Clostridium perfringens enterotoxicosis
Over the last 12 years Clostridium perfringens enterotoxicosis (CPE) has emerged as a frequently recognized cause of chronic intermittent diarrhea in dogs. Although it
is likely a less common cause of diarrhea in cats it is still diagnosed frequently enough that it should be considered in
the diagnosis of diarrhea in cats as well. This is not a new disease. Frequent use of the definitive test (enterotoxin assay
performed on feces) for this disorder has revealed that CPE is seen relatively commonly in clinical practice and that CPE
is a disorder that should be considered in any dog or cat with intermittent or chronic persistent diarrhea.
C. perfringens is a normal vegetative enteric organism. Simply identifying C. perfringens on a fecal culture is meaningless. The pathogenesis of CPE is through an enterotoxin that is produced after certain strains
of C. perfringens sporulate. The toxin damages epithelial cells of the distal ileum and colon. Inciting factors that promote sporulation are
not clearly understood but may include stress, diet changes, concurrent disease, or inherent immune status.
The most common clinical signs are chronic intermittent or persistent diarrhea. In some animals acute diarrhea is the primary
sign. In fact, some of the cases of hemorrhagic gastroenteritis (HGE syndrome), characterized by acute bloody diarrhea and
an increased packed cell volume that most practitioners have seen over the years, may have been due to CPE. Many animals exhibit
signs of large bowel diarrhea, but small bowel signs may be seen as well. In some cases signs may be seen for only a day or
two at a time, with persistent recurrences on a weekly, monthly, or on a less frequent basis. Stressful events or diet changes
may incite flare-ups of clinical signs. In other cases C. perfringens enterotoxicosis is one of several problems that an animal may have concurrently and diarrhea may be persistent.
CPE must be considered whenever more than one animal in the environment has diarrhea (e.g., household, kennel, cattery). Transmission
from animal to animal can occur. A presumptive diagnosis may be suggested on fecal cytology in which more than 3-4 spores
per high power oil immersion field are observed (the spores have a safety pin appearance and are larger than most bacteria).
However, definitive diagnosis is by identification of enterotoxin which is currently done via a fecal assay. Clinicians should
be aware that simply seeing spores on fecal cytology does not establish a definitive diagnosis (see JAVMA February 1, 1999).
Stool is submitted to the lab for enterotoxin analysis. Fecal samples that will be shipped off from the hospital directly
to a laboratory should be sent on ice via overnight express. If a courier service will be picking up samples for transport
to the laboratory it is sufficient to keep the sample refrigerated until pick-up. The courier service will keep the sample
properly chilled during transport. The minimum amount of stool that should be submitted is the size of a pea. Typically I
submit samples in a red top tube, without serum separator. In animals with intermittent diarrhea the chances of a positive
toxin finding are greater when abnormal rather than a normal stool is examined. A negative result does not definitively rule-out
Several antibacterial drugs are effective in controlling CPE. Acute cases often respond well to amoxicillin (22 mg/kg BID)
or metronidazole (10-20 mg/kg BID) for 7-28 days. Many clinicians have likely treated CPE with these medications empirically
without knowing what they were treating. Chronic cases tend to respond best to tylosin powder. The recommended dose is: Animals
greater than 23 kg 1/4 tsp BID, 12 to 23 kg 1/8 tsp BID, 5 to 12 kg 1/12 tsp BID, and less than 4.5 kg 1/16 tsp BID (a "pinch").
Cats definitely do not accept the powder well at all, even when it is mixed in very tasty foods. It is best to have the powder
reconstituted to capsule form for administration to cats. The medication is very safe. Some animals require treatment for
several to many months (3 to12 months or more). Over time the dose may in some cases be successfully reduced to SID and then
every other day dosage (after several months or more on a BID schedule).
Dietary fiber supplementation may also help control CPE. Probable mechanisms include decreased C. perfringens fecal concentration, lower colonic pH, which prevents sporulation, and increased concentrations of SCFA. Some patients may
respond well to dietary fiber supplementation alone.
Follow-up testing at 3-6 months can be done to determine if toxin persists. Once daily to every other day tylosin in conjunction
with dietary fiber supplementation are used in chronic cases.
Infection with Cryptosporidium is much more common than most small animal practitioners recognize. Currently it is recommended that all dogs and cats with
diarrhea, whether acute or chronic, be screened for Cryptosporidium in addition to testing for nematode and protozoan parasites. In 2004 the American Association of Feline Practitioners adopted
a position statement recommending that all kittens and adult cats with diarrhea be screened for Cryptosporidium. It is recommended that the same policy be followed with dogs (given that the cause is not simple diarrhea related to an
acute upset due to sudden change in diet or dietary sensitivity).
Cryptosporidium spp. are coccidians that reside in the gastrointestinal tract. Infection can be associated with diarrhea in both immunocompetent
and immunodeficient hosts. In the past, most of the cases of mammalian cryptosporidiosis were attributed to C. parvum. However, molecular studies have demonstrated that cats are usually infected with the host-specific C. felis, dogs are infected with C. canis, and people are infected with C. parvum or C. hominus (Scorza and Lappin). In a recent study at Colorado State University, they documented the presence of Cryptosporidium spp.
DNA in diarrhea from 24.3% of the 292 animals tested (180 cats, 112 dogs) (Scorza and Lappin). This highlights the importance
of testing dogs and cats for cryptosporidiosis. PCR is much more sensitive than the tests that are used most commonly at this
time (acid fast staining of fecal smears or IFA). In this same series with 24.3% positive on PCR, only 2.7% were positive
All dogs and cats infected with Giardia or Cryptosporidium species should be considered potentially zoonotic, even though the number of cases in which humans are infected through contact
with pets is probably not high. Infection in humans is sometimes fatal in the presence of severe immunosuppression. Acute
symptoms may include diarrhea, abdominal pain, vomiting, fever, and listless behavior. Infection can also be subclinical in
dogs and cats. Chronic unresponsive diarrhea has been associated with cryptosporidiosis in cats with serious underlying disease
as well as in dogs.
Because Cryptosporidia oocysts are quite small (as little as one-tenth the size of common Isospora oocysts) and are usually present in the feces in small numbers, they are very difficult to detect on routine fecal flotation
and microscopy. The best tests currently available for routine testing for Cryptosporidium are fecal IFA and acid fast staining of fecal smears; however, they lack sensitivity. These tests are readily available at
commercial laboratories (acid fast staining can also be done in house). PCR is a much more sensitive test but is labor intensive,
expensive and is only available at a limited number of laboratories. Antigen tests for detecting C. parvum in human species are not sensitive for use in dogs and cats. In time there will be more sensitive tests readily available.
The following treatment regimens may be used for cryptosporidiosis
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