Rickettsia

Among the 17 named species of the Rickettsiaceae that have been documented to cause human illness, 5 are significant threats of a fatal outcome, namely Rickettsia rickettsii, Rickettsia prowazekii, Orientia tsutsugamushi, Rickettsia typhi, and Rickettsia conorii. These Rickettsia can be obtained in nature, propagated by available methods, and prepared in a stable state of infectivity by a low dose. Thus, they could be used by terrorists. After a series of attacks, the public would seek to receive a protective vaccine. Rocky Mountain spotted fever, louse-borne typhus, and scrub typhus are currently reemerging infectious diseases with increasing incidence. Epidemic louse-borne typhus requires a vaccine to control large epidemics that occur in association with natural and manmade disasters including wars. The vast majority of emerging rickettsial diseases have existed for eons, are seldom life threatening, and were only discovered recently: African tick bite fever (Rickettsia africae), Flinders Island spotted fever (Rickettsia honei), Japanese spotted fever (Rickettsia japonica), tick-borne lymphadenopathy (Rickettsia slovaca), maculatum spotted fever (Rickettsia parkeri), flea-borne spotted fever (Rickettsia felis), the unnamed eschar-associated infections (Rickettsia aeschlimannii and Rickettsia massiliae), and the unnamed infection caused by Rickettsia monacensis. Other rickettsioses (North Asian tick typhus, Rickettsia sibirica; Queensland tick typhus, Rickettsia australis; rickettsialpox, Rickettsia akari) are rarely severe illnesses. A vaccine should be developed against R. prowazekii and would likely provide good crossprotection against R. typhi. Because R. rickettsii is the most virulent Rickettsia and genetic engineering to complete antibiotic resistance is highly feasible, development of a vaccine against Rocky Mountain spotted fever would be a very wise biodefense strategy. Such a vaccine would very likely provide crossprotection against other spotted fever group rickettsiae. The preparation of a vaccine that protects against all Rickettsia species is a genuine possibility. Such a vaccine would have a commercial value for use in travelers, especially those going on safari in southern Africa, where more hunters and tourists suffer from African tick bite fever than malaria. Development of a vaccine that is protective against scrub typhus poses tremendous challenges owing to transient active immunity and vast antigenic diversity of the agent.