Mycoplasmas

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BACTERIA



Overview

  • Pathogens belong to the Mycoplasma and Ureaplasma genera
  • Cause many diseases especially respiratory diseases of farm animals including contagious bovine pleuropneumonia
  • Can be involved in mastitis and conjunctivitis in cattle
  • Implicated in respiratory and urinary tract diseases in dogs and cats
  • Non-pathogenic mycoplasmas present in the rumen
  • Live on mucous membranes of oronasal cavity, conjunctiva and intestines
  • Stress factors and concurrent disease may predispose to tissue invasion
  • Usually host-specific
  • Limited survival in the environment


Characteristics

  • Smallest free-living prokaryotic organism
  • Pleomorphic organisms
  • Have no peptidoglycan cell wall
  • Susceptible to dessication, heat and disinfectants
  • Require enriched media containing animal protein, sterol and a source of DNA for growth
  • Colonies have a fried egg appearance
  • Most are facultative anaerobes


Pathogenesis and pathogenicity

  • Mycoplasmas adhere to host cells and produce toxins
  • Some adhere to neutrophils and macrophages and prevent phagocytosis
  • Mycoplasmas induce proliferation of macrophages and Monocytes - WikiBlood, and release of cytokines such as TNF and interleukins
  • Cause damage to cilia in the respiratory tract leading to pneumonia
  • Molecular mimicry allows some mycoplasmas to avoid the host immune response and may initiate immune-mediated disease


Diagnosis

  • Samples can be tested for the presence of mycoplasmas by fluorescent antibody techniques, peroxidase techniques and PCR
  • Biochemical profiles such as urease production can be used for identification
  • Ureaplasmas produce urease, whereas Mycoplasmas do not metabolise urea
  • Serolgy is required for specific identification including complement fixation tests, ELISA, agglutination tests and haemagglutination-inhibition tests
  • Growth inhibition tests using specific antisera can be used as well as fluorescent antibody tests


Contagious bovine pleuropneumonia

  • Contagious bovine pleuropneumonia is caused by M. mycoides subsp. mycoides small colony type
  • A severe contagious disease of cattle
  • Endemic in Africa, the Middle East and Asia
  • Aerosol transmission by close contact with clinically or subclinically affected animals
  • Severity depends on strain and host susceptibility
  • Slow spread of infection
  • 50% morbidity; mortality rate high in severe outbreaks
  • Large colony type causes pleuropneumonia, mastitis, septicaemia and polyarthritis
  • Clinical signs
    • Acute onset fever, anorexia, depression, lowered milk yield, hyperpnoea, coughing and a mucopurulent nasal discharge
    • Dyspnoea occurs with abducted elbows and extended necks and an expiratory grunt
    • Can be fatal within 1-3 weeks
    • Calves may suffer from arthritis, synovitis and endocarditis
  • Gross pathology
    • Marbled appearance to lungs with consolidated grey and red lobules separated by emphysematous areas
    • Serofibrinous pleural fluid
    • Necrotic foci surrounded by fibrous capsules in chronic cases act as source of infection
  • Diagnosis
    • Clinical signs and post-mortem appearance
    • PCR on pleural fluid, lung tissue, regional lymph nodes or bronchoalveolar lavage fluid
    • Fluorescent antibody test
    • Serological tests such as serum agglutination, haemagglutination, complement fixation, ELISA
  • Treatment and control
    • Slaughter of affected cattle in counries where the disease is exotic
    • Movement restrictions, quaranteen and slaughter of carrier animals in endemic countries
    • Vaccination in endemic regions


Mycoplasma bovis

  • Causes severe pneumonia in calves as a primary pathogen
  • Can occur secondarily to Pasteurella and Mannheimia and IBR
  • Associated with arthritis and mastitis
  • Mastitis associated with a severe drop in milk yield and a purulent discharge


Contagious agalactia of sheep and goats

  • Severe febrile disease of sheep and goats in parts of Europe, Africa, Asia
  • Caused by M. agalactiae
  • Mastitis, arthritis and conjunctivitis following parturition
  • Causes abortion
  • Fatal pneumonia in young animals
  • Shed in milk; localised in supramammary lymph nodes
  • Inactivated, attenuated vaccines available


Contagious caprine pleuropneumonia

  • Caused by M. capricolum subsp. capricolum'; occasionally M. mycoides subsp. capri or M. mycoides subsp. mycoides
  • Occurs in Africa and Turkey
  • Pneumonia, fibrinous pleurisy, pleural exudate, consolidated and emphysematous lungs
  • Aerosol transmission; highly contagious
  • Identified by growth inhibition disc tests
  • Inactivated vaccines available
  • M. mycoides subsp. 'mycoides causes septicaemia, pleuropneumonia, arthritis and mastitis in goats


Enzootic pneumonia of pigs

  • Enzootic pneumonia of pigs caused by M. hyopneumoniae
  • Occur in unfavourable conditions with poor ventilation, overcrowding and temperature fluctuations
  • Stunted growth rates, coughing and occasionally respiratory distress
  • Consolidation in apical and cardiac lung lobes
  • Immunofluorescence of lung tissue and complement fixation test or ELISA used for identification
  • Treatment includes in-feed antibiotics such as tylosin, lincomycin and tiamulin
  • Absent in specific-pathogen-free herds


M. hyorhinis and M. hyosynoviae of pigs

  • M. hyosynovia and M. hyorhinis produce syndromes similar to Glasser's disease with milder expression, rarely menigitis and arthritis
  • M. hyorhinis causes a chronic progressive polyserositis in pigs under 10 weeks old
  • A fever, laboured breathing, lameness and swollen joints occur
  • Serofibrinous pleurisy, pericarditis and peritonitis occur
  • Treatment includes tylosin and lincomycin
  • M. hyorhinis causes a polyarthritis in pigs of 10-30 weeks old, leading to transient lameness


Mycoplasmas of poultry

  • M. gallisepticum
    • Causes chronic repsiratory disease in chickens and infectious sinusitis in turkeys
    • Transmission via the egg and aerosol
    • Reduced egg production
    • Identification by serum plate agglutination test, haemagglutination inhibition and ELISA
    • Controlled in specific-pathogen-free flocks
    • Modified live vaccines and bacterins available
  • M. meleagridis
    • Hatching problems; airsacculitis in young poults; joint and bone deformities in growers; poor growth rates
    • Transmitted mainly via eggs and semen
    • Serum plate agglutination test for identification
    • In-water tylosin for first 10 days of life
    • Eggs can be dipped in tylosin
  • M synoviae
    • Causes infectious synovitis in chickens and turkeys
    • Transmitted by aerosol
    • Synovitis, arthritis, respiratory disease
    • Confirmation by isolation or serology
    • In-feed tetracycline
    • Eradication through specific-pathogen-free flocks


Other mycoplasmas