zoonoses and communicable diseases common to ... - PAHO/WHO

212 BACTERIOSESBacteremia is present at the beginning of the disease. The fatality rate in untreatedcases is from 25% to 60%. At times, the disease may take the form of a mild, localized,and short-lived infection (pestis minor). Another, less frequent form is meningitis,which occurs primarily after ineffective treatment for bubonic plague (Butler,1988). In septicemic plague, nervous and cerebral symptoms develop extremely rapidly.Epistaxis, cutaneous petechiae, hematuria, and involuntary bowel movementsare seen. The course of the disease is very rapid, from one to three days, and casefatality may reach nearly 100%.Pneumonic plague may be a secondary form derived from the bubonic or septicemicforms by hematogenous dissemination, or it may be primary, produceddirectly by inhalation during contact with a pneumonic plague patient (primarypneumonic plague). In addition to the symptoms common to all forms, dyspnea,cough, and expectoration are present. The sputum may vary from watery and foamyto patently hemorrhagic. This is the most serious form.Primary pneumonic plague, the origin of which is human-to-human transmissionby aerosol and which has caused outbreaks and sometimes devastating epidemics,is rare. The pneumonic form seen in present times is the secondary form, resultingfrom septicemic dissemination. Since 1925, the US has recorded very few casesof primary pneumonic plague, all of which have resulted from exposure to a catwith secondary pneumonia. The first case occurred in California in 1980 (CDC,1982). A similar case occurred more recently in Arizona (CDC, 1992). In total,there have been three cases of primary pneumonia with the same characteristics.Secondary invasion of the lungs (secondary pneumonic plague) occurs in untreatedpatients and approximately 95% of them die without becoming transmitters ofthe agent by aerosol. If left untreated, the small number of patients who do not diemay give rise to other cases of pneumonic plague by airborne transmission (Polandand Barnes, 1979). In countries that maintain epidemiologic surveillance andwhere physicians and the general population are alert to the disease, the high fatalityrates caused by all forms of plague have been largely arrested by early diagnosisand prompt treatment with antibiotics, such as streptomycin, tetracycline, andchloramphenicol.The Disease in Animals: Y. pestis primarily infects animals of the orderRodentia; if affects wild as well as domestic rodents and, to a lesser degree, rabbitsand hares (lagomorphs). The infection may be acute, chronic, or inapparent.Different species of rodents and different populations of the same species showvarying degrees of susceptibility. In this regard, it has been observed that a populationin an enzootic area is more resistant than another in a plague-free area, a phenomenonattributed to natural selection. Domestic (commensal) rats are very susceptible;Rattus rattus die in large numbers during epizootics. By contrast,susceptibility varies greatly between different species in natural foci and must bedetermined for each situation. In the western United States, prairie dogs (Cynomysspp.) and the ground squirrel Citellus beecheyi are very susceptible, while certainspecies of Microtus or Peromyscus are resistant.Lesions found in susceptible animals dead from plague vary with the course of thedisease. In acute cases, hemorrhagic buboes and splenomegaly are present withoutother internal lesions; in subacute cases the buboes are caseous, and punctiformnecrotic foci are found in the spleen, liver, and lungs.