Chronic vomiting is a common gastrointestinal complaint in dogs and cats, and is often linked to chronic gastritis; spiral bacteria have been suggested as one etiologic factor for chronic gastritis (Guilford and Strombeck 1996). Spiral-shaped microorganisms were observed originally as early as the end of the 19th century within the stomachs of animals (Rappin 1881). Rappin (1881) found helicobacters in the gastric mucosa of a dog, and his work was confirmed by Bizzozero (1893) and Salomon (1896) in dogs, cats, and rats. These bacteria were first named Spirillum (Rappin 1881) or Spirochete (Lockard and Boler 1970), then they were classified Campylobacter, and now they belong to the genus Helicobacter (Owen 1998). At least four Helicobacter species may colonize the canine and feline stomach: Helicobacter felis (Lee et al 1988, Paster et al 1991), Helicobacter bizzozeronii (Hänninen et al 1996), Helicobacter salomonis (Jalava et al 1997), and "Flexispira rappini" (also called "Helicobacter rappini") (Lockard and Boler 1970, Eaton et al 1996, Jalava et al 1998). Mixed infections are common in dogs and cats (Lockard and Boler 1970, Lee et al 1988). What has not been clarified is whether any one Helicobacter species is more pathogenic than another, or whether a mixed infection differs from that of one species. Dogs are not found to be naturally colonized with human Helicobacter pylori (formerly Campylobacter pylori). However, H. pylori has been shown to colonize gnotobiotic dogs in an experimental infection model (Radin et al 1990). One study reports H. pylori in commercial vendor cats (Handt et al 1994). "Helicobacter heilmannii" (formerly "Gastrospirillum hominis"), the second species detected in humans in a minority of cases (McNulty et al 1989a, Solnick et al 1993, Andersen et al 1996 & 1999), resembles by morphology H. bizzozeronii, and it has been speculated whether these are one and the same species. A recent detailed comparative analysis of a human isolate of other helicobacters revealed that the cultured human "H. heilmannii" strain examined (Andersen et al 1999) was in all characteristics identical to H. bizzozeronii (Jalava et al 1999a). An interesting suggestion has also been made that some reports of "H. heilmannii" may represent in vivo growth of H. pylori based on different morphology of the single strain of bacteria when it was grown on blood agar plates or in broth cultures (Fawcett et al 1999).
The genus of Helicobacter includes at least 18 formally described species and several novel species that have not been validly named (Fox and Lee 1997, Owen 1998, Wadström and Hänninen 1999). Several Heliocbacter species have been described from gastric mucosa also of other animals than the dog and cat, including Helicobacter mustelae in ferrets, "Gastrospirillum suis" in pigs, Helicobacter nemestrinae in monkeys, and Helicobacter acinonyx (acinonychis) in cheetahs (Fox and Lee 1997). In addition to the gastric mucosa, helicobacters have been isolated from the intestine and liver, such as Helicobacter canis from the intestine and liver of dogs (Stanley et al 1993, Fox et al 1996a), Helicobacter cinaedi from the intestine of humans and hamsters (Totten et al 1985, Gebhard et al 1989), Helicobacter muridarum and Helicobacter rodentium from the intestine of mice (Lee et al 1992a, Shen et al 1997), Helicobacter trogontum from the intestine of rats (Mendes et al 1996), Helicobacter pametensis from the intestine of birds and swine (Dewhirst et al 1994), Helicobacter pullorum from the intestine and liver of poultry and from the intestine of humans (Stanley et al 1994), Helicobacter bilis from the liver and intestine of mice (Fox et al 1995), Helicobacter hepaticus from the liver of mice (Fox et al 1994), and Helicobacter cholecystus from the liver of hamsters (Franklin et al 1996).
Human H. pylori has been studied keenly for the past 15 years since its culture from man in 1982 and the discovery that it may cause gastritis (Warren 1983, Marshall 1983). Later, it was demonstrated that H. pylori plays an important role in the etiology of human dyspepsia, gastritis, and gastroduodenal ulceration (Marshall and Warren 1984, Goodwin et al 1986, Graham 1989, Sipponen et al 1993), and is a risk factor for gastric carcinoma and lymphoma (Parsonnet et al 1991, Sipponen et al 1992). Interest in canine and feline gastric helicobacters began to increase a few years ago when the strong association of H. pylori in man with gastric diseases became evident and universally accepted, and at present, these bacteria are under intensive study.
Colonization of the gastric mucosa of dogs and cats with large spiral helicobacters is common (Weber et al 1958, Henry et al 1987, Geyer et al 1993, Hermanns et al 1995, Eaton et al 1996, Yamasaki et al 1998). In cats, helicobacters have been found more often in adult than in juvenile cats (Weber et al 1958, Otto et al 1994), but in dogs this association is unknown. The true prevalence of gastric helicobacters among pet dogs and cats has remained unclear because previous studies either have been performed on laboratory animals (Weber et al 1958, Henry et al 1987), or the clinical background of the pet dogs has been obscure (Geyer et al 1993, Hermanns et al 1995, Yamasaki et al 1998). The route of transmission of gastric helicobacter in animals is also unknown. Human H. pylori is suspected to be transmitted in early life by oral-oral contact (Taylor and Blaser 1991), although the fecal-oral route is also suggested (Kelly et al 1994). Close personal contact seems to be an important factor in transmission of H. pylori. Dogs usually live in close social contact with each other; dams and puppies are especially in close contact during the lactation period. Dogs can therefore serve as an animal model for studying the transmission of gastric helicobacters during the early weeks of life.
Diagnosis of H. pylori infection in man can established by brush cytology, the urease test, histologic examination, electron microscopy, culture, serology, the urea breath test, and molecular methods (de Boer 1997). Of these methods, histologic examination, the urease test, and electron microscopy have been used most commonly for detecting helicobacters in animals. Comparisons between diagnostic methods for human H. pylori have been performed and reviewed from various angles (Chodos et al 1988, Brown and Peura 1993, Cutler et al 1995, de Boer et al 1997, Cutler 1997, Onders 1997), but the superiority of any one method has not been evaluated in animals.
It has been assumed that canine and feline helicobacters may be responsible for histologic changes seen in the stomach in conjunction with these organisms. However, such changes have been detected both in dogs and cats with upper gastrointestinal signs and in clinically healthy dogs and cats (Weber et al 1958, Henry et al 1987, Lee et al 1992b, Geyer et al 1993, Otto et al 1994, Hermanns et al 1995, Yamasaki et al 1998). Some of these conclusions have been drawn from studies on experimentally induced helicobacter infections (Lee et al 1992b). That the histologic definition of gastritis of dogs and cats has varied from study to study has made comparison of results very difficult. Thus far, no study has given an unambiguous answer to the question whether canine and feline helicobacters are of clinical importance. Gastric helicobacters differing from canine and feline ones have been associated with variable degrees of histologically verified gastritis in their hosts, e.g., H. mustelae in ferrets (Fox et al 1986 & 1990), "G. suis" in pigs (Mendes et al 1990), H. nemestrinae in monkeys (Bronsdon et al 1991), and H. acinonyx (acinonychis) in cheetahs (Eaton et al 1993).
In humans, eradication of H. pylori is more effective in preventing recurrence of gastroduodenal ulcers than is traditional treatment with acid blockers, and reinfection with H. pylori is rare after successful eradication (Seppälä et al 1992, Labenz and Börsc 1994, Uemura et al 1995). The present recommendation for H. pylori eradication therapy consists of amoxicillin or tetracycline with metronidazole, plus omeprazole or bismuth subcitrate (European Helicobacter Pylori Study Group 1997). Only a few preliminary reports have been published on eradication therapy for canine and feline gastric helicobacters (Lecoindre et al 1998) and none on its effect on gastrointestinal signs or gastric histology.