Mycoplasmas

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

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

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

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 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

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

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