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Emerging Infections: Microbial Threats to Health in the United States
YARU, these samples subsequently yielded two isolates of a previously unknown arenavirus, a family of viruses generally thought to be rodent-borne. The organism was distinct from Lassa, Junin, and Machupo viruses, the other arenaviruses that are known to cause severe hemorrhagic illnesses in humans. The new agent has since been designated the Guanarito virus, and its associated disease has been labeled Venezuelan hemorrhagic fever (Salas et al., 1991).
Venezuelan health officials are now attempting to determine the risk factors, geographic distribution, and clinical spectrum of Guanarito virus infection and to update the incidence data on it. Studies are currently in progress at the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID) to develop an animal model for the disease and to evaluate possible therapeutic agents. In October 1991, scientists from YARU visited Venezuela to initiate a study to identify positively the rodent reservoir(s) of Guanarito virus.
Rodents have been implicated in a number of zoonotic infections, but the zoonotic pool also includes marine animals, such as seals, porpoises, and dolphins, which like humans are susceptible to outbreaks of infectious disease. Most such occurrences pass unnoticed, either because they occur far from shore or because the number of animals affected is too small to draw attention to the possibility of infectious disease. Occasionally, however, marine epidemics do attract attention, usually when large numbers of dead carcasses suddenly appear on a popular beach.
The most recent major epizootic, reported initially in harbor seals living in the waters off Europe and the United Kingdom, began in April 1988. Thousands of the animals died. The hardest-hit area was along Britain's East Anglian coast, where more than half of the native seal population is estimated to have died. The outbreak peaked in August and tapered off through late 1989. Few dead seals have since been reported in this area.
It now appears that the same or a similar disease was present in Siberian seals somewhat earlier than the European epizootic (Grachev et al., 1989). The disease was also found in porpoises (Kennedy et al., 1988) and in dolphins (M. Domingo et al., 1990). Extensive study of the European outbreak resulted in the isolation of the causative agent, a virus, which is similar to measles, canine distemper, and rinderpest viruses.
Occasionally, marine viruses cause disease in terrestrial mammals or humans. For example, a strain of influenza A virus (H7N7) led to epidemic outbreaks in seals in 1980 and caused conjunctivitis in humans who handled the affected seals (Webster et al., 1981). It has been suggested that vesicular exanthema of swine, a serious viral disease caused by a calicivirus, was introduced into pigs through feed that contained material from sea lions. Many caliciviruses of terrestrial mammals may have been introduced from marine sources (Smith and Boyt, 1990). Among human viruses, hepatitis E