carriers of S. equi subsp. equi have long been regarded as
a problematic source of “strangles” in susceptible animals(8). The
predominant sites of carriage are the guttural pouches (9). The first
control measure for arresting the spread of the disease is to prevent
movement of horses between farms and to isolate all clinical cases
and healthy carriers. Flies may serve as mechanical vectors and
efforts to control the fly population should be made during an
outbreak. An asymptomatic carrier is defined as one from which S.
equi subsp. equi is cultured from at least one of three weekly
nasopharyngeal swabs and the animal has no clinical signs of
strangles (5). All asymptomatic carriers were found to have lesions in
their guttural pouches including empyema and chondroids (9). The
mean duration of carriage was 19 months (5).
For early identification of clinical cases the rectal temperature is
measured once or twice daily. In infected stables, any elevation of
rectal temperature is suggestive of a S. equi subsp. equi infection. S.
equi subsp. equi can be demonstrated by culture or by polymerase
chain reaction (PCR) of nasal swabs or guttural pouch aspirations.
Elimination of guttural pouch infection in asymptomatic carriers can be
achieved by alleviating the inflammatory pathology by flushing the guttural
pouches, combined with systemic and topical use of an antibiotic (8).
Surgery is recommended in cases in which both pharyngeal openings of
the guttural pouches are occluded or in cases in which medical treatment
was not satisfactory.
Vaccination
Most vaccines available incorporate inactivated whole cells or M-protein
extract (10) and adverse reactions were seen after their administration.
Local reactions of firm edematous swellings account for 72% of the reported
cases, while systemic signs of arthritis, stiffness, lameness, founder and
lethargy were described in 24%. Fever, respiratory signs, colic, ataxia and
edema of ventral abdomen and lower legs are less frequent. Purpura
haemorrhagica was reported after use of a whole cell vaccine (11). The
prevalence of an adverse reaction has not been clearly established, but it
can be as high as 5% (12). Immunity is obtained in less than half of the
vaccinated animals, and then only when the components were incorporated
in an adjuvant or when multiple injections were given (2). Following recovery
from an outbreak of strangles, approximately 75% of the infected animals
have an extended period of resistance to re-infection. Moreover, there is
evidence that for protection, a mucosal immune response rather than a
systemic one is needed (10). One study showed that a live attenuated S.
equi subsp. equi vaccination administered in the sub-mucosa (of the upper
lip) appeared to be efficacious with a side effect of a transient reaction at the
site of injection (10). It seems that we will have to wait for better and safer
vaccines.
LINKS TO OTHER ARTICLES IN THIS ISSUE
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