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Small mammals were livetrapped during 12 months in crop fields and weedy borders at 18 sites in central Argentina. A total of 1,652 mammals of 14 species was captured during 33,060 trap-nights. Six species of rodents comprised >95% of captures. Periodically disturbed fields of crops were dominated by Calomys musculinus and C. laucha, and to a lesser extent Mus musculus. A second group composed of Akodon azarae, Bolomys obscurus, and Oligoryzomys flavescens primarily inhabited the more stable, weedy borders of cultivated fields. Peaks in relative densities of C. musculinus, C. laucha, and M. musculus were observed in summer and early autumn, and populations declined to low numbers in winter, following harvest. In contrast, maxima for A. azarae, B. obscurus, and 0. flavescens were in late autumn and early winter, and numbers never declined to low values seen for the other species. These characteristic differences in habitat associations and relative densities of pampas rodents may reflect colonizing potential, as both Calomys and Mus potentially are highly opportunistic genera. The common rodent species of the central Argentine pampas show distinct habitat associations, interspecific interactions, and reproductive rates. Akodon azarae and Bolomys obscurus, for example, are found predominantly in more stable linear habitats (fencerows, roadsides, and railroad rights-of-way), and may be behaviorally dominant over the two species of Calomys (de Villafanie et al., 1977; Kravetz, 1977). Species of Calomys frequently are numerically dominant in cultivated fields and have been described as better colonizers than Akodon and Bolomys by virtue of larger litter size, reproduction at younger age, and high frequency of postpartum estrus (de Villafanie et al., 1977). Interspecific interactions and seasonal changes in suitability of habitats may result in different patterns in population processes among rodent species that inhabit the pampas. Four of >10 species of rodents present (C. musculinus, C. laucha, A. azarae, and Mus musculus) were implicated as hosts of Junin virus, etiologic agent of Argentine hemorrhagic fever (Sabattini and Contigiani, 1982; Sabattini et al., 1977), a serious viral disease infecting humans in a small area in southern Santa Fe and C6rdoba, and northern Buenos Aires and La Pampa provinces. As a consequence, many ecological studies during the past 30 years were directed toward understanding and controlling the rodent reservoir of this disease. In crop fields, lower densities of rodents were found in soybeans than in corn (Busch et al., 1984; Maiztegui et al., 1986), suggesting that reducing cultivation of corn in favor of soybean production would decrease populations of rodents. Further, as a correlation was observed between high densities of rodents in corn fields and high incidence of Argentine hemorrhagic fever (Instituto de Virologia de C6rdoba, 1966; Sabattini and Maiztegui, 1970), this change of cultivation practices also may lead to lower incidence of the disease (Busch et al., 1984). A model of ...

Argentine hemorrhagic fever (AHF), caused by the arenavirus Junin, is a major public health problem among agricultural workers in Argentina. A prospective, randomized, double-blind, placebo-controlled, efficacy trial of Candid 1, a live attenuated Junin virus vaccine, was conducted over two consecutive epidemic seasons among 6500 male agricultural workers in the AHF-endemic region. Twenty-three men developed laboratory-confirmed AHF during the study; 22 received placebo and 1 received vaccine (vaccine efficacy 95%; 95% confidence interval [CI], 82%-99%). Three additional subjects in each group developed laboratory-confirmed Junin virus infection associated with mild illnesses that did not fulfill the clinical case definition for AHF, yielding a protective efficacy for prevention of any illness associated with Junin virus infection of 84% (95% CI, 60%-94%). No serious adverse events were attributed to vaccination. Candid 1, the first vaccine for the prevention of illness caused by an arenavirus, is safe and highly efficacious.

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During an outbreak of type E foodborne botulism in Cairo in 1991, an investigational equine F(ab')2 "despeciated" heptavalent botulism immune globulin (dBIG) was provided to the Egyptian Ministry of Health by the U.S. Army. Of 54 patients known to have been treated with antitoxins, 4 received commercially available trivalent antitoxins, 45 received dBIG, and 5 received both commercial antitoxin and dBIG. Physicians recorded side effects in 10 (22%) of 45 patients who received dBIG; in nine cases, reactions were considered "mild," and in one case they were believed to be serum sickness. In contrast, possible serum sickness during hospitalization was recorded for two of four patients who were receiving commercial antitoxins. No complications of therapy were noted for any patient who was receiving both antitoxin types. In a separate study, 31 patients were contacted about their reactions to the antitoxin by telephone after discharge from the hospital. Seven (54%) of 13 patients attributed symptoms that they experienced while they were hospitalized to receipt of dBIG, while four (44%) of nine patients who indicated that they had received commercial antitoxins and one (20%) of five who received both commercial antitoxin and dBIG reported side effects before discharge. Data on the efficacy of the antitoxins were not obtained. In our experience, equine dBIG was at least as safe as commercially available antitoxins in treating type E foodborne botulism.

Junin virus-infected rhesus macaques received prophylactic and therapeutic ribavirin to assess the potential of this drug for treating humans with Argentine hemorrhagic fever. When ribavirin was administered intramuscularly at the time of experimental infection with the lethal P3790 strain of Junin virus, all animals were protected from clinical disease. A delay in the initiation of therapy until after the onset of illness resulted in improvement and resolution of systemic signs of disease; however, survivors subsequently developed a late-onset central nervous system infection which was fatal in two of three animals. Side effects of ribavirin included thrombocytosis and severe anemia, both of which resolved promptly on withdrawal of drug therapy. Results of this study suggest that ribavirin may prove useful in treating humans with Argentine hemorrhagic fever.

Argentine hemorrhagic fever (AHF) is a potentially lethal infection in Argentina. The case-fatality ratio is >15%, but treatment reduces the mortality rate to <1%. Diagnosis is based on clinical and laboratory criteria, but no case definition has been validated. A chart review was conducted for patients hospitalized with suspected AHF. Individuals with a fourfold rise in antibody titer were classified as cases. The combination of a platelet count of <100,000/mm3 and a white blood cell (WBC) count of <2,500/mm3 had a sensitivity and specificity of 87% and 88%, respectively, thus suggesting that the use of these criteria in a case definition would be helpful for epidemiological studies of AHF. The combination of a platelet count of <100,000/mm3 and a WBC count of <4,000/mm3 had a sensitivity of 100% and a specificity of 71%; the use of these criteria in a case definition should be helpful for screening patients for therapy with immune plasma in the region where AHF is endemic.