Gastric Helicobacter spp. and Chronic Vomiting in Dogs

Chapter 124


Gastric Helicobacter spp. and Chronic Vomiting in Dogs



Spiral bacteria were identified in the stomachs of humans and animals in the late 1800s. However, it was not until the early 1980s that Warren and Marshall proposed a relationship between Helicobacter pylori and gastric disease in humans. Soon after, studies demonstrated that spiral bacteria were common in the stomachs of clinically normal dogs and cats, as well as those with signs of gastrointestinal (GI) disease. Experimental infection in dogs and cats resulted in lymphoid follicular gastritis; however, clinical signs were absent or very mild.


Currently a direct causal relationship between spiral bacteria and chronic gastritis and vomiting or with gastric neoplasia has not been established firmly in dogs or cats. However, based on clinical experience and several clinical studies evaluating dogs and cats treated for Helicobacter spp. and identifying improvement or resolution of clinical signs, the author believes that gastric Helicobacter spp. can cause or contribute to the clinical signs in some dogs and cats with chronic gastritis and vomiting (Happonen et al, 2000; Jergens et al, 2009; Leib et al, 2007). In addition, a potential relationship between gastric lymphoblastic lymphoma and Helicobacter heilmannii in cats has been proposed (Bridgeford et al, 2008).


The author routinely determines whether gastric Helicobacter spp. are present in all dogs and cats with chronic vomiting that undergo upper GI endoscopy in his clinic. In most instances, dogs and cats with gastric Helicobacter spp. and gastritis, with and without inflammatory bowel disease (IBD), are treated initially for Helicobacter spp. If clinical signs continue, dietary or antiinflammatory therapies for gastritis and IBD are instituted. Although the potential pathogenic role of gastric Helicobacter spp. in dogs and cats is being investigated, a thorough diagnostic evaluation to search for other potential causes of chronic vomiting always should be performed before considering Helicobacter spp. to be the primary etiologic agent. The purpose of this chapter is to describe the commonly used methods of identifying gastric spiral bacteria in dogs and cats and to review the evidence behind current treatment recommendations. Recommendations for humans with H. pylori have been modified by the results of hundreds of clinical studies. Treatment recommendations in dogs and cats no doubt also will change as further studies are performed.



Pathogenesis


Helicobacter spp. are gram-negative, microaerophilic, motile, curved-to-spiral bacteria with multiple terminal flagella. They contain large quantities of the enzyme urease, which results in the production of ammonia and bicarbonate when in contact with urea that is present in gastric juice. This reaction alters the pH immediately surrounding the bacteria and helps them colonize the acidic environment of the stomach.


More than 35 Helicobacter spp. have been identified in humans and animals. At least seven species have been identified in the stomachs of dogs and cats. In addition to the gastric species, others also have been identified in the intestine and liver. H. pylori is the most common gastric species in humans. H. pylori has been shown to be a major cause of gastritis and peptic ulcers and to increase the risk of gastric cancer. Infection rates can approach 100% in developing countries and 25% to 60% in developed countries. Infection usually is acquired in childhood and most often persists for life; natural immunity does not clear the infection. Most infected humans remain asymptomatic, but peptic ulcers may occur in approximately 16% of those infected, whereas gastric cancer may develop in 1% to 2% of infected humans. Symptomatic disease usually takes decades to develop in humans. Development of clinical signs is related to bacterial virulence, environmental factors, and host genetics, especially relating to the cytokine response to infection. Eradication of H. pylori usually results in healing of gastric and duodenal ulcers and remission of low-grade gastric mucosa–associated lymphoid tissue (MALT) lymphoma.


Although H. pylori has been identified in a research colony of cats, infections in pet dogs and cats with other species of Helicobacter is more common. Gastric Helicobacter spp. usually found in dogs and cats are larger than H. pylori (1.5 to 3 µm). Initially these large spiral bacteria (4 to 10 µm) were called Gastrospirillum hominis but were later reclassified as Helicobacter heilmannii. Other large gastric spiral bacteria such as Helicobacter felis, Helicobacter bizzozeronii, and Helicobacter salomonis are found and are indistinguishable from H. heilmannii using routine light microscopy. Multiple species also can be present within an individual animal. Gastric or duodenal ulceration associated with Helicobacter spp. is rare in dogs and cats, demonstrating a major pathophysiologic difference between H. pylori and the gastric spiral bacteria commonly found in dogs and cats. In addition to the role of Helicobacter spp. in the pathogenesis of gastritis and chronic vomiting in dogs and cats is the potential for zoonotic transmission. Most evidence indicates zoonotic transmission to be very low, but the potential is real. H. heilmannii is a rare cause of gastritis in humans, accounting for approximately 0.1% of cases. An epidemiologic survey of humans with H. heilmannii gastritis showed that contact with dogs and cats was a significant risk factor (Meining et al, 1998). In addition, there was an association between H. heilmannii gastritis and gastric lymphoma, although this relationship could be coincidental (Stolte et al, 1997). Some studies have identified cat ownership as a risk factor for H. pylori infection in humans, whereas others have found contact with dogs or cats not to be a risk factor for H. pylori infection. Although the potential for zoonotic transmission appears slight, until this issue is resolved conclusively, it seems prudent to identify the presence of gastric Helicobacter spp. in dogs and cats during the diagnostic evaluation of chronic vomiting.



Diagnostic Tests


Invasive methods of diagnosis of gastric Helicobacter infection in humans include bacterial culture, routine microscopic or ultrastructural examination, polymerase chain reaction, or rapid urease testing of gastric mucosal biopsy specimens, usually obtained via endoscopy. Noninvasive methods of diagnosis include urea breath testing, fecal antigen determination, and serology. Although many of these noninvasive tests have been investigated in dogs and cats, they are not routinely available. Presently the clinical diagnosis of gastric Helicobacter spp. in dogs and cats requires endoscopic examination or exploratory celiotomy for retrieval of gastric biopsy samples. Recently, gastric washing with saline has identified spiral bacteria in a small group of cats. In the author’s clinic, spiral bacteria are identified on gastric biopsy, from gastric brush cytology specimens, or indirectly by a positive rapid urease test using a gastric mucosal sample. Results from a rapid urease test and gastric brush cytology are available much sooner than results from histopathology. For reasons discussed in the following paragraphs, gastric brush cytology and histologic evaluation of biopsy samples are considered to be the most practical diagnostic tests available to the practicing veterinarian.



Brush Cytology


Gastric brush cytology is the least expensive and most practical diagnostic method with the quickest turnaround time. After completion of an endoscopic examination and collection of biopsy samples from the duodenum and stomach, a brush cytology specimen is collected. A guarded cytology brush is passed through the biopsy channel of the endoscope into the gastric body along the greater curvature. The cytology brush is extended from the sheath and gently rubbed along the mucosa from the antrum toward the fundus, along the greater curvature. Hemorrhagic areas associated with previous biopsy sites should be avoided. The brush is retracted into the protective sheath and withdrawn from the endoscope. The brush is extended from the sheath, gently rubbed across several glass microscope slides, which are air dried, and stained with a rapid Wright stain (Dip Quick stain). The slide is examined under 100× oil immersion. Areas with numerous epithelial cells and large amounts of mucus are examined initially for Helicobacter spp. If present, the spiral bacteria are seen easily. They are usually at least as long as the diameter of a red blood cell, and their classic spiral shape is obvious (Figure 124-1). The number of spiral bacteria can be highly variable, from one every several fields to massive numbers in most fields. At least 10 oil immersion fields are examined on two slides before the specimen is considered negative. Unlike diagnostic tests that involve using a single or several small biopsy samples, brush cytology gathers surface mucus and epithelial cells from a much larger area, increasing the chances for identification of bacteria. Brush cytology was found to be more sensitive than urease testing or histopathologic examination of gastric tissues in identifying Helicobacter spp. organisms in dogs and cats (Happonen et al, 1996).


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Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Gastric Helicobacter spp. and Chronic Vomiting in Dogs

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