Special Veterinary Pathology

General pathology of mycoplasmal, chlamydial and rickettsial infections

MYCOPLASMAL, CHLAMYDIAL AND  RICKETTSIAL INFECTIONS

Mycoplasmal infections

• Mycoplasma are the smallest free – living microbes, 300 – 800 mm in diameter
• They have no cell wall but bound by plasma membrane
• Mostly host specific
• Colonise mucosal surfaces and are non – invasive
• Spreads by aerosol (droplet injection), venereal (sexually transmitted) or inutero

Rickettsial infections

• Minute, Gram – negative, obligate intracellular parasite
• Multiply only within cells
• Transmitted from one species to other by arthropod vectors in which transovarian transmission is common
• Rickettsia species have an affinity for growth in endothetial cells and vascular smooth muscle cells
• Vasculitis complicated by thrombi and haemorrhages

Chlamydial infections

• Chlamydial organisms multiply only within the host cells
• Non – motile, spherical, Gram – negative and have cell wall
• Two different forms by Chlamydia
• Elementary body (EB)
• Reticulate body (RB)
• Elementary body never divides but attaches to host cell and gains entry
• Reticular body is intracellular, metabolically active non – infectious form and divides by binary fission

Developmental cycle of chlamydia

• Attachment and penetration by elementary body
• Transition of metabolically inert EB into active reticulate body
• Multiplication of the reticulate body by binary fission producing many progeny
• Maturation of non – infectious reticulate bodies into infectious bodies
• Special staining technique for demonstration of Chlamydia is Macchiavello – Red ; Castaneda – Blue; Dark purple with Giemsa
• Wet mounts, phase contrast microscopy