Mycoplasmas

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

• Cause peritonitis in sheep and peritonitis in goats and peritonitis in pigs
• Enzootic pneumonia of pigs caused by M. hyopneumoniae and M. hyorhinis
• M. bovis, M. dispar and Ureaplasma in Enzootic pneumonia of calves
• May cause lymphocytic chronic inflammation (peribronchiolar and perialveolar cuffing).
• M. felis in mild respiratory infection
• M. ovipneumoniae in enzootic pneumonia of lambs
• M. hyosynovia and M. hyorhinis produce syndrome similar to Glasser's disease with milder expression, menigitis rare, arthritis most consistent