Dan C. Cavanaugh

The influence of climate on the seasonal prevalence of plague in the Republic of Vietnam.

An 8 year study of the influence of climate on the seasonal prevalence of bubonic plague in the Republic of Vietnam has been completed. Climatic conditions were found to influence the course of plague epidemics in 2 ways: 1) by regulating the density of the flea population; and, 2) by regulating the efficiency of Xenopsylla cheopis in transmitting the plague bacillus. Slight variations in temperature, relative humidity, and vapor pressure deficits either permit an epidemic to flourish or cause a decline in its intensity.

Stylostome formation by Leptotrombidium mites (Acari : Trombiculidae)

The modes of stylostome formation by larvae (chiggers) of Leptotrombidium intermedium, L. fletcheri, L. arenicola, and L. deliense in parasitized mouse skin were studied histologically in relation to their capacity to transmit Rickettsia tsutsugamushi. Three types of stylostome formation were recognized among the different species: the epidermal stylostome formed by the larva of L. intermedium; the mesenchymal stylostome formed by the larva of L. fletcheri; and, the mixed stylostome formed by the larva of both L. arenicola and L. deliense. Dermal inflammations related to the three types of stylostomes were histologically defined. The possible importance of stylostome characteristics to the transmission of rickettsial organisms is discussed.

SUSCEPTIBILITY OF RODENTS TO ORAL PLAGUE INFECTION: A MECHANISM FOR THE PERSISTENCE OF PLAGUE IN INTER-EPIDEMIC PERIODS

Oral infection of rodents with Pasteurella pestis has been demonstrated with both fully virulent and avirulent strains. Sustained rodent plague epizootics have been initiated and maintained in the absence of the classical flea vector. Transmission was due to cannibalism of the dying rodents by their healthy cagemates. Oral infection is considered to provide a plausible mechanism for the persistence of plague in an area where conditions are temporarily unsuitable for flea transmission.

Plague Toxin: its Effect in vitro and in vivo.

The murine toxin of Pasteurella pestis inhibited the respiration of heart mitochondria from the rat and the mouse but had little or no effect on the respiration of mitochondria from the rabbit, chimpanzee, dog, and monkey. Alterations occurred in tile S-T segments of the electrocardiogramus recorded corded from rats injected with � to 10 LD50 of toxin, but not in those from rats dying of hemorrhagic shock, hypoxia, intoxication with glucose, or Escherichia coli endotoxin. No abnormalities were observed in electrocardiograms from rabbits injected with large amounts of toxin.

Ecology of plague in Vietnam. I. Role of Suncus murinus.

Summary Pasteurella pestis was isolated from 7 Suncus murinus spleen pools and 3 flea pools obtained from it. Lesions indicating an acute infection were not observed in any of the 1,757 animals examined. When pooled sera were examined, 15 of 55 pools had titers of 1:16-1:256 against fraction I of P. pestis.

Differential Signs of Plague in Young and Old California Ground Squirrels (Spermophilus beecheyi)

California ground squirrels have been the source of many human cases of plague. The peak prevalence of plague in these squirrels usually occurs soon after the young of the year appear above ground, suggesting a high susceptibility in many of the young. Nevertheless, young squirrels exhibit high variability in their susceptibility to plague (Williams et al., 1979, J. Infect. Dis. 140: 618-621). Susceptibility to plague is greater in young than in old Asian ground squirrels, Citellus pygniaeus (Tinker and Kababukhov, 1934, Vestn. Mikrobiol. Epidemiob. Parazitol. 13: 299-303), C. fulvus and C. relictus (Lavrent’ ev, 1963, In Mateniaby Nauchnoy Konferentsii p0 Pnirodnoy Ochagovosti i Pnofilaktike Chumy, Afanas’yeva and Khurtselevskiy (eds.), Alma Ata, Kazakhstan, USSR, pp. 130-131). Studies done 40 yr ago with S. beecheyi considered age-related differences in susceptibility, but the data obtained were not convincing (Meyer, 1942, In MedicoSurgical Tributes to Harold Brunn, Univ. California Press, Berkeley, California, pp. 307-316). In recent studies, reported here, pathological signs of plague observed in young and old squirrels suggested that changes in susceptibility with age may also occur in S. beecheyi. Forty-six 3-mo-old S. beecheyi were collected in Monterey County, California, conditioned to the laboratory over 2 mo and inoculated with various doses of Yersinia pestis, as previously reported (Williams et al., 1979, op. cit.). Another six squirrels, collected with the

Serological Response of Rhesus Monkeys (Macaca mulatta) to Immunization and Infection with Pasteurella pestis

Summary Living attenuated Pasteurella pestis vaccine EV76(51f) was an effective immunizing agent for Macaca mulatta by either the oral or parenteral route. As determined by serological tests and challenge experiments, a killed plague vaccine was less effective.

Adiaspiromycosis in small Mammals of Viet Nam.

Adiaspiromycosis (Haplomycosis) is a widespread pulmonary infection of mammals caused by fungi of the genus Emi,tonsia. The etiologic agents, E. crescens Emmons & Jellison and E. parva (Emmons & Ashburn) Ciferri & Montemartini have been recovered or identified microscopically from the lungs of mammals collected on the continents of North and South America, Africa, Asia and Europe. These reports were reviewed in a recent publication (Taylor et al, 1967). During April and May, 1967, small rodents and insectivores were live-trapped as part of an epidemiological study of a plague epidemic in Nha Trang, Viet Nam. Lungs were removed from 324 animals, preserved in 70% ethyl alcohol, and transported to the SEATO Medical Research Laboratory where they were examined for microscopic evidence of Emmonsia infection. Lungs were maintained in alcohol for a period of 60 days to inactivate Pastenrella pestis and to reduce substantially air bubbles which confuse the search for adiaspores. The search for adiaspores was conducted according to a schema recommended by Jellison (personal colmmunication, 1967). Portions of each lung were sliced, about 3-5 mm thick, placed in a glass Petri dish, and digested in 2%, NaOH at room temperature. Each section was examined several times daily during the digestion of the tissue. Lungs from 324 animals were examined in this manner and adiaspores were detected in three. Microscopic sections were then prepared to

Decline of maternal antibodies to plague in Norway rats

The decline of maternal antibodies to the fraciton I antigen of Yersinia pestis was investigated in newly weaned Rattus norvegicus obtained from dams vaccinated with strain EV76(51F) of Y. pestis. IHA titre decreased by 50% each 7-3 days and CF titre declined 50% each 10-0 days in young rats. An analysis of available data indicated that maternal IHA and CF antibodies could persist to 3 months of age. Therefore, positive serologic reactions in young R. norvegicus, detected in the course of serological surveys, could be the result either of active immunization after exposure to the plague bacillus or of transient passive immunization (i.e. maternal antibody).