Infectious Diarrhea in Foals

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IN DEPTH: CURRENT CONCEPTS IN PEDIATRICS
Infectious Diarrhea in Foals
Guy D. Lester, BVMS, PhD, Diplomate ACVIM
Author’s address:
Alec P. and Louise H. Courtelis Equine Teaching Hospital, College of Veterinary
Medicine, University of Florida, Gainesville, FL 32610-0136.
© 2001 AAEP.
1.
Introduction
rhea, or does it merely re?ect a change in normal
The range of infectious agents that cause diarrhea in
?ora and bacterial shedding in response to changes
foals is poorly described, at least when compared to
induced by a different pathogen?
Controlled inoc-
other domesticated species.
Recently, several new
ulation studies are required to verify a more de?ni-
agents have been incriminated as causes of diarrhea
tive role for some of these potential pathogens.
in newborn and suckling foals.
In addition, there
In addition, the recovery of two or more potential
are new diagnostic tests available that may aid in
intestinal pathogens from foals with diarrhea is not
differentiating new and established causes of diar-
uncommon.
rhea.
Many of these tests involve primary bacterial
culture with subsequent molecular analysis.
2.
Speci?c Agents Associated with Infectious Foal
The approach to diagnosis requires knowledge of
Diarrhea
likely pathogens, what tests are available, and how
to interpret data from the lab.
In addition, the type
Anaerobic Bacterial Pathogens
of samples to be requested should be guided by the
Intestinal Clostridiosis
animal’s age, the number of foals affected, and phys-
ical examination ?ndings.
The common causative agents of this condition are
Isolation of an organism from the feces of foals
Clostridium perfringens biotypes A and C and Clos-
with diarrhea does not directly indicate that the
tridium dif?cile.
These gram-positive organisms
diarrhea is caused by that agent.
Clostridium per-
can be found in the intestinal tracts of domestic
fringens (biotype A), Rhodococcus equi, Bacteroides
animals and are widely distributed throughout the
fragilis, and rotavirus are examples of potential en-
environment, including the soil.
They produce po-
teric pathogens that may be recovered from feces in
tent exotoxins that are responsible for a variety of
the absence of disease.
Unfortunately, our knowl-
intestinal diseases in domestic animals.
Enteric
edge of normal ?ora or changes that occur in the
disease induced by Clostridium species are recog-
?ora in response to disease is lacking.
For exam-
nized more commonly during the early neonatal pe-
ple, does the fact that Aeromonas hydrophila is more
riod and there are reports of biotypes A, B, C, D, and
frequently recovered from the feces of foals with
E being associated with enteric disease of foals; most
diarrhea than from those of healthy animals1 indi-
studies suggest that biotypes A and then C are the
cate that this bacterium is responsible for the diar-
most important.2
NOTES
468
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IN DEPTH: CURRENT CONCEPTS IN PEDIATRICS
Classically, disease induced by C. perfringens bio-
with that toxin.
This organism has been isolated
type C is associated with hemorrhagic diarrhea, ab-
both from adult horses and foals with diarrhea.
dominal distention, colic, circulatory shock, and
Toxin assays.
Samples should be delivered di-
high mortality.
Disease often occurs within the
rectly to a diagnostic laboratory immediately or
?rst 48 hours of life and is most commonly seen in
transported on ice and shipped overnight.
The tra-
vigorous foals with high milk intake.
The diagno-
ditional method for toxin identi?cation within in-
sis is con?rmed by identifying the toxin within the
testinal contents or fecal samples is by mouse
feces or intestinal lumen (by mouse inoculation).
inoculation.
Commercial assays for C. dif?cile tox-
Recovery of the organism and biotyping by toxin
ins A or B are reliable if the samples are handled
gene identi?cation (PCR) may increase the accuracy
appropriately.
An additional commercial assay is
of diagnosis short of toxin identi?cation.
Treat-
available for C. perfringens enterotoxin (CPE) but
ment is often unrewarding but should consist of
concerns exist as to sensitivity, speci?city, and the
antimicrobial agents (including potassium or so-
positive predictive value of this test in clinical cases.
dium penicillin and metronidazole), nonsteroidal
Gram stain of feces.
Large numbers of gram-pos-
anti-in?ammatory agents, plasma, and C. perfrin-
itive rod-shaped bacteria are seen on fecal gram
gens biotype C antitoxin.
Total parenteral nutri-
stain.
Spore stains can be requested but rarely
tion should be considered if aggressive treatment is
provide useful additional data.
pursued.
Probiotics may be bene?cial as part of a
Blood culture.
Highly recommended in young
treatment protocol or as preventative therapy in
foals because many foals are bacteremic with C.
other newborn foals on the property.
Anecdotal
perfringens (usually biotype A) and, rarely, C.
success has been reported with the use of commer-
dif?cile.
cial type C & D toxoid in pregnant mares.
In recent years, an emergence of enteric disease
Bacteroides fragilis
associated with C. perfringens biotype A has been
It is likely that Bacteroides fragilis, a gram-negative
seen in newborn foals.
Clinical signs are variable
anaerobic rod, is an intestinal pathogen of foals.
but may include transient bloody stool, colic, and
Unfortunately, isolation of the organism from diar-
fever.
Mortality is reduced when compared with
rhea samples does not con?rm diagnosis because the
disease induced by C. perfringens biotype C.
The
bacterium occurs both in enterotoxigenic and non-
role of this biotype is frequently confounded because
toxigenic forms.
Enterotoxigenic strains of B. fra-
it appears to be commonly present in the feces of
gilis are associated with diarrhea in several species,
healthy young foals.2
including lambs, calves, pigs, humans, and foals.4
Likewise, the role of C. dif?cile in juvenile diar-
These pathogenic strains are noninvasive but pro-
rhea is not clear.
A well-de?ned cause of neonatal
duce a ?20 kD heat-labile toxin that induces muco-
enterocolitis in foals less than 4 days old, this organ-
sal in?ammation.
Limited data from foals indicate
ism has received a lot of attention in recent years as
that B. fragilis is commonly isolated with other
a potential enteric pathogen of adult horses.
pathogens.
Prevalence varies with geographic location but C.
Diagnosis is achieved by culturing the organism
dif?cile appears to be a rare isolate in older suckling
and then verifying toxin-producing strains with ar-
foals.
Treatment is as for C. perfringens biotype C
bitrarily primed PCR or, more traditionally, with
minus the commercial type C & D antitoxin.
isolated intestinal loop inoculation.5
Treatment in-
Fecal culture.
Samples should be collected and
volves administration of metronidazole and support-
shipped in an appropriate container (Port-a-Cul an-
ive therapy.
aerobic tubes).a
The isolation of C. dif?cile is usu-
ally considered signi?cant in foals of all ages but it is
Aerobic Bacterial Pathogens
not uncommon to identify foals that are culture-
positive but toxin-negative.3
Recovery of C. per-
Salmonellosis
fringens from diarrheic foals is also of questionable
Spectacular outbreaks of salmonellosis are possible
signi?cance because the organism, particularly C.
in horses of any age6 but most occurrences in foals
perfringens biotype A, is commonly present in the
occur as isolated cases.
The mare appears to be the
feces of healthy foals.
primary source of infection and both the dam and
Identi?cation.
The genes that encode the Clos-
the foal usually are fecal-positive for the pathogen.
tridial toxins can be ampli?ed and categorized using
It is rare for both to demonstrate signs of disease.
PCR techniques.
All C. perfringens isolates contain
Most affected foals have moderate-to-severe clinical
an alpha toxin.
Further separation into biotypes A
signs that include fever, diarrhea, dehydration, pro-
through E is based on the identi?cation of additional
found depression, and reduced appetite.
Diarrhea
toxins produced by the bacteria.
The exception is a
can vary both in consistency and volume and may
C. perfringens isolate that is yet to be biotyped but
contain blood.
Colic is common in the early stages
that contains the alpha toxin and a ?2 toxin. The
of the disease.
A complete blood count usually re-
latter toxin has biological activity similar to the ?
veals neutropenia with a left shift and toxicity,
toxin but has no signi?cant amino acid homology
which is replaced by a rebound neutrophilia as the
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IN DEPTH: CURRENT CONCEPTS IN PEDIATRICS
disease becomes chronic.
The ?brinogen usually is
heavy growth of mucoid E. coli on agar plates would
elevated.
increase the level of suspicion.
Extraintestinal disease as a consequence of bacte-
remia is common in foals less than 2 months old.
Enterococcus (Group D Streptococcus) durans
These extraintestinal diseases include bacterial uve-
This organism has been implicated as a cause of
itis, infectious synovitis, osteomyelitis, pneumonia,
diarrhea in several species, including foals, pigs,
and meningitis.
calves, and pups.9
Enterococcus durans is com-
Blood culture.
This is particularly useful in foals
monly isolated from the feces of young foals with
less than 1 month old because young foals with
diarrhea, although often with other potential patho-
intestinal salmonellosis frequently are bacteremic.
gens.
Tzipori and colleagues9 concluded that the
Fecal culture.
Transport using suitable media
organism colonized the small intestinal mucosa and
(e.g., Ames aerobic culture media).b
Samples can
was associated with mild-to-moderate pathology.
be transported in selenite broth if processed within
It is therefore likely that the severity of diarrhea
24 hours after collection.
would be inversely related to age.
Fecal PCR.
This technique appears to be highly
sensitive and a positive result may carry greater
Rhodococcus equi
importance in a foal than in an adult horse with
Rhodococcus equi infection of the respiratory tract is
diarrhea.
frequently associated with changes within the Peyer’s
Treatment.
In contrast to adults, most foals with
patches and mesenteric lymph nodes, but diarrhea
Salmonella infection require aggressive and early
is rare.
There is a syndrome of ulcerative entero-
antibiotic treatment.
Appropriate ?rst-line choices
colitis attributed to R. equi but establishing an an-
include third-generation cephalosporins or amino-
temortem diagnosis is dif?cult because fecal culture
glycosides, which should be guided by sensitivity
of the organism is common.
patterns.
Unfortunately, secondary sites of infec-
tion, particularly osteomyelitis, may develop and
Other Aerobic Bacteria Implicated in
persist in the presence of antibiotic therapy.
These
Infectious Diarrhea
complications may not be detected clinically for
These bacteria include Aeromonas hydrophila, Yer-
weeks after the onset of enteric disease.
Bismuth
sinia enterocolitica, and Campylobacter species.
subsalicylate is commonly used in foals with diar-
Much of the data incriminating Aeromonas hy-
rhea.
Its antidiarrheal action is achieved by stim-
drophila as a potential pathogen of foals stems from
ulation of ?uid and electrolyte absorption and by
work done in the UK in the early 1990s.1
inhibiting the synthesis of the prostaglandins (when
hydrolyzed to salicylic acid) involved in intestinal
Viral Intestinal Disease
in?ammation.
Bismuth subsalicylate also binds
Rotavirus
bacterial toxins and is thought to have a bactericidal
action.
The use of motility-modifying agents such
Group A rotavirus is the most common cause of
as atropine or loperamide is contraindicated in foals
infectious diarrhea in foals.
Typically, several foals
with enteric infections where bacteria or bacterial
are affected over a short period of time.
The dis-
toxins may invade or damage the intestinal mucosa
ease is highly contagious and has a very short incu-
(e.g., clostridial infections or Salmonella).
Loper-
bation period.
Severity of disease is determined by
amide may be useful in other forms of diarrhea but
immune status, inoculation dose, and, most impor-
prolonged use is not recommended.
If clinical im-
tantly, age.
The basis of the diarrhea is not fully
provement is not apparent by 48 –72 hours, further
known but it likely involves brush border enzyme
use is unlikely to be helpful.
de?ciency, which leads to inadequate digestion of
substrate and osmotic diarrhea in the colon.
Re-
cent attention has been given to the membrane-
Escherichia coli
spanning nonstructural glycoprotein NSP4 as a
Escherichia coli is the most common cause of sys-
potential viral cytotoxin and enterotoxin.
The en-
temic sepsis in newborn foals but it is an uncommon
terotoxin is released from rotavirus-infected entero-
primary enteric pathogen.
There are reports that
cytes and is a speci?c noncompetitive inhibitor of the
suggest that E. coli can mediate diarrhea in foals
Na(?)-D-glucose symporter. The protein also en-
less than one month old.
The diarrhea is profuse
hances chloride secretion through a signal transduc-
and
watery
but
nonfetid.7
Enteropathogenic
tion pathway.10
strains of E. coli (0111a, K792) caused classical ul-
The diagnosis of rotavirus is often made on the
trastructural changes to the intestinal microvilli of
basis of epidemiological ?ndings (large number of
ileal explants harvested from month-old foals.8
cases), physical examination ?ndings (diarrhea, de-
Recovery of E. coli from feces is very common but
pression, or reduced appetite, with or without fever),
these isolates typically lack the appropriate viru-
and samples from representative animals.
Fecal
lence factors required to create intestinal disease.
antigen tests (e.g., Virogen Rotatest and Rotazyme)c
Diagnosis is achieved by culture from feces and
are sensitive and provide rapid con?rmation.
Sub-
then detecting virulence factors with PCR.
A
mitting fecal samples for electron microscopy (EM)
470
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IN DEPTH: CURRENT CONCEPTS IN PEDIATRICS
is also an effective means of establishing a
monly, this is a state-run diagnostic laboratory.
diagnosis.
It is also critical to consider likely differentials when
Treatment of rotaviral diarrhea is supportive and
requesting tests and to understand the relevance of
uses a combination of intravenous and oral replace-
a positive test result.
Treatments continue to be
ment ?uids.
Antibiotics are not indicated unless
primarily supportive but often include metronida-
the foal is less than 2 weeks old.
A maternal vac-
zole or speci?c antibiotic therapy if salmonella is
cine is available and may confer modest protection.
identi?ed.
Coronavirus
There are recent reports of coronavirus acting as a
References and Footnotes
primary pathogen in young immunocompetent
1. Browning GF, Chalmers RM, Snodgrass DR, et al.
The
foals.11,12
Previously, foals with immune dysfunc-
prevalence of enteric pathogens in diarrhoeic thoroughbred
foals in Britain and Ireland.
Equine Vet J 1991;23:405– 409.
tion, such as severe combined immunode?ciency dis-
2. Netherwood T, Wood JLN, Mumford JA, et al.
Molecular
ease (SCID) Arabian foals, were considered to be at
analysis of the virulence determinants of Clostridium perfrin-
greatest risk.
It is unlikely that coronavirus infec-
gens associated with foal diarrhea.
Vet J 1998;155:289 –294.
tion is responsible for outbreaks of foal diarrhea.
3. Weese JS, Staemp?i HR, Prescott JF.
A prospective study of
There have also been reports, published and unpub-
the roles of clostridium dif?cile and enterotoxigenic Clostrid-
ium perfringens in equine diarrhoea.
Equine Vet J 2001;33:
lished, of parvovirus and breda virus causing diar-
403– 409.
rhea in foals.
4. Sarma PN, Tang YJ, Prindiville TP, et al.
Genotyping of
Bacteroides fragilis isolates from stool specimens by arbi-
Protozoan Intestinal Diseases
trarily-primed-PCR.
Diagn Microbiol Infect Dis 2000;37:
225–229.
Cryptosporidium
5. Myers LL, Shoop DS, Byars TD.
Diarrhea associated with
enterotoxigenic Bacteroides fragilis in foals.
Am J Vet Res
The role of cryptosporidium in foal diarrhea remains
1987;48:1565–1567.
controversial.
Infection rates have been reported
6. Walker RL, Madigan JE, Hird DW, et al.
An outbreak of
between 15% and 31% in suckling foals.13
Crypto-
equine neonatal salmonellosis.
J Vet Diagn Invest 1991;3:
sporidium has been associated with fatal outcomes
223–227.
in foals.14
Foals at greatest risk for cryptospo-
7. Holland RE, Sriranganathan N, DuPont L.
Isolation of en-
terotoxigenic Escherichia coli from a foal with diar-
ridium-induced diarrhea are those with primary im-
rhea.
J Am Vet Med Assoc 1989;194:389 –301.
munode?ciencies.
There
are
several
methods
8. Batt RM, Embaye H, Hunt J, et al.
Ultrastructural damage
commonly used to detect oocysts in fecal samples,
to equine intestinal epithelium induced by enteropathogenic
including acid-fast staining, immuno?uorescence
Escherichia coli.
Equine Vet J 1989;21:373–375.
assays, and ?ow cytometry.
Acid-fast staining is
9. Tzipori S, Hayes J, Sims L, et al.
Streptococcus durans:
an unexpected enteropathogen of foals.
J Infect Dis 1984;
very sensitive but is less speci?c than the other
150:589 –593.
techniques.15
Submission of fecal samples to a lab-
10. Halaihel N, Lievin V, Ball JM, et al.
Direct inhibitory effect
oratory should speci?cally state that detection of
of rotavirus NSP4(114 –135) peptide on the Na(?)-D-glucose
cryptosporidium is required because expertise usu-
symporter
of
rabbit
intestinal
brush
border
mem-
ally is necessary to detect the small oocysts.
brane.
J Virol 2000;74:9464 –9470.
11. Guy JS, Breslin JJ, Breuhaus B, et al.
Characterization of a
Treatment is generally supportive and centers on
coronavirus isolated from a diarrheic foal.
J Clin Microbiol
?uid and electrolyte replacement.
Speci?c drug
2000;38:4523– 4526.
therapy such as paromomycin could be attempted
12. Davis E, Rush BR, Cox J, et al.
Neonatal enterocolitis as-
but there are no ef?cacy data available for foals.
sociated with coronavirus infection in a foal:
a case report.
J Vet Diagn Invest 2000;12:153–156.
Prevention includes environmental disinfection and
13. Xiao L, Herd RP.
Epidemiology of equine Cryptosporidium
isolation of infected foals.
and Giardia infections.
Equine Vet J 1994;26:14 –17.
14. Netherwood T, Wood JL, Townsend HG, et al.
Foal diar-
Giardia
rhoea between 1991 and 1994 in the United Kingdom asso-
Giardia infection rates in foals have been reported
ciated with Clostridium perfringens, rotavirus, Strongyloides
westeri and Cryptosporidium spp.
Epidemiol Infect 1996;
to be as high as 35% but data associating shedding
117:375–383.
with disease are lacking.
There have been isolated
15. Cole DJ, Cohen ND, Snowden K, et al.
Prevalence of and
cases of suckling foals with diarrhea and high Giar-
risk factors for fecal shedding of Cryptosporidium parvum
dia counts who have responded to a short course of
oocysts in horses.
J Am Vet Med Assoc 1998;213:1296 –1302.
metronidazole.
a
3.
Conclusion
Becton Dickinson, Franklin Lakes, NJ 07417.
bBoehringer Ingelheim, Germany.
It is important to locate a laboratory that is capable
cVirogen Rotatest, Wampole Laboratories, Cranbury, NJ
of providing in-depth fecal analysis.
Most com-
08512; Rotazyme, Abbott Laboratories, Abbott Park, IL 60064.
AAEP PROCEEDINGS ? Vol. 47 ? 2001
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Proceedings of the Annual Convention of the AAEP 2001

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