The rickettsias associated with insects may be intracellular, epicellu-lar (living on the surface of cells), or extracellular; and they may have phoretic, mutualistic, or pathogenic relationships with their hosts. For example, Rochalimaea quintana (Schmincke), the causal agent of trench fever in man, grows extracellularly in the gut lumen of the human louse, Pediculus humanus. On the other hand, Rickettsia prowazekii da Rocha-Lima, the causal agent of typhus fever in man, is pathogenic to its vector, P. humanus. Rickettsias which are considered essential for development and reproduction of the host are Symbiotes lectularius in mycetomes of the common bedbug (Cimex lectularius) and Blattabacterium sp. in mycetocytes of cockroaches. Rickettsias belonging to the genus Rickettsiella are pathogenic to their insect hosts.
KeywordsHead Louse Cimex Lectularius Genus Symbiote Infected Insect Culex Pipiens
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