|
Overview
- Mainly pathogens of farm animals
- Commensals of mucosa of upper respiratory tract and oral cavity
- Cannot survive long in the environment, therefore carrier animals are important in their transmission
- Cause granulomatous inflammation
Actinobacillus characteristics
- Small Gram negative coccobacilli
- Oxidase negative
- Do not grow on MacConkey
- Non-motile
- Facultative anaerobes which ferment carbohydrates to produce acid
Actinobacillus lignieresii
- Pathogenesis and pathogenicity:
- Commensal in the mouth and intestinal tract of cattle and sheep
- Penetrates damaged mucosa to cause chronic granulomatous inflammation of soft tissues, a condition known as Actinobacillosis
- Enodogenous, sporadic infection
- Lesions in the tongue, cheek, lips and sometimes in the lower gut and lungs from aspiration
- Often spreads from the site of infection to lymphatics, and may cause pyogranulomatous lymphadenitis
- Myositis and formation of fibrous tissue in the lesions lead to hardening of the tissue, hence the condition is known as 'wooden tongue' in cattle
- In sheep abscesses with thick walls are produced
- Feeding is impaired, causing loss of condition
- Infection in the oesophageal groove can cause tympany and enlargement of the retropharyngeal lymph node, causing difficulty in swallowing and breathing
- Cutaneous lesions in cattle and sheep
- Contamination of the environment via ulcerating lesions
- Diagnosis:
- Induration of tongue
- Tissue sections may demonstrate pyogranulomatous foci containing club colonies
- Gram negative rods may be present in smears from exudates
- Cultures on blood agar and MacConkey agar, incubated for 24-72 hours
- Blood agar: small, sticky, non-haemolytic clonies
- MacConkey agar: slow lactose fermentation
- Treatment:
- Sodium iodide parenterally, or potassium iodide orally
- Potentiated sulphonamides or a penicillin/streptomycin combination
- Rough feed should be avoided
Actinobacillus pleuropneumoniae
- Contagious porcine pleuropneumonia especially of pigs under 6 months
- Endemic in UK
- 12 serotypes causing the same disease
- Different serotypes in different regions, with serotypes 3,6 and 8 the most common in the UK
- Pathogenesis and pathogenicity:
- Virulent strains possess capsules which are antiphagocytic and immunogenic
- Fimbriae allow the bacteria to attach to cells of the respiratory tract
- Damaged neutrophils in the lungs produce lytic enzymes
- The sustained inflammatory response causes tissue necrosis
- Lungs consolidated and necrotic with fibrinous pleuisy at post mortem
- Produce three cytotoxins which belong to the repeats-in-structural-toxin (RTX) cytolysin family
- RTX toxins:
- Several peptide repeats within the molecules
- Produced by various Gram-negative bacteria
- Possess four contiguous genes, A, B, C and D
- A is the structural gene; B and D are required for secretion; C allows post-translational activation of the gene product of A into a functional product
- ApxI is a strong haemolysin with cytolytic activity
- ApxII is a weak haemolysin
- ApxIII is a cytotoxin
- Different Actinobacillus pleuropneumonia serotypes secrete a particular combination of toxins; American serotypes secrete ApxI and II; European serotypes secrete ApxII and III
- Toxins introduce pores into cell membranes
- Clinical signs and epidemiology:
- Acute disease in susceptible herds with high morbidity and mortality (up to 50%)
- In acute outbreaks, pigs may be dyspnoeic, pyrexic or anorexic
- Blood-stained froth surrounding nose and mouth
- Cyanosis
- Pregnant sows abort
- Causes pneumonia in pigs
- Carrier herds have some immunity, protecting from acute disease, where lesions are often subclinical, and deaths sporadic
- Lung scarring and pleural adhesions in many recovered animals
- Solid immunity develops in recovered animals to all serotypes
- The disease is spread between herds by carrier pigs
- Diagnosis:
- Haemorrhagic consolidation close to the main bronchi and fibrinous pleuritis may be suggestive
- Specimens are cultured on chocolate agar and blood agar in 5-10% carbon dioxide for 2-3 days
- Small colonies surrounded by clear haemolysis
- No growth on MacConkey agar
- Positive CAMP reaction with Staphylococcus aureus
- Most strains are NAD-dependent (grow on Heated Blood agar)
- Immunofluorescent- or PCR-based techniques
- The bacteria on the palatine tonsil may remain undetected by serological tests and swabbing, and can therefore cause an outbreak in naive pigs
- Treatment:
- Antibiotics depending on the strain of bacteria
- Prophylactic antibiotics for in-contact pigs
- Control:
- Killed and polyvalent bacterin vaccines as well as a subunit vaccine are available
- Improve ventilation, avoid chilling and overcrowding
Actinobacillus equuli
- Commensal of the equine intestinal and reproductive tract
- Pathogenesis and clinical signs:
- Foals infected in utero or or after birth via the umbilicus
- Infection at birth causes severe enteritis and septicaemia within 24 hours, known as sleepy foal disease
- Foals become pyrexic and recumbent
- Death usually occurs within 1-2 days
- In foals that survive neonatal infection the condition progresses to cause joint infections and purulent nephritis, enteritis or pneumonia
- A. equuli in arthritis of horses
- Abortion, septicaemia and peritonitis in horses
- Diagnosis:
- Specimens cultured on blood agar and MacConkey agar and incubated aerobically for 1-3 days
- Sticky colonies with variable haemolysis on blood agar
- Lactose-fermenting colonies on MacConkey agar
- Treatment and control:
- Antimicrobials ineffective unless early in course of disease
- Blood trasfusion and administration of colostrum
- Good hygiene
- Consider prophylactic antibiotics for new-born foals
- Bacteria susceptible to streptomycin, tetracyclines and ampicillin
- In other animals:
- Septicaemia in piglets
- Arthritis and enteritis in pigs
- Enteritis in calves
- RTX group cytotoxin present
Actinobacillus suis
- May be present in upper respiratory tract of sows
- Pathogenicity and clinical signs:
- Infection of piglets via aerosol or possibly skin abrasions
- Fatal septicaemia in piglets 1-8 weeks old
- Mortality up to 50% in some litters
- Fever, respiratory distress, prostration and paddling of forelimbs seen in piglets
- Petechial and ecchymotic haemorrhages in many organs
- Interstitial pneumonia, pleuritis, meningoencephalitis, myocarditis and arthritis
- Causes abscesses in joints and lungs of older pigs
- Carried in the nasopharynx of pigs and nose of horses
- Carriage may confer immunity to the more severe pleuropneumonia
- Diagnosis:
- Specimens cultured on blood agar and MacConkey agar for 1-3 days
- Sticky haemolytic colonies
- Pink, lactose-fermenting colonies on MacConkey agar
- Treatment and control:
- Bacteria usually susceptible to ampicillin, carbenicillin, potentiated sulphonamides and tetracyclines
- Disinfect contaminated pens
- Other animals:
- Septicaemia and pneumonia in foals
- Pneumonia in pigs and horses
Actinobacillus seminis
- Epididymitis in young rams (4-8 months)
- Polyarthritis in lambs
- Organism found in prepuce
- Opportunistic infection causing abscesses in epididymides
- May be purulent discharge onto scrotal skin
- Specimens cultured on blood agar and incubated aerobically for 1-3 days produce pin-point haemolytic colonies which are catalase-positive; no growth on MacConkey agar
Actinobacillus actinomycetemcomitans
- Epididymitis in rams