Introduction to the Spirochaetes

Spirochaetes are fine, helically-coiled, bacteria. They have flagella (axial filaments) that attach in the cell membrane and run between in inner (peptidoglycan layer) and outer membrane (LPS layer in Leptospira and Brachyspira, but not Borrelia) which allows them to move in a cork-screw fashion and enables them to move through viscous fluids such as mucus. These bacteria are only found in moist environments as they are very susceptible to desiccation and pH extremes. Dark-field or fluorescent microscopy is used to visualise these very thin, strand-like bacteria.

diseases caused by the spirochaetes

Whilst the spirochaetes are common in watery environments only a few cause disease. In animals the most important disease caused by this group is leptospirosis.

Below is a Table listing the  of diseases in animals caused by the spirochaetes.

Refer to the chapter on vector-borne bacterial diseases for those diseases in the list transmitted by ticks. Contagious ovine digital dermatitis is discussed in the chapter on infectious foot disease and necrobacillosis.

Leptospirosis

Leptospirosis is a global, contagious, multisystemic disease of animals, including humans caused by pathogenic members of the aerobic spirochaete Leptospira. It infects all mammals but  very few exhibit clinical signs of disease. It is a ZOONOSIS and notifiable in people, NOT animals It is an important disease of the Tropics in cattle, pigs and dogs. Outbreaks of leptospirosis are often associated with heavy rainfall and flooding.

To find out more on Leptospirosis:

1. Ellis W.A. (2015) Animal Leptospirosis. In: Adler B. (eds) Leptospira and Leptospirosis. Current Topics in Microbiology and Immunology, vol 387. Springer, Berlin, Heidelberg
2. Sykes, JE, Hartmann K, Lunn KF, Moore GE, Stoddard RA, Goldstein RE (2010) 2010 ACVIM Small Animal Consensus Statement on Leptospirosis: Diagnosis, Epidemiology, Treatment, and Prevention. Journal of Internal Veterinary Medicine:, 25: 1-13. https://doi.org/10.1111/j.1939-1676.2010.0654.x

Morphology of Leptospira

Leptospires are obligate aerobes with an optimum growth temperature of 28 – 30°C. They cannot tolerate desiccation (drying out) nor will they survive temperatures <18°C or >40°C. This means that they can survive for up to 6 months in fresh waters that are warm and slightly alkaline.  They survive for a much shorter period in drier soils. Evidence suggests that pathogenic leptospires are found in riverbank soils and soil sediment where they form biofilms. Thus heavy rainfall and flooding can flush leptospires in soil and urine into freshwater. Cases in temperate climates are more sporadic and are often associated with a unique epidemiology i.e. venereal transmission or urine splashing in crowded barns or pens. An increase in rodent numbers (maintenance hosts) can also lead to increase in the number of cases.

Leptospires have a typical spirochaete shape with hooked ends this allows them to attach to mucosal surfaces and use their corkscrew-like motility to bore themselves through the mucosa.  This means that the leptospires can enter the host by any route. However, the most common routes of entry are the mucosae of the mouth, nasal cavity, eye and external genitalia. Direct transmission is by urine splashes, venereal, contact with aborted foetuses and placental material, animal bites and infected milk. Leptospires eliminated in the urine of carrier animals contaminates freshwater bodies where it crosses all mucosae as well as abraded or water softened skin.

Carrier animals

Leptospires are maintained in the proximal tubules of the kidneys of apparently healthy mammals, so-called “maintenance hosts” (see Table below) and shed intermittently into the urine. These are usually immune animals where the immune system tolerates the bacterium in certain body sites such as the proximal tubules of the kidneys and eyes. Non-immune maintenance hosts tend to show mild or chronic disease.

It is only when non-host adapted serovars of Leptospira infect “accidental hosts” that serious disease occurs. These people and animals are only temporary carriers of these leptospires.

The agglutinating surface antigens of pathogenic leptospires classify into 24 serogroups and over 250 serovars. Serogroups are not cross-reactive, but serovars within a serogroup can be. Pathogenic serovars distribute into 20 genomospecies where most infections are associated with Leptospira interrogans and Leptospira borgpetersenii. Interestingly, L. interrogans can survive in low nutrient conditions, whereas L. borgpetersenii does not.

Below is a Table showing some of the more common Leptospira serovars and their maintenance hosts in Australia.

Serovar distribution is geographical.  In Australia, disease is recognised in cattle (serovars Hardjo, Pomona and Zanoni), pigs (Pomona, Tarassovi and Bratislava), sheep (Hardjo), horses (Pomona), dogs (Copenhageni, Australis, Hardjo), and humans (mainly Arborea, Zanoni, Hardjo and Australis).   Although antibodies have been detected in snakes and some serovars in frogs their role in disease is unknown. Interestingly, leptospirosis has been recognised in pinnipeds off the Californian coast even though the marine environment is unlikely to support the bacterium.

Pathogenesis of leptospirosis

Leptospires invade the body through the intact mucous membranes of the eye, upper respiratory and oropharyngeal cavities and urogenital tract as well as broken or water softened skin. Whilst not fully understand, leptospires use outer membrane proteins to attach to cell surfaces before they invade. They are able to resist Complement-mediated lysis by cleaving Complement or stimulating the regulatory enzymes used to moderate the activation of Complement. Bacteraemia is present and lasts until antibodies develop, usually for up to 7 days. Initially the leptospires will localise in the liver and after a short secondary bacteraemia, they localise in other organs, especially the eye, kidney, placenta and udder. Long-term survival of leptospires is usually in tissues that have a lowered immune response i.e. immune privileged sites. The lesions in tissue result from endothelial damage to the capillary beds resulting in ischaemic necrosis.  Focal areas of necrosis may be replaced by fibrous tissue observed as white spots i.e. “white spotted kidney”.  Virulence factors have not been properly studied but sphingomyelinases – porins, surface LigA and LigB proteins, surface lipoprotein LipL32 place a role in cell adherence and invasion. Humoral immunity directed to leptospiral LPS is protective in most species. Cattle are unusual in that immunity is TH1 with gamma-interferon release.

Below is a diagrammatic representation of the pathogenesis of leptospirosis

Clinical signs of leptospirosis

Most infected animals show no or mild signs of disease. The incubation period is 2 to 20 days, although it is longer for the chronic form. Clinical signs are associated with the lesion site.

Peracute disease

The peracute form, occurs in the bacteraemic stage of the disease and is more common in foetuses, neonatal animals and highly susceptible dogs. It manifests as intravascular haemorrhage with petechiation and haemoglobinuria.

Acute disease

The acute form manifests as acute liver and/or renal failure. In dogs, the acute form is most recognised where dogs present with fever, icterus (yellow gums), vomiting, diarrhoea and uraemia. Haemorrhages, DIC and death occur in some dogs. This form also occurs in people.

Chronic disease

The chronic form of the disease is the most common in animals with abortions, stillbirths and weak neonates being the most common clinical evidence of disease in ruminants, pigs and horses. In cattle a drop in milk production due to an infected udder results in the so-called “flabby udder”. In horses, equine recurrent uveitis (ERU), periodic opthalmia, or “moon blindness” is recognised. Associated with Leptospira infections of the eye, ERU, an autoimmune inflammatory disease results in recurrent bouts of blindness where the eye appears cloudy. Eventually, it will lead to permanent blindness in the affected eye. All animals, but especially dogs, develop chronic interstitial nephritis (CIN).

Leptospirosis in people

Leptospirosis in humans is usually an occupational or recreational zoonosis affecting those working in the agricultural sectors (livestock, sugar and rice farming) and those involved with aquatic sports. Massive outbreaks occur post-flooding especially in tropical countries where socio-economic conditions are poor and rats are allowed to proliferate. In humans, most infections tend to be mild with symptoms of headache, fever, chills, sweats and myalgia (muscle pain).  Some highly pathogenic serovars may cause pulmonary haemorrhaging or renal and liver failure (Weil’s disease) which can result in death. 

Diagnosis of leptospirosis

Note that the case history, including epidemiological indicators, and clinical signs of leptospirosis in animals would ensure that leptospirosis is included in the differential diagnoses list.  A thorough disease investigation is necessary to confirm a diagnosis.

Detection of organism

• Blood and organ biopsies in acute disease and urine,
• Foetal fluids and membranes, and aqueous fluid of the eye in chronic disease

to be submitted for qPCR or culture. Culture can take up to 2 months and sample contamination makes the isolation of leptospires difficult.

Spirochaetes can be observed in the tissue of recently dead animals using a Silver staining method. However, the leptospires decompose rapidly in deceased animals. Thus qPCR that detects the lipL32 surface encoding gene in all pathogenic leptospires remains the most reliable diagnostic technique, especially when diagnosing peracute and acute leptospirosis.

Detection of antibodies

Antibody detection on serum or clotted blood using either an ELISA for Leptospira genus or microscopic agglutination test (MAT) for serogroups (cross-reactions occurs in serovars within a serogroup) is the most common means of diagnosis. In acute infections a 4-fold rise in antibody titre demonstrates that the infection is recent. This is not the case in chronic infections, where the antibody titre may be high at the time of clinical disease. A lateral flow assay is available to detect antibodies to Leptospira in dogs. This is the most common way leptospirosis is diagnosed in dogs.

control including treatment of leptospirosis

• Antibiotic therapy and supportive therapy is used to treat leptospirosis in companion animals
• Annual vaccination with a bacterin vaccine for high risk animals (see below)
• Good rodent control and make sure that there is no feed accessible that is attractive to rodents and other wildlife
• Avoid swimming in and drinking from stagnant, freshwater pools during the warm summer months
• Purchase livestock from farms with an animal health statement
• Good biosecurity plan on farms focusing on animal purchasing and movement policies
• The urine of sick and carrier animals and the birth fluids of infected animals are rich in leptospires. Wear gloves and clean up urine with disinfectants. Exposure of outdoor areas to sunlight and allowing water to drain away will kill the bacteria.

Available bacterin vaccines in Australia (no need to learn vaccine names, just for what species and when)

Pigs

• Lepto-Eryvac^® Zoetis pig vaccine against Leptospira Pomona and Tarassovi & Erysipelothrix rhusiopathiae. Vaccinated at 4 weeks of age, booster 4 weeks later and thereafter every 6 months.
• PLEvac^® MSD Against L. Pomona and porcine parvovirus
• ECOvacLE^®  MSD Against L. Pomona, E. coli and E. rhusiopathiae

Cattle

Post-mortem findings are usually quite clear, although the disease can be confused with Lawsonia intracellularis infection (proliferative enteritis); intestinal spirochaetosis, salmonellosis, Trichuris (whipworm) infestation and gastric ulcers.

The mucosa of the large intestine is oedematous and congested, thickened (folded) and is often covered with a fibrinous diptheritic membrane (fibrinohaemorrhagic typhlocolitis).

Histologically, epithelial hyperplasia is a feature. A crystal violet stained smear of the mucosa of the proximal large intestine will reveal numerous fine, spirochaetes. Silver staining of histological sections of recently dead animals will reveal numerous thread-like organisms in the intestinal crypts.

Samples of the affected intestine are collected for anaerobic bacterial culture and antimicrobial susceptibility testing. Identification of the bacteria can be done using a species specific qPCR.

The disease is usually treated using antibiotic medication of drinking water with bacitracin, lincomycin or the macrolides – tylosin, tiamulin, valnemulin or aivlosin are used.  Carbadox or monensin is used in countries where they are registered. However, antimicrobial resistance is common and therefore it may be necessary to test for antibiotic susceptibility.

Further control measures include rodent control, antibiotic treatment of carrier pigs and good farm sanitation and taking measures to avoid spread between pens (slatted floors, solid partitions, disinfectant pans, all-in-all-out). Avoid reusing untreated waste water.

Eradication of the agent has been done by early weaning at 3 weeks of age and transportation of the piglets to a clean site. Destocking by selling all the other pigs and then repopulate after disinfection of the pens using these pigs.  Complete depopulation can also be done with repopulation, by Brachyspira-free pigs in clean disinfected quarters.

To date vaccination has been unsuccessful.

Subcutaneous infections caused by the Spirochaetes

The skin diseases shown below are rare, so will not be tested.

Bovine digital dermatitis (BDD) (hairy warts) is a severe infectious cause of lameness with lesions at the horn junction at the back of the foot near the interdigital area which has spread through dairy cattle populations worldwide, causing serious welfare and agricultural problems. An erosive and proliferative form occurs. Treponema species together with other mixed bacterial infections originating from slurry have been implicated as the cause. Treatment involves cleaning the foot and using tetracycline footbaths, sprays or dressings. Improvement in environmental hygiene is also necessary. Note that “Ovine digital dermatitis” which is common in the UK (see notes on ovine footrot) is caused by  a variety of Treponema species.

Ulcerative  granuloma is a rare granulomatous skin disease in pigs is caused by an uncharacterised spirochaete together with secondary infections with other bacteria including streptococci and staphylococci. The bacteria enter via wound contamination and cause severe localised inflammation and the development of fibrous tissue. Control involves improving hygiene, reducing trauma and identifying the areas within the management system where infection first starts and making changes to these. Infected pigs can be treated with penicillin, tiamulin or lincomycin.

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