Introduction Gram-positive irregular rods: Corynebacterium & Actinomyces

Genera that contain pathogens include Actinobaculum, Actinomyces, Corynebacterium and Trueperella. These are gram-positive pleomorphic rods or filaments and all the pathogenic members are non-motile. They are facultative anaerobes (Corynebacterium, Trueperella and some Actinomyces) or obligate anaerobes (some Actinomyces and Actinobaculum). All have an outer cell membrane rich in mycolic acids i.e. similar to Mycobacterium – this makes them more resistant to intra-vesicle destruction within host cells. Like Mycobacterium, they also tend to be intracellular pathogens occupying an intracytoplasmic niche in phagocytic cells. Corynebacterium and members of the Actinomycetales do not produce spores.

Their taxonomic position is shown below:

Common animal pathogens within the Phylum: Acinomycetota. (Those in purple boxes will be discussed in this chapter).

Infectious bacterial causes of abscessation in livestock

The table below provides a summary of the more important causes of abscessation in livestock that will require control strategies.

Other Actinomyces species

Actinomyces bovis, A. viscosus, Actinomyces suis. A. canis, A. israelii and A. hordeovuneris are known to cause pyogranulomatous infections in soft tissues secondary to trauma in a variety of animals. In dogs and cats they are a rare cause of pyothorax and intrathoracic granulomas that resemble tumours. Treatment includes surgical debridement and drainage and long-term treatment with penicillin or clindamycin.

Common causes of abscessation in livestock include the gram-positive cocci: Staphylococcus and Streptococcus; the gram-positive  pleomorphic rods, Corynebacterium pseudotuberculosis, Trueperella pyogenes and Actinomyces bovis; The gram-negative bacteria Actinobacillus lignieresii and Escherichia coli. The causes that are targeted are those that are either contagious or due to management circumstances, affect a large number of animals.

Epidemiology and pathogenesis of abscessation in livestock

Specific diseases

Caseous lymphadenitis of Sheep and Goats, Ulcerative lymphangitis in cattle and horses (Corynebacterium pseudotuberculosis). Also called “Cheesy Gland”

This widespread and important chronic and recurrent disease of sheep and goats results in lowered carcass weight, increased carcass trimming, and downgrading and devaluation of hides. In wool sheep it decreases clean fleece yield. Internal abscesses, such as those in the lungs, can cause chronic weight loss (thin ewe syndrome) and death. Note that this agent is one of the more important causes of weight loss in well nourished sheep. (Another infectious agent also present in Australia that causes chronic weight loss is ovine Johne’s disease caused by Mycobacterium avium ssp. paratuberculosis).  Cheesy gland is present in most flocks in Australia. Abattoir inspection reports indicate that cheesy gland is more common in Western Australia,  NSW and South Australia reporting herd prevalences of 97% , 91% and 88% respectively.  The incidence of abscesses steadily increases with age; clinical disease is more prevalent in adults, and up to 30% of animals in a flock can have superficial abscesses.

Sources of high numbers of C. pseudotuberculosis include ruptured abscesses or those cut open at shearing and coughing of sheep with lung infections. C. pseudotuberculosis enters via wounds causing an expanding non-painful abscess at this site or in the regional lymph node (superficial or external form), from which it may spread via the blood or lymphatic system and cause abscessation of internal lymph nodes or organs (visceral or internal form). Initial infection may cause no clinical signs or may be accompanied by high fever, anorexia, anaemia, and cellulitis at the infection site. If feed-associated, abscesses most commonly occur on the face and neck; if shearing-associated, abscesses are more common on the trunk and in the prescapular and prefemoral regions. Slow developing abscesses such as occur in sheep contain concentric rings of inspissated pus and fibrous tissue given an “onion skin-like” appearance. In goats the lesions develop more rapidly and the pus is creamy and thick. Pus is usually cream to slightly green or red-tinged and does not have a bad smell.

The disease in horses

Three manifestations have been described:

1.  Ulcerative lymphangitis where the lymphatic ducts in the subcutis are infected resulting in nodular swellings that resemble a string pearl necklace (resembles fungal infections of the subcutaneous lymphatics).

2. Equine pigeon breast (pigeon fever, dryland strangles, dryland distemper, false strangles, false distemper) where a large oedematous swelling develops in the lower pectoral region, ventral abdominal wall or groin. C. pseudotuberculosis biotype equi causing this infection is endemic to North America (high caseload in California) and is very rarely reported elsewhere in the world. Harness-related skin damage or the bites of tabanid flies and ticks are thought to play a role in this disease. Since the lesions cause pain, horses can be lame.

3.  Internal abscessation can also occur.

Useful reference: Gascoigne E, Ogden N, Lovatt F, and Davies, P (2020) ‘Update on caseous lymphadentitis in sheep’, InPractice, 42(2):105-114, doi:10.1136/inp.m455

Pyogenic infections caused by Trueperella pyogenes

This gram-positive pleomorphic rod that takes on a Chinese letter appearance in tissue is the most common cause of abscesses in cattle and pigs. (It has undergone several name changes including Corynebacterium pyogenes, Actinomyces pyogenes and Arcanobacterium pyogenes). This bacterium is found on the mucosa of these animals and will enter injured mucosa or skin causing a localised infection that can if not checked spread via the bloodstream and localise in several organs, including the joints, lungs, liver and nervous system. Common localised infections include the udder, feet, uterus in female and seminal vesicles in males. It often causes polymicrobial infections together with obligate anaerobic gram-negative bacteria such as Fusobacterium necrophorum or Dichelobacter nodosus i.e. summer mastitis in cattle, foot disease in sheep (see in obligate gram-negative anaerobe chapter) and cattle and liver necrosis in feedlot cattle and sheep. This bacterium when it causes a post-partum endometritis in cows can reduce the cow’s fertility and milk production.

The pictures below show sitting disease which happens in lambs when the tail is docked too short (ascending infection) and in cattle when there is micro-damage to the lumbar vertebrae , for example, by excessive riding by other cattle allowing blood-borne bacteria to settle in the damaged area and proliferate. 

An unusual condition is pituitary abscess syndrome. Where the purulent exudate and necrosis will develop in the pituitary fossa and adjacent structures of sheep, goats, cattle and horses. This can occur secondary to ear infections,  when animals head butt causing small wounds and when nose rings or nose plates are inserted. Clinical signs will occur suddenly and are variable. They include head pressing, bulging eyes, abnormal stance and recumbency.  Lesions are often unilateral and result in cranial nerve malfunction. The presence of bacteria and neutrophils within the cerebral spinal fluid is a useful diagnostic tool ante-mortally. Various bacteria have been implicated in this condition including T. pyogenes and E. coli.

Useful reading: Ribeiro MG, Risseti RM, Boanos CAD, Caffaro KA, de Morais ACB, Lara GHB et al (2015) ‘Trueperella pyogenes multispecies infections in domestic animals: a retrospective study of 144 cases (2002 to 2012)” , The Veterinary Quarterly 35:82-87, doi:10.1080/01652176.2015.1022667

Actinomyces bovis (Lumpy jaw)

Actinomyces bovis is an obligate anaerobe that is a commensal of the oral cavity of cattle where it causes a slowly progressive granulomatous disease of the jaws of 2-5 year-old cattle known as ‘lumpy jaw’. When there is trauma to the gums, i.e. periodontitis during change of teeth, rough feed or entrapment of grass awns in the periodontium, the bacteria can invade as shown in the pictures below.

They initially cause soft tissue inflammation and then penetrate into the bony tissue. Infection of the bone results in a chronic inflammatory response characterised by the presence of yellow granules known as Splendore-Hoepli bodies “sulphur granules” and pus. Destruction and remodelling of the bone results in an enlargement of the affected bone and facial distortion. Sinus tracts draining pus are also noted. The pus usually contains the ‘sulphur granules’ that consist of branching gram-positive bacterial filaments that are embedded in an eosinophilic matrix.   The bone takes on a honeycomb appearance and is easily fractured.

Actinobacillus lignieresii infections (Actinobacillosis, wooden tongue)

Actinobacillosis caused by Actinobacillus lignieresii, is a sporadic, usually chronic disease of cattle, sheep and goats and is characterised by pyogranulomatous inflammation particularly of the skin and other soft tissues of the head and mouth, and the regional lymph nodes. The bacterium occasionally causes abscesses or granulomas in the teats and udders of sows. Disease caused by A. lignieresii occurs throughout the world. Note that this is a gram-negative bacillus that belongs to the Family, Pasteurellaceae. It is dealt with here as it is a common cause of abscessation in livestock.

A. lignieresii occurs as a commensal on the oral mucous membranes particularly of ruminants. In cattle, sheep and goats, lesions may follow injury to the mucous membranes. In cattle lesions in the tongue tend to occur sporadically whereas lesions in the soft tissue of the face occur in outbreak form. Cattle use their tongue to prehend food and thus lesions are more frequent in the tissues of the tongue, the site of entry of the organisms often being the lingual groove. Occasionally lesions are seen in the soft tissue of the head where the bacteria enter via the gingiva. Abscesses occur infrequently in other sites such as the forestomachs, lungs and skin. Extension of the lesions occurs per continuitatum and by lymphogenous metastasis to regional lymph nodes that are frequently affected, the nodes being enlarged and firm. When the tongue is involved part of the organ becomes indurated, enlarged and immobile which interferes with eating and results in salivation and loss of weight. In mild cases the surface of the tongue becomes unevenly elevated. In severe cases the enlarged organ may protrude from the mouth. The thickened indurated lesions interfere progressively with prehension and mastication of feed and animals gradually starve to death.

The lesions are initially hard (resembling a fibroma), circumscribed nodules, varying in size from a few to several millimetres in diameter, some of which eventually become soft and fluctuate, and discharge their contents through the skin or mucous membrane, leaving deep ulcers or fistulae. These lesions may expand and extend into surrounding tissues.

Pus discharged from these lesions is thick, mucoid, greenish‑yellow to a bright yellow and odourless, and contains numerous granules, known as Splendore-Hoepli bodies ‘sulphur granules’ which have the appearance of grains of sand. Histologically, the Splendore-Hoepli bodies consist of masses of cocco‑bacilli which are embedded in a homogenous eosinophilic material having a palisaded outer circumference consisting of radiating finger‑like or club‑shaped structures. Around the granules is a zone containing mainly neutrophils but also macrophages and a few giant cells. Lymphocytes and plasma cells occur peripherally in the encompassing fibrous connective tissue which may be very dense in parts and replaces normal tissue structures in the vicinity.

Other bacteria such as Trueperella pyogenes, Streptococcus spp. and Pseudomonas aeruginosa are commonly found with A. lignieresii in lesions, and it is likely that they gain entry to tissues in the same way.

Diagnosis of abscessation in livestock

Diagnosis of the causes of abscesses, especially when there has been an outbreak of abscesses include the following:

1. Clinical examination or post-mortem examination to check for abscess distribution.

2. Gross evaluation of the abscess. Pus colour, consistency and smell. Also, look for the presence of granules.

3. Cytological evaluation of pus – type of inflammatory cell present, eosinophilic clubbing (Splendore-Hoeplii phenomena), gram positive or negative and bacterial morphology. (Refer to the table below)

4. Bacterial culture. Often required as a large variety of bacteria may cause abscessation. You are only taught the most common and those that may result in outbreaks or loss of valuable stock. (Refer to the table below)

5. Serology can be used as a herd test to screen flocks for the presence of C. pseudotuberculosis exotoxin antibodies. Because of its low sensitivity (87%) it should not be used to detect individual cases. It is also not able to distinguish vaccinated and recovered animals from those with active lesions.

Sample collection for bacterial culture

Bacteria are often difficult to culture from abscesses, mainly because they can be inhibited by the leukocytes and their products. Abscesses that have ruptured are generally contaminated with environmental or skin bacteria. Therefore select fresh – smaller, non-ruptured abscesses to collect a fine needle aspirate from or drain the abscess and inject the pus into a sterile screw cap plastic container. Collect a swab from the edge of the abscess. Always place the swab in a transport medium (i.e. Amies charcoal medium) that will protect obligate anaerobes.

When deciding whether to treat or cull clinically affected animals, the value and welfare of the animals should be taken into consideration. Internal abscesses in particular can be expensive to treat and can in some animals have a poor prognosis in spite of treatment. Thus livestock that are going thin are often humanely slaughtered. Note that animals with abscesses should be separated from unaffected animals due to the risk of organism transmission.

The treatment of external abscesses is surgical: (ripen), lance, drain into a container to reduce environmental contamination and flush the abscess cavity. In valuable animals deeper lesions can either be removed in toto or surgically curettaged. These lesions should be packed with tampons seeped in tincture of iodine.

Generally antibiotic therapy should be done as an adjunct to surgery. Antibiotic therapy for abscesses is often unsuccessful mainly because most antibiotics cannot reach bacteriocidal concentrations within the abscess. A number of antibiotics such as potentiated sulphonamides have reduced efficacy in pus. It is not always economically feasible to treat internal abscesses. Early in the disease amoxycillin can be used, later on more lipophilic antibiotics such as the macrolides can be used.

Prevention

In the case of abscessation, prevention is far more effective and should include the following:

1. Management changes – investigate any predisposing factors and correct them e.g. reduce too coarse feed, don’t feed too soft feed if it gets stuck between the teeth, don’t dock tails too short, debud horns early, disinfection of the umbilicus in neonates in small camps, remove sharp objects that can injure animals, good stock management to avoid fighting and riding, Good wound and hygiene management when shearing fibre producing animals – shear young animals first, shearers should use cleaned and disinfected blades and clean overalls provided by the farmer, they should treat any wounds straight away – the list goes on.
2. Rear young stock separately from old stock. Old stock are more likely to have abscesses, especially due to C. pseudotuberculosis.
3. Good wound care. Early identification of animals with abscesses, isolate and treat them. To avoid environmental contamination, pus should be drained from the abscess into a container and safely disposed of.
4. Vaccines are available for the protection of sheep and goats against CLA (C. pseudotuberculosis). They are usually as part of multiantigen vaccines. The killed bacterin (i.e. Webster’s 6 in 1 B12) or toxoid (i.e. GlanEry 7 in 1; Cooper’s Guardian 6 in 1) vaccine is protective and should be administered at marking (3 months of age), a booster given at weaning (1 month later) with 6 monthly (high exposure) or annually (low exposure). The annual vaccine should be timed to be administered about 1 month prior to expected injury i.e. shearing. Research has shown that full vaccination can reduce the disease prevalence to 3%. Don’t use in animals that may already have been exposed to C. pseudotuberculosis as they may show adverse reactions such as lethargy and lameness. Additionally in an eradication programme, when the disease prevalence is low, vaccination can be stopped and any seropositive animals slaughtered. Any new additions to the flock should be young, free from lesions and seronegative. (Some countries have a bacterin vaccine effective against T. pyogenes and some will produce an autogenous vaccine against T. pyogenes).

Contagious cystitis and pyelonephritis in cattle

Learning Objective

Identify and manage cattle suffering from contagious pyelonephritis.

Bacterial infections of the urinary tract are most common in multiparous, post-parturient cows (about 83 days post-partum). Although the disease distributed globally, its occurrence is sporadic and prevalence low. The most common causes are members of the Corynebacterium renale group viz. C. renale; C. cystitidis; and C. pilosum. These bacteria are commensals of the vagina and prepuce and can be spread from cow to cow via urine droplets or iatrogenically via AI catheters. These infections are contagious infecting up to 1.5% of a herd. 

Escherichia coli can also cause cystitis and pyelonephritis in cows but tends only to infect individual cows. Anatomical defects (i.e. trauma due to partus) as well as a high protein diet (increased urine pH) is conducive to the colonisation and proliferation of bacteria. These bacteria once infecting the bladder gradually move up the urinary tract using adhesion fimbrae eventually reaching the pelvis of the kidneys. Bacteria affecting the urinary tract usually produce the enzyme urease which allows them to utilise urea as an energy source. Most of the cellular damage is associated with the inflammatory response.

Initially cattle have a haematuria, later they develop a fever, are anorexic, urinate frequently and often with difficulty, show colic. The urine contains pus and when the cow will become uraemic and go into renal failure exhibiting polydipsia and polyuria. On rectal palpation the bladder appears thickened, there will be thickening of the ureter/s and the lobation of the kidneys will be reduced (usually the left kidney is more affected).

The diagnosis is based on the clinical picture and confirmed by blood biochemistry (high urea and creatinine levels), urine examination and culture.

Penicillin or potentiated sulphonamides can be used in the case of Corynebacterium infections. The urine should also be acidified and fluids dosed to maintain urine perfusion. Note that once the cows are severely uraemic with high blood creatinine levels, the prognosis is poor and cows should be humanely euthanised. Affected cows should be housed separately and milked last to prevent urine splash transmission.

Porcine cystitis-pyelonephritis complex

Learning Objective

Compare the epidemiology of the porcine cystitis-pyelonephritis complex with opportunistic infections of the urinary tract in pigs.

Sows and gilts due to the intensive nature of farming are especially susceptible to opportunistic ascending infections of the urinary tract. Rarely venereal infections occur in non-immune gilts that are naturally mated.

The table below compares urinary tract infections caused by opportunistic pathogens to the venereal pathogen Actinobaculum suis.

The diagnosis is based on the observation of frequent urination with blood stained urine and urine analysis. The diagnosis can be confirmed by culture. Note that the bacterium is an obligate anaerobe so at post-mortem large kidney samples or sending the whole bladder with the neck of the bladder sealed with twine may improve its isolation.

Treatment: Usually ampicillin/amoxycillin and acidification of the urine using feed grade citric acid. Washing of sows and maintaining good hygiene in the farrowing crates will decrease the environmental load. Frequent urination should be encouraged by providing free access to clean water and allowing sows to stand and ensuring that they are not overweight. Regular culling of sows to ensure the proper parity is maintained in a herd.

END OF CHAPTER