Introduction

The curved to spiral, gram-negative, oxidase positive bacteria can be divided into the fermentative bacteria such as Vibrio, Shewenella and Aeromonas and the non-fermentative bacteria: Campylobacter, Arcobacter, Helicobacter and Lawsonia. Vibrio, Shewenella and Aeromonas species are found in watery environments and thus are known to cause a number of diseases of aquatic animals.

Within the Phylum Campylobacterota is Campylobacter.  Thermophilic Campylobacter species are the cause of gastroenteritis in people (zoonosis) and animals and abortion in sheep whereas the mesophilic Campylobacter species cause reproductive disease in ruminants. Other bacteria in this group that are occasionally encountered as pathogens are Helicobacter a cause of gastroenteritis and gastric ulceration and Arcobacter a cause of diarrhoea. (You do not have to learn about Helicobacter or Arcobacter).

Similar in morphology, but found within the Phylum Thermodesulfobacteriota, is the obligate intracellular bacterium, Lawsonia intracellularis, a cause of proliferative ileitis in pigs, foals and rabbits. It will be taught in the Chapter.

Diseases caused by the small curved gram-negative bacteria

A list of the diseases and their natural habitat is shown in the Table below.

Background information on less important bacteria in this group (no need to Learn)

Helicobacter infections

Up to 35 Helicobacter species have been identified some are inhabitants of the submucous layer of the pyloric crypts of the stomach of mammals and humans and others of the lower intestinal tract and liver. The bacteria survive in stomach by producing the enzyme urease which reduces the acidity of the environment. In people the gastric helicobacters are the cause of gastritis, peptic ulcers and predisposes to stomach adenocarcinomas. Helicobacter suis is associated with gastric ulcers in pigs and the canine and feline helicobacters with gastritis in those species.

Arcobacter infections

This bacterium is related to Campylobacter, but unlike Campylobacter it is aerobic and can be found both in the intestine as well as watery environments. Some species are also found in marine environments. They are rarely implicated in disease where they can cause watery, persistent diarrhoea and abortion. Like Helicobacter, pathogenic species are able to disrupt the integrity of the tight junctions between cells and cause cell necrosis.

Campylobacter

Campylobacter (meaning “twisted” bacterium) are curved gram-negative rods that are microaerophilic (grow in reduced oxygen), have complex growth requirements and are either found in the intestinal tract (thermophilic species) of warm-blooded animals or on the mucosa as mesophilic species. They are oxidase-positive and have polar or bipolar flagella and therefore move in a typical corkscrew pattern. They are usually very susceptible to harsh environments and chemicals. These bacteria cause a variety of diseases (see Table above) in animals and humans.

Thermophilic Campylobacter species

The thermophilic species (grows at 42°C) Campylobacter jejuni and Campylobacter coli are common inhabitants of the intestinal tract of warm-blooded animals, but only rarely cause intestinal disease in their animal hosts.

They do, however, cause a zoonotic disease in susceptible humans. It is the most common recorded zoonosis in developed (G1) countries, including Australia (41 428 cases reported in 2023).

People become infected by the ingestion of undercooked meat especially poultry (50% of cases), unpasteurised milk, unchlorinated water and with contact with infected animals. The meat is often contaminated at the meat works where in the processing of the carcass it is transferred from the intestines to the meat. Offal and the liver will have a high number of Campylobacter. Another means of transmission is via pets. Dogs, especially puppies are intestinal carriers of Campylobacter and pass it on to people handling them by the faecal-oral route.

Infection is via the ingestion of this faecal bacterium which then is attracted to mucin 2 on the intestinal epithelium. In people, the infective dose is low – 500 bacteria or less. CiaB proteins produced by the bacterium encourage the epithelial cells to ingest it. The bacteria exit the phagocyte and divide,  causing cell necrosis. The bacteria then penetrate deeper inducing an inflammatory response by the host.  Most strains of C. jejuni produce a cytolethal distending toxin (CDT) that hinders the cells from dividing and causes cell apoptosis. It also produces phospholipase.

Clinical signs of diarrhoea and vomiting are usually noted with 2 to 5 days after infection. Most infected people develop a self-limiting diarrhoea, fever, malaise and abdominal pain of 2 to 4 days of duration. In some people the diarrhoea will be bloody and they may vomit. In up to 20% of people the diarrhoea will last for more than 1 week. Guillain-Barré syndrome, an autoimmune paralytic disease, may develop 2 – 3 weeks later in 1 out of 2000 cases. This syndrome has been linked to O:19 and O:41 serotypes of C. jejuni. This is an example of antigenic mimicry, where the antibodies produced against the liooligosaccharide of these C. jejuni strains will also attack the antigenically related human GM1 ganglioside. Reiter’s syndrome (a reactive arthritis) can also occur in genetically-predisposed individuals.

Diagnosis of the disease is by a faecal swab or faeces that are placed in Carey-Blair transport medium and the bacteria cultured on selective media in an atmosphere of 10% CO₂, 6% O₂ and 85%N_2. It is then identified by phenotypic tests or by qPCR. (In people, the disease is a group B agent and a written notification occurs within 5 days of the diagnosis or when the laboratory isolates the bacterium from drinking water or food).

Treatment is rarely required in animals. Fluoroquinolone antibiotics are usually used to treat human patients with severe disease. The presence of fluoroquinolone-resistant C. jejuni and C. jejuni in meat originating from especially poultry, but also cattle and sheep is of concern. In fact this is the primary reason why the use of fluoroquinolones has been banned in food animals.

Humans can protect themselves from becoming infected by only eating fully cooked meats (especially poultry – cooked to the bone); preventing cross-contamination in food preparation making sure that raw meat and vegetables and fruit are not handled at the same time without hand washing and the use of separate implements; washing hands after being with animals; and by not drinking unpasteurised dairy products.

If necessary, measures can be taken to exclude the agent on broiler farms, by maintaining closed houses, excluding rodents, birds and insects, having strict biosecurity, an all-in-all-out management system and chlorinating the water. The use of probiotics and vaccination are under investigation. Withholding food for 12 hours prior to slaughter and disinfection of transport boxes will decrease faecal contamination of carcasses.

Spotty liver syndrome in layer birds

Campylobacter hepaticus a newly identified thermophilic Campylobacter is the cause of spotty liver in young birds at peak lay, especially large, free-ranging layer flocks. This disease has been recognised in Australia for more than 60 years, but has only recently become economically important as its prevalence is high in free-ranging layers, causing a rapid, but persistent drop in egg production (35%) and up to 15% mortalities. Modern organic farming and welfare issues have led to a huge increase in free-range poultry production systems. The disease occurs in the hottest months of the year. Death occurs quickly with all the birds showing liver pathology with the presence of small, multiple areas necrosis on the liver. A diarrhoea is often present.

Diagnosis is mainly by qPCR of liver and bile samples. Cultures can also be attempted using the same methods as for C. jejuni and C. coli.

In Australia chlortetracycline and lincomycin are commonly used to treat spotty liver syndrome. Both have a nil day withdrawal period in eggs. However, antimicrobial resistance to these two antibiotics is developing, requiring the use of alternative antibiotics. Other control measures include excellent biosecurity and infection control methods as well as installing cooling fans. There is currently no commercial vaccine available.

Bovine genital campylobacteriosis

Bovine genital campylobacteriosis is a venereal disease of cattle caused by C. fetus subsp. venerealis or occasionally C. fetus subsp. fetus that resulting in early embryonic death, infertility, a protracted calving season, and occasionally abortion. Campylobacter fetus subsp. fetus has been implicated in abortions of cows and ewes.

The bacterium lives in the mucus of the preputial and penile epithelial crypts where it does not stimulate an immune response or any lesions in the bull. Younger bulls tend to be transient carriers whereas bulls over 3 years of age with deeper and more enfolded crypts that sustain a microaerophilic environment tend to be permanent carriers.

Coitus allows the bacterium to be deposited in the vagina of a cow. Once in the vagina and uterus the bacterium elicits an inflammatory response leading to a mucopurulent cervicitis and endometritis. The uterine environment becomes unsuitable for implantation or the survival of early embryos. This is clinically observed as prolonged oestrous cycles, repeat breeding and in farming management systems that have a narrow breeding season (restricted joining) as a prolongation of the calving season or high numbers of empty cows. Most cows will within a few cycles throw off the infection and breed. They start to produce IgA and IgG which opsonises the bacteria allowing them to be destroyed by the immune system. However in up to 30% cows (especially heifers) the infection will spread to the oviducts causing a salpingitis and they will become permanently infected and the cows can become infertile. Cows that have been infected develop a strong and long-lasting immunity. Therefore in endemic herds, infertility is more common in heifers

Diagnosis

Even though bulls are unaffected carriers, they are a target for disease control. Thus, the detection of C. fetus subsp. venerealis is more often carried out on the bull. Sampling is done by scraping and aspirating the preputial and penile mucosa of bulls with a sterile pipette. The contents are flushed into phosphate buffered saline, allowed to settle and the suspension placed in Campylobacter transport medium i.e. Clark’s medium and sent to the laboratory for culture, real-time PCR or fluorescent antibody testing. Since the bacterium is very labile, the sample should be cooled and reach the laboratory preferably in the same day. To improve the test accuracy repeat testing should be done a week later.

An ELISA will detect C. fetus specific sIgA antibodies in the vaginal mucus.

Other infectious causes of embryonal loss or an infertility syndrome include Tritrichomonas foetus and bovine genital ureaplasmosis caused by Ureaplasma diversum.

Control

Vaccination is the most practical means of control. The bacterin vaccine is administered twice to bulls and once to heifers and cows 7 months to 30 days prior to joining. Bulls are then vaccinated annually 3 weeks prior to joining. Vaccination in bulls leads to immunity, which means that most will self-cure. However, treatment of the prepuce with amoxicillin at the same time as the 2nd (booster) vaccine will assist in eliminating the bacterium.

Where practical, herds should breed from bulls tested free of Campylobacter fetus subsp. venerealis or use artificial insemination from antibiotic treated semen. Older bulls are at higher risk of being permanent carriers, so use only young bulls for breeding in infected herds. The prepuce of valuable bulls can be treated with topical antibiotics to remove the infection. However, they should be tested Campylobacter free before being used for breeding.

Ovine campylobacteriosis

Campylobacter fetus subsp. fetus and C. jejuni have been implicated in abortion in the last 8 weeks of gestation or stillbirths in sheep and occasionally goats and cattle. Abortion usually occurs 7 – 25 days after ingestion of an infective dose and between 10 to 50% of ewes will abort where the agent has been newly introduced.  The disease is more common where sheep are intensively farmed.

Death of the foetus is primarily ascribed to a placentitis where the foetal cotyledons are infected and sometimes the intercoyledon area is covered in brown exudates. This is in contrast to abortions caused by the protozoan Toxoplasma gondii where white necrotic foci are noted on the foetal cotyledons. The foetal liver is affected in 10-30% of cases showing focal areas of necrosis. The disease is provisionally diagnosed by looking at the characteristic motility of the bacterium in wet preparations of the abomasal contents or by Gram staining of the affected material as well as abomasal contents. Cultures or qPCRs are done on the aforementioned samples to confirm the diagnosis.

Once an abortion storm has started little can be done to protect the flock. However, environmental contamination should be reduced by collecting and destroying any aborted material, foetuses and uterine discharges. The disease prevalence can be reduced by annual vaccination using the Ovilis Campyvax (Coopers) that contains bacterins of Campylobacter fetus subsp. fetus and Campylobacter jejuni subsp. jejuni.  Care must be taken when handling aborted material as both bacteria can infect people (ZOONOSIS) via ingestion.

Lawsonia infections: Proliferative enteropathies in piglets and foals

Proliferative enteropathies in foals and piglets are caused by an anaerobic, obligate intracellular, gram-negative, curved, motile bacterium known as Lawsonia intracellularis. Although this bacterium is similar in morphology to Campylobacter/Arcobacter it is unrelated genetically. It belongs to the Family Desulfovibrionaceae. Equine strains have been found to be more related to rabbit strains than pig strains.

The bacteria, once ingested, are assisted by helper bacteria in the intestines to adhere to and invade the immature intestinal epithelial cells of the small intestine, predominantly the ileum at the Peyer’s patches.

Infected cells proliferate, increasing the intestinal wall thickness as well as preventing cell maturation. This results in malabsorption of nutrients with the consequence of chronic diarrhoea, hypoproteinaemia and weight loss. Inflammation of these cells results in a low grade fever. Grower pigs and foals between 2 to 12 months of age are most susceptible to the disease and are usually smaller than their litter mates, are thin and have a potbellied appearance.

In pigs various manifestation of the disease are recognised, namely:

• The uncomplicated form known as porcine intestinal adenomatosis (PIA)
• Porcine haemorrhagic enteropathy (PHE) – a bleeding syndrome seen in older pigs, predominantly gilts whose clinical signs can be confused with gastric ulcers. The pigs are pale and produce black tarry stools (malaena). It is believed to be caused by an autoimmune response to the bacterium.
• Necrotic enteritis (NE) – where the affected intestine is markedly inflamed covered by a diphtheritic membrane. Usually the damage is exacerbated by secondary bacterial infection.
• Regional ileitis (RI), a chronic manifestation of the disease, where the affected ileum becomes so thickened that ingesta cannot pass through. The picture of RI on the left shows the narrowed intestinal lumen. A complication of this is intestinal rupture and peritonitis.

The Table below provides pictures of the intestines taken during post-mortem examination

Diagnosis

The disease is diagnosed by a combination of serology and qPCR of faeces. Intestinal biopsy samples taken either surgically or at post-mortem are also diagnostic. Silver staining of histological sections will reveal numerous small curved bacteria in the apical area of the intestinal cells. In foals abdominal ultrasound has been used to detect thickened intestines. This disease must be distinguished from swine dysentery caused by a spirochaete known as Brachyspira hyodysenteriae.

Serology can be used as a herd test to detect positive farms.

The table below shows the most important means of distinguishing the two diseases. The diagnosis PCR is a multiplex one that will detect the presence of Lawsonia– and Brachyspira-specific DNA.

Control

The disease is controlled in foals by recognition of the index case and using this information to isolate and monitor sick and at risk animals. Treatment of foals includes supportive therapy with correction of hypoproteinaemia (hydroxylethyl starch and plasma) and antibiotics mainly the macrolides in combinations with other antibiotics such as rifampicin and doxycycline. The antibiotics are administered for 2 to 3 weeks. Trials using the swine vaccine either via either oral or rectal administration afford some protection in foals.

On endemic pig farms an oral, live attenuated vaccine (Enterisol Ileitis, Boeheringer) administered to piglets from 3 weeks of age decreases the prevalence of disease. Do not administer antibiotics 3 days before and 3 days after vaccination. If it is not possible to avoid the use of antibiotics, an intradermal, inactivated bacterin vaccine can be used (Porcilis Lawsonia IDL inactivated vaccine, MSD Animal Health, Australia).  Endemic farms are those with a clinical history of proliferative enteropathies or evidence of antibodies to L. interacellularis.

In pigs an all-in-all-out system reduces exposure of the susceptible piglets to older carrier pigs. These pigs may also be treated with antibiotics such as tylosin or oxytetracyline in the water for 5 days. Furthermore good on-farm hygiene, with regular pen cleaning and disinfection with quaternary ammonium compounds and exposure to sunlight will reduce the bacterial burden. Strategically medicate incoming gilts with tylosin or other antibiotics if there are problems, commencing one week before signs usually appear. Continue for four weeks as under treatment.

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