Parasitic and infectious causes of vomiting and diarrhea in dogs and cats (Proceedings)


Physalloptera nematodes are an uncommon cause of chronic vomiting in dogs and uncommon to rare cause in cats. Since the ova are difficult to consistently find using fecal flotation the true importance is likely underestimated.


Physalloptera nematodes are an uncommon cause of chronic vomiting in dogs and uncommon to rare cause in cats. Since the ova are difficult to consistently find using fecal flotation the true importance is likely underestimated.  Diagnosis is made by routine fecal flotation or by seeing worms during gastroscopy.  Adults easily identified as 1-4 cm long nematode in fundus or antrum.  Larvae are small and easily overlooked.  The adults attach to the gastroduodenal mucosa.  They may cause small bleeding erosions and gastroenteritis.

The best treatment is unknown but any of the following therapies are probably effective:  pyrantel pamoate (Strongid® 5mg/kg PO once), fenbendazole (Panacur®  50 mg/kg PO q 24h for 3 days), ivermectin (200 mcg/kg PO or SQ q 14 d for 2 doses).  Because of the difficulty diagnosing this disease, empirical treatment prior to in-depth workup is recommended.  Re-infection is possible as Physalloptera requires an intermediate host.  Dogs and cats are infected by consuming beetles, cockroaches, crickets, frogs, snakes or mice that are affected.

 Ollulanus tricuspis is a gastric nematode of cats that is occasionally identified in dogs.  Its clinical significance is uncertain.  It is diagnosed by microscopic examination of vomitus for adult parasites.  Therapy is uncertain, but fenbendazole (10mg/kg q12h for 2 days) is effective in cats

.Helicobacter-associated gastritis is associated with spiral bacteria of the genus Helicobacter.  Helicobacter spp. infect the stomachs of many mammalian hosts, including humans, dogs, cats, ferrets and cheetahs.   Helicobacter pylori infection has been determined to be the primary cause of chronic gastritis and gastroduodenal ulcer disease in humans.  Gastric spiral bacteria are commonly found in the stomachs of dogs and cats, but in most cases infection is not clinically significant.  Helicobacter heilmannii and H. felis are the most common spiral bacteria found in dogs and cats and have been identified in clinically normal animals, as well as in those with clinical and histologic gastritis.

Because some dogs/cats infected with Helicobacter appear to develop gastritis whereas many others do not, the full pathogenic and clinical significance of infection is unclear.  Many reports of resolution of clinical disease following antimicrobial therapy exist; however, information is limited by lack of controlled study.  It is a good idea to treat a patient with clinical signs of gastritis and biopsy-confirmed Helicobacter-associated gastritis, when no other cause for the signs is identified.  In addition, H. heilmannii and H. felis may have zoonotic potential.  These organisms have been isolated from humans with chronic gastritis, most of whom have had close contact with dogs or cats. Additionally, H. pylori has been isolated from the stomach of dogs and cats, where it causes a low-grade gastritis.

Unfortunately, no protocol has been effective in treating all animals.  Although clinical signs may resolve after 3 weeks of therapy, eradication is rare.

Suggested protocols:

Amoxicillin + metronidazole + omeprazole  OR famotidine OR ranitidine

Amoxicillin + clarithromycin + omeprazole

Amoxicillin + metronidazole + bismuth subsalicylate

Clarithromycin + metronidazole + bismuth subsalicylate

Avoid bismuth in cats due to their innate salicylate sensitivity



Fecal testing

Collection and storage of feces  

Fresh fecal specimens (< 1 hr) should be examined whenever possible to maximize the likelihood of identifying a parasite. At least 5 g of feces should be placed in a clean, dry, airtight container. If samples cannot be examined immediately, they should be refrigerated (up to 1 week) to preserve the integrity of ova, oocysts and cysts.  Protozoal trophozoites must be examined in fresh feces that are not refrigerated. 

Fecal floatation    

Fecal floatations are indicated to find cysts, oocysts, and ova in feces. Although standing (gravitational) flotation methods are easier and quicker to perform than centrifugation flotation, the latter has clearly superior sensitivity. Animals with low parasite burdens could have a false negative result if the gravitational method is utilized. Solutions used in centrifugation flotation methods include zinc sulfate and Sheather's sugar.

Whipworms can be very difficult to diagnose and are best ruled out by evaluating 3 fecal samples and administering fenbendazole.  Occasionally, occult infections are diagnosed by seeing worms in the proximal colon or cecum during colonoscopy.  Since whipworms can be easily missed by fecal floatation, empirical treatment with fenbendazole is indicated in any dog with large bowel diarrhea. Although several monthly heartworm preventatives, such as Interceptor®, decrease the risk of clinical signs due to whipworms, they do not eliminate the risk. 


Infection with the ubiquitous protozoan parasites, Cryptosporidium parvum and C. felis, in puppies and kittens can cause a spectrum of disease ranging from asymptomatic carrier state to mild, transient diarrhea, chronic diarrhea or severe life-threatening malabsorption syndrome.  Although the organism can be found in clinically normal dogs, it is more likely to be shed in dogs and cats with diarrhea.  Animals < 1 year of age that are stray or in shelters are at the highest risk of shedding cysts in their feces.  The prevalence of infection has been documented as high as 12% in cats and is less frequent in dogs.  Cryptosporidium may also be found in dogs and cats infected with other intestinal parasites or in cats with FeLV or FIV infections.  Cryptosporidium is considered zoonotic.

Diagnosis with routine fecal evaluation is difficult.  The organism is small (average 4.6 × 4.0 μm) and difficult to find in fecal specimens via light microscopy.  Fecal shedding may also be intermittent. Immunofluorescent detection procedures are more sensitive and specific than acid-fast stains, and commonly used for diagnosis in humans.  Evaluating 3 fecal samples over 4 consecutive days by one of these techniques is up to 95% sensitive in detecting the organism.

In many affected animals treatment is unnecessary as infection is self-limiting.  Elimination of Cryptosporidium is difficult, and many effective drugs are toxic. Paromomycin administered at 125-165 mg/kg PO q 12 h for 5 days has been effective in some animals but has also been documented to cause acute renal failure.  Azithromycin administered at 7-10 mg/kg BID for 7 days is effective in people and but has not been evaluated in dogs and cats. 

Campylobacter spp. are small, curved rod-shaped bacteria.  Several species have been associated with canine enteric disease, with C. jejuni being the most commonly isolated. It is typically cultured from dogs and cats < 6 months of age, particularly from those housed in crowded, unsanitary environments.  Most infections are asymptomatic.  Clinically significant disease is usually restricted to young, parasitized, or immunocompromised animals.  Clinical signs include watery, mucoid, or hemorrhagic diarrhea accompanied by vomiting, tenesmus, pyrexia, and anorexia. Concurrent infection with Giardia, Salmonella, parvovirus, or coronavirus causes more severe disease.

Campylobacter organisms were isolated from 36 of the 122 (30 %) cats that were < 1 year old but from only 1 of the 30 (3 %) cats > than 1 year old.  Shedding was more common during the summer and fall months. No association between Campylobacter shedding and clinical signs of disease was identified.

Diagnosis is best made by culture of fresh feces. The presence of slender, seagull-shaped bacteria on a stained fecal smear yields a presumptive diagnosis. Treatment is indicated in animals with severe hemorrhagic mucoid diarrhea.  Erythromycin or fluoroquinolones are suggested.  Resistance to antibiotics has been reported, and post-treatment cultures should be performed to document eradication.  It is important that the owner be instructed in hygienic precautions to prevent zoonotic infection.

Salmonella spp. are gram-negative motile rods that invade the intestinal epithelium, especially the distal ileum and colon. Asymptomatic carriers are common.  Salmonella has been isolated from the feces of up to 30% of healthy dogs and 18% of healthy cats. Salmonella spp can cause acute, hemorrhagic gastroenteritis associated with systemic signs, including fever, neutropenia and signs of sepsis.  Endotoxemia, DIC and death can occur.  Small, large, or mixed diarrhea may be present. Clinically significant disease is unusual and occurs most frequently in young, parasitized, kenneled, or immunocompromised animals.  About 50% of cats, however, present with fever and no GI signs.  In cats, salmonellosis may be associated with recent ingestion of a song bird (S. typhimurium). 

Diagnosis is based on the isolation of Salmonella from feces or from blood in septic patients.  Antibiotic treatment may promote bacterial resistance and a carrier state and is not recommended when Salmonella is isolated from healthy infected animals or stable animals with acute diarrhea.  In animals with severe hemorrhagic diarrhea, marked depression, shock, persistent pyrexia, or sepsis, parenteral antibiotics should be given. The choice of antibiotic should be based on sensitivity testing when possible, but fluoroquinolones are frequently effective.  Therapy initially should be given for 10 days, but prolonged therapy may be required. The feces should be recultured on several occasions to ensure that the infection has been eliminated:  it is very important to prevent the development of resistance.


The prognosis for diarrhea associated with salmonellosis is usually good. A guarded prognosis should be given in patients with septicemia. Negative prognostic indicators include peracute onset, marked pyrexia, hypothermia, severe hemorrhagic diarrhea, degenerative left shift, and hypoglycemia. Inform owners of a zoonotic potential.  Almost all Salmonella spp. Infect both people and animals and dogs and cats can be vectors

Histiocytic ulcerative colitis is an uncommon to rare disease, predominantly diagnosed in boxers.  It is due to infection with enteropathogenic E. coli.  It has been diagnosed in French bulldogs, a mastiff, Siberian Husky, Doberman pincher and a cat.  It is associated with an onset of severe large bowel diarrhea in young dogs, typically < 6 months of age.  Hematochezia can be severe.  Many dogs defecate > 10 times daily.  Anorexia, weight loss and death usually occur if untreated.  Treatment is with 8 weeks of enrofloxacin.  If administered for a shorter period of time, antibiotic resistant may develop and increase risk of death.

Histoplasma capsulatum is a dimorphic fungus.. It typically causes subclinical respiratory infection after inhalation of the organism.  If dissemination occurs, infection of the small and large bowel is the most common form of the disease in dogs.  In cats, intestinal infection is rare, whereas cutaneous involvement is more common. Infiltration of H. capsulatum into the bowel wall results in severe granulomatous inflammation that disrupts digestive and absorptive function. 

Clinical signs frequently include chronic, mixed- bowel diarrhea, severe weight loss, and anemia are common, although large bowel diarrhea often predominates.  Malabsorption and protein-losing enteropathy can contribute to formation of ascites.  Lethargy, fever, anorexia, dyspnea, and jaundice are frequently observed.  Physical examination usually reveals an emaciated animal with mesenteric or peripheral lymphadenopathy, hepatosplenomegaly, intestinal, or colonic thickening.

Diagnosis is by finding the organism in cytologic or histopathologic samples.  Colonic mucosal scrapings, fine-needle aspirate of enlarged lymph nodes, liver, spleen or lungs, or bone marrow aspirates usually reveals organisms within macrophages. 

Routine laboratory evaluation is non-specific but may show a non-regenerative anemia, leukocytosis, thrombocytopenia, hyperglobulinemia and hypoalbuminemia.  Serologic testing is not a reliable diagnostic test because of lack of specificity and sensitivity. In cases where infection is suspected, but can't be proven, assessment for the antigen in urine and serum samples can be performed.  Although these tests need to be validated in dogs and cats, results are promising.  If cytology is non-diagnostic, biopsy of affected tissue is required.

Treatment is with itraconazole at a dose of 5mg/kg PO q 12 h for 60-90 days (or until the clinical illness has been resolved for at least 1 month).  If severe intestinal disease is present, absorption of itraconazole may be impaired.  In these cases administration of amphotericin B intravenously (0.5mg/kg PO three days per week for 4-6 treatments, or until azotemia develops), followed by long-term itraconazole is recommended. Prognosis is fair to poor, depending on extent of disease.


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