Experimental Infection of Ectoparasitic Arthropods with Rickettsia Prowazekii (GvF-16 Strain) and Transmission to Flying Squirrels *

Abstract

Epizootiologic studies conducted during the past few years showed the existence of widespread natural infection of the southern flying squirrel, Glaucomys volans, with epidemic typhus rickettsiae, Rickettsia prowazekii. The ecological findings strongly implicated transmission of the etiologic agent by an arthropod vector. Studies were conducted under controlled laboratory conditions to determine whether ectoparasites naturally associated with flying squirrels (squirrel fleas, lice, mites and ticks) were capable of acquiring, maintaining and transmitting the infection. Also studied were the cat flea, oriental rat flea and the human body louse. Flying squirrels inoculated with the GvF-16 strain of R. prowazekii circulated rickettsiae in their blood for 2-3 weeks, thus providing ample opportunity for arthropods feeding on them to become infected. The results with Dermacentor variabilis ticks indicated that the rickettsiae did not consistently survive in this insect and were not passed to the eggs of adult females that had been infected subcuticularly. Mites became infected by feeding on infectious blood but failed to sustain the infection. Also, mites fed on an infected flying squirrel did not transmit the infection to a normal squirrel. Squirrel, cat, and oriental rat fleas readily became infected by feeding on a rickettsemic host or on infectious blood through membranes, but failed to transmit the infection to susceptible flying squirrels. In the studies with flying squirrel lice, however, transmission of epidemic typhus from infected to uninfected flying squirrels was demonstrated. Infection of the human body louse with the GvF-16 flying squirrel strain of R. prowazekii was similar to that previously observed with classical human strains, viz., multiplication of the rickettsiae and excretion in the feces.

Expression of the Rickettsia prowazekii pld or tlyC Gene in Salmonella enterica Serovar Typhimurium Mediates Phagosomal Escape

“…It is transmitted by the human-body louse Pediculus humanus corporis and is also associated with flying squirrels and their ectoparasites (9,11). Infected lice, when feeding, excrete a live, dormant form of the organism onto the cutaneous bite sites in their feces.…”

Cluster of Sylvatic Epidemic Typhus Cases Associated with Flying Squirrels, 2004–2006

“…The lack of detectable antibodies to R. prowazekii in household members of documented sylvatic typhus case-patients ( 6 , 8 ) has been used to support the hypothesis that risk for sylvatic typhus in the absence of direct exposure to flying squirrels and their nests is low ( 9 ) and thus may explain why human disease has been reported only sporadically. The cluster of cases described here suggests that where repeated and prolonged close exposure to flying squirrels and their nests occurs, potential for transmission can be high.…”

“…Later studies demonstrated serologic evidence of human R. prowazekii infection associated with flying squirrels in the eastern United States ( 1 , 3 , 4 ). Fleas and lice carried by the squirrels become naturally infected ( 1 , 5 , 6 ) and may be responsible for transmission ( 7 ); however, the exact mechanism of transmission remains unknown. From 1976 through 2002, a total of 41 cases of human R. prowazekii infection were documented in persons who had no reported contact with body lice or persons infested with lice ( 3 , 4 , 7 – 10 ).…”

Flying Squirrel–associated Typhus, United States

“…Various routes have been hypothesized, but none have been empirically established. Plausible mechanisms include inhalation or direct introduction (through mucous membrane or dermal abrasion) of infected feces from louse or flea ectoparasites of flying squirrels or through the bite of infected flea ectoparasites of flying squirrels ( 9 ). At least one species of flea ectoparasite ( Orchopeas howardii ) of flying squirrels is known to opportunistically bite humans and could serve as a bridge vector for transmission from flying squirrel to human.…”

“…At least one species of flea ectoparasite ( Orchopeas howardii ) of flying squirrels is known to opportunistically bite humans and could serve as a bridge vector for transmission from flying squirrel to human. Rickettsiae transmission among captive flying squirrels, however, has only been demonstrated with a louse vector ( 9 , 10 ). While the exact mechanism of pathogen transmission has not yet been determined, the lack of detectable exposure to R. prowazekii in the household members or co-workers of documented cases ( 3 , 5 ) supports the idea that the risk for R. prowazekii infection after casual or indirect exposure to flying squirrels is low.…”