AEROBIC/MICRO-AEROPHILIC, MOTILE, HELICAL/VIBROID GRAM-NEGATIVE BACTERIA

A General Introduction has been added to each disease chapter in an attempt to give a brief updated overview of the taxonomic, biological and other characteristics of the virus family or group of bacteria /protozoa that cause disease in livestock and, where relevant, involve wildlife. As the text of the three-volume book Infectious Diseases of Livestock is currently under revision the Editors are aware that there are inconsistencies between the updated introductions to chapters and the content of the chapters themselves. Once the chapters have been updated – a process that is currently underway – these inconsistencies will be removed.

This group of bacteria is mostly classified in the epsilon subdivision of the Proteobacteria with bacteria of veterinary importance belonging to the Campylobacter group that consists of the genera Campylobacter and Arcobacter, and the Helicobacter group.^{5, 10} An exception is Lawsonia, which falls in the delta subdivision of the Proteobacteria. These bacteria are characterized by having helical or vibroid cell forms that may have less than one too many complete helical turns. They are all motile by virtue of the action of their polar flagella moving in straight lines with a characteristic corkscrew- like motion.

Although there are several genera within this group, only the genera Campylobacter, Arcobacter, Helicobacter and Lawsonia are of veterinary importance. These bacteria are usually found in the gastrointestinal and reproductive tracts.

Campylobacter fetus subsp. venerealis, a cause of an infertility syndrome in cattle known as bovine genital campylobacteriosis, and C. fetus subsp. fetus, which is found in the intestinal tract, can cause abortions in domestic ruminants (Table 1). The thermophilic campylobacters, C. jejuni subsp. jejuni and C. coli, are associated with diarrhoea in animals and can be transmitted to humans via the ingestion of faecally contaminated meat or other material.

Helicobacter spp. are found either in the stomach or intestinal tract of animals. The type species is associated with gastritis, gastric ulcers and squamous cell carcinoma of the stomach in humans. In animals several Helicobacter species have been isolated from the stomach but their association with disease has not been clarified for all the species. Helicobacter acinonychis and H. bizzozeroni have been associated with gastritis in cheetah (Acinonyx jabatus) and domestic dogs respectively.^{1, 3}

Species of the aerotolerant Arcobacter that are associated with abortions and enteritis in cattle and pigs are A. skirrowii, A. butzleri and A. cryaerophilus.^{10, 11} Arcobacter butzleri and A. cryaerophilus have been isolated from humans suffering from bacteraemia, endocarditis, peritonitis and diarrhoea.⁴

Lawsonia intracellularis, the only species in the genus Lawsonia, is an obligate intracellular pathogen affecting cells of the ileum in pigs and is associated with the porcine intestinal adematosis complex (which includes four different enteropathic syndromes).⁶

Lawsonia intracellularis or a L. intracellularis-like organism has also been associated with a similar disease in weaned three- to seven-month-old foals, known as ‘equine proliferative enteropathy’.^{2, 11, 12} These foals are lethargic, become emaciated and are hypoproteinaemic. Diarrhoea may be absent, mild, or profuse, watery and chronic.^{2, 7, 11} Signs of colic and oedema of the ventral aspects of the body and conjunctivae have also been reported in some affected foals.^{2, 7} On histopathology a multifocal hyperplasia of the intestinal crypt epithelium with primarily a lymphocytic in flammatory response was noted especially in the ileum and distal jejunum,^{2, 7, 11} but, in some, it may involve the entire small intestine. Although the disease has proved to be fatal in most of the reported cases, the combination of side-to-side anastomosis between the mid-portion of the jejunum proximal to visible lesions to the caecum together with parental erythromycin therapy resulted in full recovery of a foal.⁷ In one outbreak treatment of affected foals on a farm with parenterally administered erythromycin for two to three weeks resulted in clinical improvement.⁷

Other bacteria that are similar in morphology but are currently unclassified⁵ and do not belong to the genus Spirillum, are ‘Spirillum’ minus, the cause of a form of rat-bite fever in humans and monkeys known as Soduku,⁹ and ‘Spirullum’ pulli that is associated with diphtheroid stomatitis in chickens.

Table 1 Common pathogenic Campylobacter species that cause disease in livestock

References

1. EATON, K.A., DEWHIRST, F.E., RADIN, M.J., FOX, J.G., PASTER, B.J., KRAKOWKA, S. & MORGAN, D.R., 1993. Helicobacter acinonyx sp. nov., isolated from cheetahs with gastritis. International Journal of Systemic Bacteriology, 43, 99–106.
2. BEES, D.J., SONDHOFF, A.H., KLUGE, J.P., ANDREASEN, C.B. & BROWN, C.M., 1999. Lawsonia intracellularis-like organism infection in a miniature foal. Journal of the American Veterinary Medical Association, 215, 511–514.
3. HANNINEN, M.L....