Mycoplasmas

From WikiVet English
Jump to navigation Jump to search


Infectious agents and parasitesWikiBugs Banner.png
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, 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
  • 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
  • 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