Pathogenesis

PATHOGENESIS

    • Adherence-, which is facilitated by the surface receptors of the host cell
    • Endocytosis
    • Phagosome destruction- Rickettsiae destroy the phagosomal mambrane by phospholipase
    • Multiply within the cytoplasm or in certain cases (spotted fever) nucleus.
  • Infection begins in the vascular system, organism proliferate in the endothelial and phagocytic cells and are disseminated via blood stream.
  • There is obstruction of small blood vessels because of hyperplasia of infected endothelial cells and resulting thrombi.
  • If capillary endothelium is affected, producing thrombi that result in haemorrhagic skin rashes.
  • Q fever organism has prediliction for mammary gland and placentae in cattle and sheep. Occasionally asymptomatic infections occur.
  • Q fever infection causes abortion in sheep, goats and cattle and bronchopneumonia in sheep.
  • Fever, hamorrhagic rash, stupor, shock and patchy gangrene of subcutis and skin are the common signs and lesions noticed in rickettsial infections
  • In case of Ehrlichiosis, the affected animals show symptoms of congested mucous membrane, purulent discharge from eyes and nose, gastritis, oedema of the hind legs and enlarged lymphnodes.
  • The mortality rate is 100% in acute cases. On P.M., the lesions are pulmonary oedema, haemorrhages of lung, hydrothorax, splenomegaly and hyperplasia of lymphnodes.
  • In Salmon poisoning, the mortality reaches 90%, affected dogs become weak, with vomition, depression and diarrhoea.
  • The important lesion is hyperplasia of lymphnodes with necrosis.

Steps involved in parasitization include

  • In mammals, by direct penetration of skin as a result of feeding by an infected arthropod (tick, louse, flea or mite)
  • In arthropods as the result of ingestion of blood of infected animals
  • From arthropod to progeny by infected ova.
  • In Q fever, wild animals such as bandicoot may constitute the primary reservoir, the infection being transmitted among them by Ixodes tick.
  • Transovarial transmission has been demonstrated in Ixodes tick. The rickettsiae are abundant in tick faeces and survive in them for long periods in the dry state.
  • Ticks transmit the disease to cattle, sheep and poultry. The rickettsiae are shed large numbers in the milk of infected cattle, uterine discharges, after-birth and other secretions.
  • The infected material gets dried up in the atmosphere and becomes suspended in the air and transported to long distances.
  • In human, the principal route of infection is mainly by inhalation of contaminated dust particle, ingestion of infected milk, and contact with contaminated material.
  • In Salmon poisoning in dogs, the disease is transmitted by eating raw salmon fish, which contained the infected fluke (Nanophytes salminicola).
  • Infected metacercariae encysted in the muscles of fish are ingested by dogs; flukes will get mature and release invasive rickettsiae.
  • The fluke eggs are passed in the dog intestine. These eggs develop into meracids, which infect the snail.
  • The cercaria develops within the snail and passes from snail and infects susceptible species of fish.
Last modified: Monday, 4 June 2012, 5:50 AM