Introduction

Clostridia are gram-positive large regular rods that are generally motile and produce resistant endospores. They are also obligate anaerobes. Pathogenic species are generally commensals within the gastrointestinal tract of animals and produce some of the most potent exotoxins known. Thus many clostridial diseases have a peracute to acute manifestation and vaccines directed at the development of antitoxin antibodies are protective. Clostridial diseases are often confused with other toxicities and septicaemic diseases that cause sudden death in animals.

Aetiology

1. Relate the biology of the clostridia to their growth and survival in the gastrointestinal tract and environment

Clostridia are gram-positive, large regular, rods that are generally motile and produce resistant endospores. They are usually obligate anaerobes that ferment sugars and break down proteins with gas production. Thus, they are easily recognised morphologically. Another means of grouping the clostridia, is the position in the bacterium where their spores are found.

This means that their vegetative forms are only found in anaerobic environments i.e. as a commensal in the gastrointestinal tract of animals and humans; contaminated haylage and silage; bone marrow; water sediments contaminated canned foods. The dormant endospores which are expelled with faeces can reach high levels in the soils of densely populated animal pens or camps. These spores are highly resistant to disinfection and can easily contaminate meat processing plants, dairies and veterinary clinics/hospitals.

Group the pathogenic clostridia based on their disease-causing ability

The diseases caused by this genus can be broadly divided into 3 groups:

• Enterotoxic: Clostridium perfringens toxin types A to D and Clostridioides difficile
• Histiotoxic: Clostridium septicum, Clostridium chauvoei, Clostridium novyi and Clostridium sordelli. (Clostridium piliforme)
• Neurotoxic: Clostridium botulinum and Clostridium tetani

Enterotoxic: Clostridium perfringens infections

Clostridium perfringens is the most widely distributed potential pathogen in nature and occurs in soil, sewage and water, as well as in the intestinal tract of humans and warm-blooded animals. Clostridium perfringens often causes non-transmissible diarrhoea and septicaemia that is associated with stress, rapid dietary changes and high environmental loads of bacterial endospores. Clostridium perfringens is a gram‑positive, squat, non‑motile bacillus, which forms capsules in tissue and sub-terminal spores in the environment.

Explain the factors that contribute to Clostridium perfringens overgrowth in the intestines and consequently the pathogenesis of associated diseases.

Clostridium perfringens,  a normal inhabitant of the large intestine, proliferates in the intestines when there is an increased supply of proteins. This is because C. perfringens lacks the enzymes required to synthesise many essential amino acids. Thus periods of reduced eating followed by overeating can lead to the delivery of undigested food to the large intestine. Environmental stressors such as excessive heat can lead to irregular feeding patterns. Diseases caused by Clostridium perfringens are often referred to as ‘overeating diseases’.

Furthermore, any increase in mucus production or damage to the intestinal tract leading to increased protein leakage or decreased protein absorption provides additional food sources for these bacteria. This happens when there are concurrent infections such as coccidiosis, other intestinal parasites, mycotoxins and viral diseases. Necrotic enteritis in poultry is usually associated with intestinal coccidiosis. C. perfringens is able to colonise and break down intestinal mucins, allowing the bacteria to adhere directly to intestinal cells. Their rapid growth rate as well as the ability to reach intestinal cells allows bacterial exotoxins to be more effective.

Furthermore, periods of high rainfall with animals living in muddy and faecally-contaminated conditions increases the ingestion of C. perfringens endospores.

Clostridium perfringens toxin types

Action of C. perfringens exotoxins

Depending on the type these toxins are either produced alone or in combination, and are responsible for the various syndromes associated with this group of organisms. Note that beta toxin 2* is not produced by all strains, but is more often associated with intestinal disease. It is mainly associated with type A strains. The toxins cause disease as a consequence of their local effects on the intestinal tract and systemically due to absorbed toxins. The effects of these major toxins, also referred to as virulence factors, are divided into 2 groups:

• Alpha toxin, a phospholipase C, hydrolyses substances essential to the integrity of cellular membranes or other body structures. It is produced by all toxin types of C. perfringens
• Beta, Epsilon, Delta and NetB toxins act primarily on the vascular endothelium causing increased vascular permeability. Beta 1 toxin is inactivated by digestive enzymes and Epsilon toxin is produced by the bacteria as a protoxin which is cleaved by digestive enzymes to produce the active toxin. Thus disease due to Beta toxin is more common in neonates and that caused by Epsilon toxin is more common in older lambs. NetB is only found in strains of C. perfringens causing necrotic enteritis in poultry.

The different toxin types can be detected in 2 ways: 1) Direct detection in the sample of the relevant toxin using antigen detection tests such as the ELISA; 2) The detection of the genes in C. perfringens either in a sample or in a culture from the sample that encodes for the toxins.

Necrotic enteritis in chickens

Necrotic enteritis is a key disease of commercial broilers 2 to 6 weeks of age. It is mainly caused by C. perfringens type A, rarely type C.   Since antibiotics have been banned as growth promoters and there is decreased use of anticoccidials, like the ionophores, the prevalence of this disease has increased globally. The disease in chickens can be triggered by excessive dietary proteins and fats, especially if they are poorly digested. High numbers of coccidia, other pathogens and mycotoxins damage the intestinal epithelium leading to protein leakage and clostridial overgrowth. These co-infections assist in providing the necessary nutrients for this very rapidly growing bacterium. Although the function of the β-porin toxin NetB has not yet been fully unravelled, it is believed to work in the same way the C. perfringens Beta-toxin whereby the endothelium of blood vessels in the submucosa is targeted which leads to ischaemic necrosis of the mucosa, which in turn allows the C. perfringens to adhere to cells within the submucosa of the intestine. Severe, brown diarrhoea and a high mortality rate is the hallmark of acute disease. Subclinical disease results in poor nutrient absorption with decreased weight gain and poor feed conversion.

Enterotoxaemia, pulpy kidney, ‘overeating disease in sheep and goats (IMPORTANT)

Enterotoxaemia caused by C. perfringens Type D is common in recently weaned lambs (3 to 6 months of age) and young goats. This is the period when the passively acquired immunity is waning. Severe stress induced by handling, intestinal parasitism, and periods of starvation followed by overeating can result in the presence of undigested proteins in the large intestine.  The combination leads to clostridial overgrowth and retention in the large intestine. The bacteria produce various toxins, especially alphatoxin and epsilon protoxins, will lead to intestinal damage and increased absorption of these toxins. Epsilon protoxin is activated by cleavage of intestinal proteases such as trypsin will bind to endothelium of the intestine and once absorbed will affect the blood vessels of the rest of the body. This porin toxin will result in fluid and blood loss from the blood vessels as well as thrombosis. Tissues supplied by arterioles will develop an ischaemic necrosis. Tissues of the brain and kidneys are especially sensitive to the effects of the toxin. Post-mortem examination will therefore be typical of any septicaemic condition, with changes most noted in the heart, kidneys and brain. In older and partially immune lambs and kids i.e. those more than 6 months of age damage to the brain tissue, called focal symmetrical encephalomalacia (FSE) will lead to nervous disease. The so-called “dummies” or “staggers”.

Haemorrhagic enteritis in pigs

Neonatal piglets that have not received colostrum or are born from non-immune gilts/sows and are in faecally rich environments may develop a haemorrhagic diarrhoea or die suddenly. Mortality in litters can reach 100%. Full thickness necrosis and haemorrhages of the ileum and jejunum is noted. Clostridium perfringens type C is the primary cause.

Explain why Clostridioides difficile can occasionally cause enteritis in animals

Clostridioides difficile flourishes when other microflora in the large intestine are killed during antibiotic therapy. It can result in a pseudomembranous colitis  in humans, horses and dogs.  C. difficile and possibly C. perfringens Type A are considered causes of a severe, often fatal explosive diarrhoea known as “colitis X” in horses. Enterotoxin A and Cytotoxin B are responsible for the pathology. Antibiotics most associated with antibiotic-associated diarrhoea are broad-spectrum agents i.e. tetracyclines, fluoroquinolones, clindamycin (lincosamide) and broad-spectrum cephalosporins.

In humans, the hypervirulent and multi-drug resistant strain of Clostridium difficile B1/North American pulsed-field type 1 (NAP1)/ribotype 027 has caused outbreaks of colitis with increased severity, high relapse rate, and significant mortality in North America, Japan, Europe and Australia.

Diagnosis is by bacterial culture and toxin identification, Real Time PCR or by an ELISA to detect toxins A and B.

Treatment is only initiated in severe cases as mild cases will recover when treatment with the antibiotic that induced the disease was stopped. Antibiotics used to treat this condition in animals is metronidazole. Additionally, in humans glycopeptides can be used i.e. vancomycin or fidaxomycin. Drugs that slow intestinal motility should not be used. Other treatments include the use of cholesterol binders which bind to the toxins; antitoxins; and probiotics which include the ingestion of stool bacteria from a healthy relative. The disease can be prevented by avoiding the use of broad-spectrum antibiotics and by good sanitation within hospitals.

Histiotoxic clostridial infections

Clostridial infections of the liver 

Black disease/ infectious necrotic hepatitis

Clostridium novyi type B causes black disease or infectious necrotic hepatitis, principally in sheep and cattle, but occasionally in horses and pigs. This disease has been reported in Australia, New Zealand, United Kingdom, Europe and USA. Animals are infected by the ingestion of spores found on contaminated pastures, in utero, or via the umbilicus. The spores are phagocytosed by the monocyte-macrophage system in organs, such as the liver and spleen, where they remain as a latent infection until some tissue injury (i.e. migration tracts of immature liver flukes) provides the necessary local anoxic conditions to allow them to proliferate and result in toxaemia and death.

Bacillary haemoglobinuria

Clostridium haemolyticum (formerly C. novyi type D), which has been reported from the same geographical regions as C. novyi type B, is the cause a bacillary haemoglobinuria, an acute to peracute, highly fatal toxaemia of cattle and rarely of sheep, pigs and horses. The migration tracts of immature liver fluke result in liver damage, which provides conditions in which latent C. haemolyticum will germinate and produce beta toxin. This toxin causes further necrosis and intravascular haemolysis with the development of haemoglobinaemia, haemoglobinuria and  icterus. Bacteraemia and toxaemia result in collapse and death of the affected animal. The pathology of the disease is characterised by the presence of necrotic foci in the liver.

Tyzzer’s disease due to Clostridium piliforme.

Tyzzer’s disease is an enterohepatic disease of rodents and rabbits caused by Clostridium piliforme, an obligate intracellular pathogen. This hardy endospore former rarely infects the young of other mammals, such as foals and calves, causing a fatal hepatitis.  Histologically, focal areas of necrosis are seen in the liver that contain filamentous bacteria that are more easily detected with a silver stain. Infection of the intestinal tract is more common when the dams are fed nitrogen-rich feeds. Rabbits may develop the disease after treatment with sulphonamides. The disease is diagnosed by silver staining of affected tissues and PCR to detect C. piliforme gene sequences in affected tissues. The agent is difficult to eliminate in infected laboratory rodents and rabbits. Thus, it is best to euthanise the colony, disinfect the environment and start again with a C. piliforme free animals.

Gangrenous myositis

Blackquarter/Blackleg is a peracute or acute gangrenous myositis and associated cellulitis of cattle, caused by Clostridium chauvoei. Other clostridial agents that may cause similar lesions to that of Clostridium chauvoei are Clostridium novyi type A, Clostridium septicum and Clostridium sordelli. Clostridium novyi and C. septicum causes gangrenous lesions of the subcutis and muscles in sheep.  Clostridium perfringens type A contaminates wounds resulting in a gangrenous myositis (gas gangrene) or mastitis.

Bacterial endospores, found in faeces or carcass contaminated soils, enter wounds in the skin, mouth (periodonitis) or via dirty needles. Non-immune animals are susceptible to disease. Infections are more common in summer when the pastures are contaminated with mud containing the endospores. The endospores either act locally in damaged, anoxic tissue or are taken into the circulation and trapped in the small capillaries. Once tissue becomes damaged i.e. crush injuries and irritant injectable products the local tissue environment becomes more anaerobic. Damage to the large muscle groups is much more likely to lead to anaerobic conditions than other tissues. The dormant endospores will germinate and the bacteria divide rapidly. These proliferating bacteria will produce a variety of toxins dependent on infecting bacteria.

Exotoxins produced by the different clostridia causing gangrenous myositis

Clostridium chauvoei

• alpha toxin which is lethal, necrotising, and haemolytic.
• beta toxin behaves as a deoxyribonuclease
• gamma toxin which is a hylauronidase
• delta toxin which is an oxygen-labile haemolysin

Clostridium novyi type A

• alpha toxin which is necrotizing, cause oedema and lethal, endotheliotoxic
• gamma toxin which is a lecithinase or phospholipase C and is haemolytic and necrotising
• delta toxin which is a oxygen-labile haemolysin
• epsilon toxin which is a lipase

Clostridium septicum 

It is similar to C. chauvoei, but produces terminal spores, giving the bacterium a tennis racket-like morphology. Six different serotypes have been identified and four important exotoxins.

The exotoxins are:

• alpha toxin which is haemolytic, lethal and necrotizing
• beta l toxin which is a deoxyribonuclease
• gamma toxin which is a hyaluronidase
• delta toxin (septicolysin) which is haemolytic and cardiotoxic

The rapidly dividing bacteria and their toxins lead to further localised tissue necrosis, oedema and haemorrhage. Occasionally spores that lodge in the myocardium are stimulated, under the influence of cortisone, to induce tissue necrosis in the heart muscle. The toxins and occasionally the bacteria escape into the bloodstream resulting in septicaemia and death.

Clinical signs

The incubation period is short, between 1 to 3 days, and the course of the disease is short with death within 24 hours. Clinical signs if noticed include an early fever and swelling, crepitation and pitting oedema of the affected tissue. Lameness is sometimes noted.  Just before death the body temperature drops, some develop bloat, and they become recumbent and have increased heart and respiratory rates.

Pathology

The carcass of affected animals are usually congested and there may be haemorrhages present. Subcutaneous, intermuscular and other interstitial tissues in the vicinity of the affected musculature are distended by a yellow oedematous fluid which may be partially blood-stained and contain bubbles of gas. On cutting into an affected muscle, a reddish fluid exudes and there is a characteristic sweetish smell that resembles that of rancid butter. Although the large muscles of the hind limb are commonly affected, other muscles in the body, including the heart can also be affected.

Swelled head in rams and gangrenous myositis in sheep

Swelled head is an acute, infectious, but non‑contagious disease particularly of young rams that fight by head butting and is characterised by the development of a pronounced inflammatory oedema of the head and neck which develops following the infection of wounds often inflicted to the head during fighting. Infection of wounds by C. novyi type A probably takes place at the time of injury and results in rapid development of a severe subcutaneous inflammatory oedema with swelling of the affected part which often commences about the face and spreads to involve the whole head and neck. The swelling may be so severe as to interfere with respiration and cause snoring sounds. There may be exudation of fluid through the skin and closure of the eyes. The appetite is suppressed and the animal goes down and usually dies within 48‑72 hours after the onset of clinical signs.

Deep-seated injuries of the muscles i.e. dirty needles can result in gangrenous myositis. It is most often caused by Clostridium septicum. However, other clostridial species could be the cause.

With post-mortem examination, the skin and subcutaneous tissues of the head and neck, and the loose connective tissues of the peripharyngeal, perilaryngeal and peritracheal regions are extensively infiltrated with a clear, straw‑coloured inflammatory oedema that oozes from cuts made into the affected tissues and clots readily when exposed to the atmosphere. There are hydrothorax, hydropericardium and oedema of the lungs.

Post-parturient gas-gangrene

Post-parturient gangrene occurs in all ruminants but is more common in multiparous ewes that have had difficulties giving birth. Is usually caused by C. septicum. There is an incubation period of 12 – 24 hours after partus, with death after 12 – 24 hours after the onset of clinical signs. Clinical signs include fever, lethargy, straining and in some cows, a dark haemorrhagic discharge from the vulva. The vulva and perineum are usually severely swollen due to the presence of marked oedema and emphysema. Similar lesions occur in the genital tract with the uterus being atonic, red and emphysematous.

Gangrenous abomasitis in calves and lambs (braxy if caused by C. septicum)

Gangrenous abomasitis occurs sporadically in lambs, kids and calves. It is more common in temperate zones and is often associated with cold weather. It is usually caused by Clostridium septicum, occasionally C. perfringens type A. Acute abomasitis and abomasal ulceration followed by exotoxaemia/septicaemia and death.

Neurotoxic clostridial infections

Botulism

Botulism of all animals including humans is caused by the ingestion of preformed toxins from the obligate anaerobe C. botulinum and in rare cases, the cause is Clostridium butyricum and Clostridium baratii. The disease is more common in ruminants, horses, water birds and humans. Toxico-infection of the intestine and wounds are rare and have been recognised in horses and humans. Botulism is characterised by paresis or complete paralysis of most of the muscles.

There are nine different antigenically distinct toxigenic types of C. botulinum, designated A, B, C₁, C₂, C, D, E, F and G. Toxin types C and D are expressed by bacteriophages. In Australia, toxin D is the most common cause of botulism in ruminants. Botulism in water birds is also common. As the toxins are cytoplasmic proteins, they are only released when the bacterium dies. The botulism toxin is the most potent toxin known to produce intoxication in animals and humans.

Source of toxin

The organism is commonly found in soil, vegetation and occasionally in the intestinal contents of mammals, fish and birds. Vegetative cells multiply in putrefying material under anaerobic and warm conditions and produce exotoxin, which is released on autolysis of the bacterial cells. The most common sources of exotoxin include; carcass material, hay, moist haylage, silage, chicken litter, water or kitchen waste. Phosphate deficient vegetation/soils induces pica (bone craving/ osteophagia) causing ruminants to ingest bones, possibly containing toxin type D. In the Northern hemisphere, C. botulinum type B poisoning is more common in animals. A recent outbreak in horses in USA (late 2022 – early 2023) was associated with the ingestion of a particular brand of lucerne hay cubes.

Water temperatures together with decomposing vegetation and a high level of invertebrates in stagnant freshwaters allows C. botulinum to grow and produce toxin. The toxin is concentrated in invertebrates which in turn are eaten by water birds. Once the water birds start to die, the disease incidence increases as maggots feed off the carcasses, concentrate the toxin and are then eaten by healthy birds.

The toxins in human botulism cases have originated from canned meat, whale carcasses (Eskimos), fruit and vegetables = canning disease. 

Pathogenesis of botulism toxicity

Ingestion of preformed exotoxin, which is taken up by the digestive tract and disseminated in the blood. The toxin(s) bind irreversibly to the presynaptic terminal of cholinergic nerves, cleaves proteins essential for fusion and release of acetylcholine in synaptic vesicles at the neuromuscular junctions, thus preventing impulse transmission and the induction of muscle contraction. The C₂ toxin has the same outcome but works differently. It decreases synaptic membrane permeability. The effect of the toxin is dose related, with 1 g of toxin being able to kill 400 000 adult cattle. Once bound to nerve receptors it is unaffected by antitoxins. The result is a flaccid paralysis with death resulting from asphyxiation.

Toxico-infections or wound botulism (infection of the agent in the body with subsequent release of toxins) can occur especially in the gastrointestinal tract and via wounds. Stressed neonatal foals that develop gastric ulcers allowing entry of C. botulinum spores. The foals develop tremors and ataxia known as “shaker foal syndrome”. (A similar disease occurs in predominantly infants, known as “infant botulism”. Honey contaminated with spores is usually the most common source of the spores). Wound-related botulism in drug addicts is becoming more common but is very rare in animals.

Clinical signs of botulism

Incubation period of botulism varies but is generally between two to six days.

Disease course can be from peracute to chronic dependent on toxin dose and level of immunity. Typically in a group of animals, sudden deaths within a few days of ingestion, followed by animals suffering from an ascending paralysis (classical botulism).

The clinical signs of generalised botulism can include the following:

• Afebrile and fully alert. Some animals may appear aggressive. This is fear-associated as they cannot flee.
• Initially a hind limb weakness (loss in tone) with reluctance to stand.
• Tail paralysis.
• Advanced cases will lie on their sternum, then rest their heads on their flanks and eventually lie in lateral recumbency. Partial or complete paralysis of the muscles of locomotion, mastication and deglutination.
• Protrusion of tongue with loss of tone;
• Salivation and difficulty in chewing and swallowing can lead to dehydration.
• Bradycardia.
• Constipation due to ruminal and colonic stasis.

View these YouTube videos on botulism in a dog on day 1 [2:18] and day 4 [0:53], and this one showing the clinical signs of limberneck in a duck. [1:51]

In birds

Botulism is most common in water birds such as ducks. Typically healthy birds, affected birds, and dead birds in various stages of decay are commonly found in the same area. Birds are unable to use their wings and legs normally or control the 3rd eyelid, neck muscles, and other muscles. Birds with paralyzed neck muscles cannot hold their heads up (limber neck) and often drown. Death can also result from water deprivation, electrolyte imbalance, respiratory failure, or predation.

Pathology of botulism

There are no macroscopic lesions that can be regarded as characteristic of botulism. Animals may be dehydrated. Foreign bodies reflecting the presence of pica, such as bones, stones, bits of wood and pieces of iron, may be found in the rumen or reticulum in animals. Chronically affected animals may be constipated and have ruminal and colonic stasis.

Tetanus “Lockjaw”

Tetanus is a non-contagious, almost invariably fatal neuro-intoxication, particularly of horses and sheep, occasionally of cattle, goats, pigs and humans, and rarely of dogs and cats. The disease is caused by exotoxins of Clostridium tetani and usually develops after deep, penetrating wounds have been contaminated by the organism.

The endospores of C. tetani are found on an end of the bacterium, giving the bacterium a typical racket shape (terminal spores). They are present in soil, dust, and the faeces of most animals. The endospores of C. tetani are introduced into a wound from soil, faeces or other contaminated material. Typically deep wounds with a small entrance i.e. nail injuries, needles, dog and cat bites are susceptible to infection. The umbilicus, docked tail and scrotum contaminated with faeces are also prone to infection.

To find out more on tetanus in horses: Reichman P, Lisboa J, and Araujo RG (2008) ‘Tetanus in equids: A review of 76 cases’,  Journal of Equine Veterinary Science 28:518–523. doi:10.1016/j.jevs.2008.07.019

Endospores can remain dormant in wounds from months to years, before germinating and growing when conditions become favourable. Tissue necrosis and concurrent infection of wounds create a low reduction-oxidation (REDOX) potential locally, which predisposes to germination and growth of C. tetani. Actively dividing bacteria remain localised at the site of entry and produce tetanus toxin.

Tetanus toxin produced in wounds reaches the central nervous system, either through the lymph or bloodstream (most common), or by way of the peripheral nerves. The toxin enters the nervous system by endocytosis at the presynaptic terminals of motor axons and then ascends by retrograde intra-axonal transport to reach the anterior horns of the spinal cord from where it diffuses cranially.

View this excellent 7-minute YouTube animation video on the pathogenesis of tetanus. Be aware that a baby suffering from tetanus is shown at the beginning of the video. This can be disturbing to viewers.

Tetanus toxin acts on the central nervous system by presynaptic blockade of gamma-aminobutyric acid (GABA) or glycine release at inhibitory synapses on motor neurons. These effects result in a state of constant muscular spasticity and give rise to exaggerated responses to normally innocuous stimuli. Sustained spasm of the respiratory muscles eventually causes death by asphyxiation, cardiac arrest and general exhaustion. At a late stage of the intoxication, excitatory transmission is also inhibited.

The incubation period is between one to three weeks (three days to several months). The clinical signs are referable to a spastic paresis and include:

• Inability to eat.
• Increase in stiffness of voluntary muscles, followed by tetanic spasms of all muscles especially on external stimuli.
• Trismus, “Lock-jaw”, heads high, prolapse of the third eyelid.
• Wide stance “saw horse” with poor joint flexion.
• If startled, they fall down in lateral recumbency and go into spasms showing opisthotonos with the legs stiffened and outstretched.
• Hyperaesthesia, less marked in cattle.
• Colic (first sign in horses), constipation, sweating, dyspnoea, salivation, and urinary retention.
• Death usually follows within 12 – 72 hours.

Tetanus is a disease where you have to be able to observe the animal, its behaviours and movement. Thus looking at videos on animals with tetanus is by far the best way to remember it. Here are some YouTube videos of cases of tetanus in a horse [0:29] and a dog [1:39]. You will find many more.

Diagnosis of clostridial infections

The diagnosis of clostridial infections in animals is based on the following:

1. Young, unvaccinated animals that have been exposed to predisposing factors i.e. overeating or changes in eating habits in the case of enterotoxic infections; recent trauma in the case of histiotoxic infections; phosphate deficiency in botulism of ruminants.
2. Sudden onset or death without clinical signs in unvaccinated animals. Even though clostridial infections are not highly transmissible, groups of animals are often exposed to similar epidemiological factors. Note that clostridial infections can resemble acute toxicities.
3. Post-mortem examination with the presence of typical lesions in the case of enterotoxic and histiotoxic infections.
4. Fresh tissue samples and swabs can be used for either qPCR and anaerobic culture and bacterial identification. Note that samples must be collected and stored appropriately to be able to grow obligate anaerobes.

The diagnosis of clostridial infections can be a challenge:

1. The enterotoxigenic and histiotoxigenic clostridials are also putrefactive bacteria invading dead tissue and will decompose a carcass rapidly, so only freshly dead animals can be sampled.
2. The enterotoxins are rapidly broken down in the intestines, so intestinal contents should be freshly sampled and immediately frozen at -20ºC or lower.
3. Since the clinical signs are due to bacterial toxins, the bacterium is often only found at the site of infection or in the environment (botulism), so the sampling sites must be carefully selected.
4. The neurotoxins, especially botulinum toxin is very potent, so only small quantities are required to cause disease. Thus, the more sensitive the test, the more likely a diagnosis will be made i.e. mouse lethality test is more sensitive than the ELISA.
5. Most of the clostridial diseases are either peracute or acute manifesting before there is measurable antibody development. Thus serological tests detect immunity rather than clostridial disease.

Below is a table summarising the diagnosis of important clostridial diseases of animals.

Control (treatment, management and prevention) of clostridial diseases in animals

The bacteria causing clostridial diseases are common on farms and very serious when present. Thus, it is a case of prevention is better than cure. Prevention is done in one of two ways. Vaccination and control of the factors that predispose to disease i.e. avoid exposure, dietary and stress management. The clostridial multicomponent bacterin/toxoid vaccines are routinely used in cattle, sheep and goats in Australia.

With the exception of botulism which is an intoxication, all clostridial diseases can be treated with penicillin. In animals that are allergic to penicillins, tetracyclines or metronidazole can be used. If available, cases of botulism and tetanus can be treated with antitoxin or serum from hyperimmunised animals (usually horses). All other treatments are aimed at the relief of clinical signs.

END OF CHAPTER