Campylobacter jejuni hepatitis in a horse: case report and literature review

Campylobacter sp. is a gram-negative, motile, curved rod that is a fastidious grower and usually requires microaerophilic conditions for growth. ¹ The Campylobacter spp. include a diverse group of organisms, some of which can cause clinical illness in humans and other animals. Reports of gastrointestinal diseases in horses caused by Campylobacter spp. are limited.^{1,4 –6,8,15} We retrieved cases of Campylobacter jejuni causing hepatitis in horses in a search of Google, PubMed, CAB Direct, Web of Science, and Scopus, using the search terms: “Campylobacter jejuni”, “horses”, and “hepatitis”. Here we present a case of hepatitis caused by C. jejuni in a 3-y-old gelding, and we also review the literature on hepatic disease caused by Campylobacter spp. in various animal species.

In mid-November 2023, a 3-y-old, crossbred gelding at a dressage training facility lost weight, and became weak and recumbent over 1 wk before dying. The horse was submitted for autopsy to the Tulare branch of the California Animal Health and Food Safety Laboratory System, University of California–Davis (CAHFS-UCD; Tulare, CA, USA). Postmortem examination was performed ~8 h after death. The carcass was in fair nutritional condition, with minimal fat and mildly atrophic musculature. Postmortem decomposition was mild based on the gross and microscopic appearance of tissues. A small amount of pink stable foam was in the lumen of the trachea and lower airways. The liver was pale and swollen, had rounded edges, and many 0.5–3.5-cm red-to-brown foci and ~2.5-cm, blotchy pale-tan areas on the surface (Fig. 1). On section, similar random mottling was noted, and the edges of the cross-sections bulged slightly (Fig. 2). The stomach was empty, and the serosa had many 0.5–1.5-cm dark-red, well-demarcated foci. Throughout the small intestine and the large colon was a large amount of mucoid pale-green-to-yellow content that occasionally adhered to the mucosa.

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Figures 1–4.

Gross and microscopic findings in Campylobacter jejuni–associated hepatitis in a horse. Figure 1. The liver is pale and swollen, and has rounded edges, numerous red-to-brown foci, and blotchy pale-tan areas. Figure 2. On section, the liver is mottled with pale and darker areas intercalated. Figure 3. In a focally extensive area of necrosis and neutrophilic infiltration, there are small numbers of lymphocytes and plasma cells within the sinusoids and in the portal areas. Inset: higher magnification of neutrophilic infiltrate. H&E. Figure 4. The portal areas have neutrophilic cholangitis, bile duct hyperplasia, and fibrosis. H&E.

Samples of liver, lung, kidney, spleen, skeletal muscle, adrenal gland, small intestine, stomach, colon, and brain were collected, fixed in 10% neutral-buffered (pH 7.2) formalin for ~24 h, and processed routinely for the production of 4.0-µm thick H&E sections. Additional sections of kidney and liver were also stained with Steiner and Gram stains, and additional sections of kidney were processed by Masson trichrome and immunohistochemistry (IHC) for Leptospira spp.

Microscopically, random areas of neutrophilic inflammation were associated with hepatocellular necrosis (Fig. 3). Other changes in the liver included mild neutrophilic cholangitis, moderate bile duct hyperplasia, occasional portal edema, cholestasis, mild portal fibrosis, and lymphoplasmacytic infiltrates (Fig. 4). The mucosa, and occasionally the submucosa, of the small intestine and colon was infiltrated by large numbers of lymphocytes and plasma cells, and there was occasional crypt necrosis. In the kidneys, there was mild global thickening of the glomerular basement membranes by fibrous tissue, which stained positively with Masson trichrome. The proximal and distal tubular epithelium was eroded, and a scant amount of eosinophilic homogeneous fluid was occasionally mixed with neutrophils, lymphocytes, and karyorrhectic debris in the lumen; there was also multifocal interstitial hemorrhage. No microorganisms were observed in sections of liver or kidney stained with Steiner or Gram stains. IHC for Leptospira spp. on kidney sections was negative.

Samples of liver were collected aseptically and inoculated onto Columbia agar with 5% sheep blood (Hardy) and MacConkey (MAC) agar plates (Hardy), and incubated in 7% CO₂ at 37°C for 48 h. Small numbers of mucoid, white, non-hemolytic colonies in pure culture were seen on the Columbia agar at 48 h. The isolated organism was oxidase- and catalase-positive, gram-negative, curved to gull-wing shaped, and identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS; Bruker) as C. jejuni (score 2.2); further distinction for subspecies was not done. Salmonella sp. PCR of liver performed on tetrathionate enrichment broth (Vet Med Biological Media Services, UCD) culture and incubated for 18–20 h at 37°C was negative.

A diagnosis of necrosuppurative hepatitis caused by C. jejuni was established based on the gross and microscopic lesions coupled with the isolation of a pure culture of this microorganism from the liver. The source of exposure to C. jejuni was not determined. A small percentage of healthy horses can shed C. jejuni in feces, ¹³ and thus can contaminate feed and water, which were considered as a source; unfortunately, samples from these specimens were not available for culture.

In one study, C. jejuni was detected by PCR in 6 of 23 fecal samples from healthy horses, ¹⁴ along with Salmonella enterica serovar Typhimurium (5 of 23) and Enterococcus faecalis (14 of 23). In another report, C. fetus subspecies fetus was isolated from a fresh fecal sample of a horse with chronic diarrhea. ⁶ This subspecies of Campylobacter was also isolated from an abdominal abscess in a 12-y-old Warmblood mare. ¹⁵

In our case, based on the pattern of lesions, we hypothesize that C. jejuni reached the liver from the intestine via the portal vein and/or the biliary tree. The acute suppurative cholangitis observed suggests that the bacterial infection also involved the biliary tree. There were large lymphoplasmacytic infiltrates in the mucosa and occasionally the submucosa of the small intestine and colon, along with scattered areas of crypt necrosis, which might have been caused by C. jejuni. It is not clear if the pathogen was present in the intestine initially and invaded the liver ascending via the biliary tree or if it reached the liver by blood and spilled into the biliary tree. Because neither blood nor intestinal content was cultured for Campylobacter, this remains speculative. The bile duct hyperplasia, portal fibrosis, and lymphoplasmacytic infiltrate observed are nonspecific and were most likely not related to the infection by C. jejuni. Toxic substances such as pyrrolizidine alkaloids can cause portal fibrosis, and the lesions in our case may have been produced by these alkaloids; however, we were not able to confirm this speculation.

Campylobacter spp. can be found in the gastrointestinal tract of many healthy animals including mammals and birds. Wild birds can carry this microorganism and contaminate the environment of grazing herbivores. ⁴ In animals, C. fetus and C. jejuni are the 2 most significant Campylobacter spp. ¹⁸ A not-yet-identified species of Campylobacter has been associated with necrotizing hepatitis in chickens.^2,7 There are 2 subspecies of C. fetus, namely subspecies fetus and subspecies venerealis. ²⁰ These 2 subspecies are well-known causes of reproductive failure in ruminants, ²⁰ and their distinction is key, as they can cause different syndromes. There are 2 subspecies of C. jejuni, namely subspecies jejuni and subspecies doylei, the latter being primarily isolated from human clinical samples. ⁴ C. jejuni subsp. jejuni may produce disease depending on the immune status of the host, and several bacterial virulence factors. Infection of humans and other animals with C. jejuni subsp. jejuni occurs via the fecal–oral route by ingestion of contaminated food or water. ⁴ C. jejuni subsp. jejuni and Campylobacter coli are the 2 most common causes of bacterial foodborne gastroenteritis in humans. ¹⁸ In our case, the subspecies was not determined at the time of isolation, and the isolate was lost during subsequent flooding of the laboratory.

C. jejuni subsp. jejuni, C. coli, C. upsaliensis, and C. helveticus can cause intestinal disease in dogs, cats, and goats. Pigs carry C. coli and C. jejuni subsp. jejuni as part of their normal intestinal flora, and they excrete the organism in their feces. However, these microorganisms do not cause hepatitis in pigs. ¹⁹ The role of pigs in the epidemiology of infections by C. coli and C. jejuni subsp. jejuni is mostly associated with contamination of pork meat at slaughter with antimicrobial-resistant strains. ¹⁹

Avian species have a high rate of colonization and frequently carry C. jejuni subsp. jejuni at a higher prevalence than other animal species. Although C. jejuni has been suggested to produce hepatitis in chickens, the role of this pathogen in this lesion has not been confirmed. In a study evaluating livers of commercial broiler chickens at slaughter, Campylobacter sp. was isolated in both normal livers and those with focal hepatitis. However, livers with hepatitis had significantly more Campylobacter spp. than those with no lesions. The researchers were not able to replicate the disease in healthy hosts following experimental infection with C. jejuni. ⁷ Such results suggest that Campylobacter spp. alone are not sufficient to cause hepatitis in chickens. Campylobacter hepaticus has been proposed as the cause of spotty liver disease in laying hens. Although its zoonotic potential is not known, this microorganism is closely related to the known zoonotic agents C. jejuni and C. coli, ² suggesting that this microorganism may also be a zoonotic agent.

Hepatitis was induced experimentally in Japanese quail inoculated in the pancreatic duodenal vein with 2 C. jejuni strains originating from chicken hepatitis and human diarrhea cases, respectively. ¹¹ Although no clinical signs were observed in quail, IHC detected bacterial antigens in the hepatocytes, intercellular spaces, and in the macrophages during early stages of infection. The bacteria also invaded the bile and was retained in the gallbladder for a long period.

Fetal infection in ruminants requires C. jejuni to translocate from the intestinal tract of the dam into the blood and then pass through the placenta to the fetus. Hepatitis due to Campylobacter spp. in adult animals is not reported commonly, but C. jejuni has been isolated from the gall bladder of adult ruminants, ¹⁸ and both C. fetus subsp. fetus and C. jejuni are natural inhabitants of the intestinal tract and gallbladder of healthy ruminants. ¹⁸ C. jejuni and C. coli have been detected by PCR and isolated in bacterial culture of gallbladder samples of sheep slaughtered at abattoirs, ³ but no macroscopic nor microscopic lesions were recorded in the examined gallbladders or livers of those animals. In one paper, approximately one-third of ovine and caprine fetuses that had aborted due to C. jejuni subsp. jejuni had necrotizing hepatitis. ¹²

Clinical presentations of C. jejuni infections in humans include mainly bacteremia, cholecystitis, and pancreatitis. ¹⁰ In humans, bacteremia seems to be the least frequent of the clinical manifestations, but blood cultures are obtained infrequently in patients with enteritis. Hepatitis due to Campylobacter spp. in humans could be underdiagnosed because few studies involving enteritis have reported the results of liver function tests. ¹⁰ Campylobacter hepatitis in animals is rare, and the pathogenesis of the lesion is due to direct invasion of the parenchyma by the organism or to structural and functional changes caused by circulating toxins. ⁹

Diagnosis of Campylobacter hepatitis in humans is frequently established by ruling out other cases of hepatitis. ¹⁰ Hepatitis secondary to acute gastroenteritis due to Campylobacter spp. with or without sepsis is rarely described in humans and animals.^16,17 Hepatitis due to Campylobacter spp. can be underdiagnosed in acute cases, and liver enzyme activities along with microaerophilic cultures of liver should be performed in cases of gastrointestinal diseases in young and adult horses.