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In 1981 and 1982, two US citizens died from Japanese encephalitis (JE) acquired in China. In 1983, the Centers for Disease Control initiated an evaluation of a purified, inactivated, mouse-brain-derived JE vaccine produced and used in Japan since 1966. Two doses of this vaccine given 1-2 weeks apart evoked neutralizing antibody titers greater than or equal to 8 in only 77% of recipients. After three JE vaccine doses administered 1-2 weeks apart, 99% developed titers greater than or equal to 8. When a third dose was given to 29 participants 6-12 months after the primary series, all developed titers greater than or equal to 16. Reported adverse reactions included injection site tenderness (18%), erythema (6%), or swelling (3%); headache (9%); and dizziness, fatigue, sleepiness, nausea, chills, fever, or lower back pain (less than or equal to 5%). On the basis of this study, three doses of BIKEN JE vaccine are recommended for US citizens who may be at risk of exposure to JE virus.

Using techniques of stereology, we measured the severity of lesions in ten cases of acute St Louis encephalitis (SLE) from the 1975 epidemic in northern Illinois. Percentage of fractional volume and numerical profile density on area (N/A) of cellular nodules and N/A of blood vessels with perivascular inflammatory cellular infiltration were significantly correlated in 17 anatomic regions of the CNS. Ranking of the severity of lesions in these regions agreed with subjective estimates of other cases of SLE. Immunofluorescent tests established the presence of SLE viral antigen in cell bodies of neurons. Our findings contribute to better understanding of the pathology of SLE in man.

More than half of the cases of plague in the United States are diagnosed in children. In the 1970s, 105 cases were reported, a 350% increase over the 1960s. Plague should be considered in the differential diagnosis of children from the western United States who have sepsis, especially those with lymphadenopathy. Complications of plague include meningitis, metabolic encephalopathy, abscess, and pneumonia. With appropriate treatment, prompt clinical response usually occurs. Careful isolation and epidemiologic investigation are essential to prevent the spread of the disease.

Twenty strains of Colorado tick fever (CTF) virus, isolated from ticks, mammals and humans, and two antigenic relatives of CTF virus were compared in cross-neutralization tests. Viruses were tested using single-inoculation sera prepared in hamsters. Antigenic variation, as measured by differences detected in the neutralization test, was noted among the virus isolates identified as strains of CTF virus. The virus strains isolated from humans appeared to vary the most in serological reactions. The two antigenic relatives of CTF virus are clearly distinct from strains of CTF and are different from each other. Antigenic relationships between these two viruses were established using two sets of single-inoculation antisera and both complement fixation and neutralization tests. Six distinct antigenic variants of CTF virus isolated from humans and the virus strain from ticks (75V1906) that showed the least antigenic variation, were tested against 49 coded serum pairs from clinically diagnosed cases of CTF. Significant differences were noted in the number of convalescent-phase sera that reacted with each virus strain and in the number of seroconversions observed with each test virus strain. Convalescent phase sera that reacted with multiple virus strains often varied significantly in antibody titre from one virus strain to another. This indicates that, in some instances, antibody was probably produced in response to infection by different antigenic variants of CTF virus.

During 1973 and 1974, we looked for cases of Colorado tick fever throughout Colorado; 228 cases were identified. Although 90% of the patients reported exposure to ticks before illness, only 52% were aware of an actual tick bite. Typical symptoms of fever, myalgia, and headache were common, but gastrointestinal symptoms were also prominent in 20% of the patients. Twenty percent were hospitalized; no deaths or permanent sequelae were noted. Persistent viremia (greater than or equal to 4 weeks) was found in about half of the cases; this finding was not associated with the occurrence of prolonged symptoms (greater than or equal to 3 weeks), which were also reported in half of the cases. One patient became reinfected with the virus. Increasing tourism in endemic areas and the frequent occurrence of prolonged or biphasic illnesses provide the potential for patients with Colorado tick fever to seek medical care anywhere in the United States.

An outbreak of seven cases of bubonic plague in New Mexico was investigated. Clinical features were studied and correlated with field studies in an attmept to determine the source of infection in patients with indefinite histories of exposure. Most patients presented with fever, malaise, and an acute painful lymphadenitis (bubo). One death occurred in a patient with bubonic-septicemic plague complicated by meningitis due to Yersinia pestis. All patients lived in rural or semirural areas, and most had been in the general vicinity of their usual residence during the six days prior to onset of symptoms. The outbreak was associated with probable epizootics in rodents in two different areas of the state. One case was traced to direct hand contact with plague-infected rabbits. One patient developed insect bites after sleeping in the same bed with a flea-infested cat. Three of the other five patients had insect bites, presumably flea bites, but none of the five recalled contact with rodents or rabbits. Four of the five, however, had been in contact with dogs or cats that were later shown to have titers of antibody to Y. pestis. These findings provide further support for the hypothesis that contact with domestic dogs and cats may result in direct or indirect transmission of Y. pestis to humans.

Meningitis caused by Yersinia pestis developed in 6 (6%) of a total of 105 patients with plague reported to the Centers for Disease Control from 1970 to 1979. Five of the six cases occurred in children aged 10 to 15 years. All six patients received antibiotic therapy before meningitis developed, which appeared between the 9th and 14th days after the onset of acute illness in five of the six patients. There were no neurologic sequelae. The antigenic and biochemical profiles of the Y pestis strains isolated from cerebrospinal fluid in the meningitis cases did not differ from those of the Y pestis strains obtained from blood and bubo aspirates in the other 99 patients, and neither did in vitro studies suggest antibiotic resistance. While plague meningitis is an uncommon complication of acute plague infection, physicians in the western United States should be aware that it may develop as much as 14 days after antibiotic therapy for the acute plague infection has been initiated.

Yersinia pestis, the etiologic agent of plague, is endemic in the western United States; 105 cases were reported between 1970 and 1979. Plague may manifest in one of three clinical forms; bubonic, septicemic, or pneumonic. Bubonic and septicemic plague represent relatively little risk for human-to-human transmission to contacts, although heavily infected secretions, such as drainage from a bubo, pose a theoretical risk, especially if they are aerosolized from a syringe during diagnohree clinical forms; bubonic, septicemic, or penumonic. Bubonic and septicemic plague represent relatively little risk for human-to-human transmission to contacts, although heavily infected secretions, such as drainage from a bubo, pose a theoretical risk, especially if they are aerosolized from a syringe during diagnohree clinical forms; bubonic, septicemic, or penumonic. Bubonic and septicemic plague represent relatively little risk for human-to-human transmission to contacts, although heavily infected secretions, such as drainage from a bubo, pose a theoretical risk, especially if they are aerosolized from a syringe during diagnostic aspirations. Pneumonic plague may be highly contagious to contacts and poses a greater risk. The Plague Branch, Center for Disease Control recommends that all patients with plague be placed in strict isolation for the first 48 hours of treatment because of the possibility that pneumonia may supervene. If it does not, wound and skin precautions are adequate for the duration of hospitalization. Untreated plague pneumonia is an epidemiologic emergency. All contacts must be identified promptly and those with face-to-face exposure should receive abortive antibiotic therapy. All contacts should be under surveillance, with twice-daily temperature checks, for seven days.

An outbreak of St. Louis encephalitis (SLE) resulted in 28 cases of the disease in Harris County, Texas, in 1986. The cases occurred principally in Baytown, in eastern Harris County, but five cases were also recognized in Houston. The risk of illness increased sharply with age, and all five fatal cases were in persons greater than 55 y. Case-control methods were used for the first time to study factors associated with the risk of acquiring SLE. Risk was associated with residences poorly sealed against mosquitoes (non-air-conditioned residences and those with inadequate screens). The number of hours spent outdoors and in outdoor activities, except sitting immediately outside residences, were not associated with risk. Our observations suggest that exposure to vector mosquitoes may have occurred indoors. No host factors were significantly associated with risk of acquiring SLE, but more cases were cigarette smokers and had family histories of hypertension or cerebrovascular disease.

Previous studies on the duration of antibody following vaccination with 17D yellow fever (17D YF) virus vaccine have indicated that immunity persists for at least 17 years and suggest that the vaccine may provide lifelong immunity. We studied sera obtained from 149 veterans of the Second World War, 30 - 35 years after military service during which YF vaccination was required for defined groups. A significantly high proportion of "vaccinated" subjects was found to be seropositive to 17D YF virus. The highest proportion of seropositive "vaccinated" veterans (97%) was among navy and air corps personnel, while only 60% of "vaccinated" army personnel and 19% of "unvaccinated" personnel were seropositive. This study suggests that (i) antibody to 17D YF virus, as measured by the plaque-reduction neutralization test (PRNT), persists for 30 years or more following administration of a potent vaccine; (ii) army personnel often had not received potent vaccine, even though their service history indicated that they should have been vaccinated; (iii) some personnel were vaccinated, although their service did not include vaccination-designated areas; and (iv) 88% of veterans with persistent PRNT antibody to 17D YF virus also had mouse-protective antibody against French neurotropic YF virus.

An epidemic of St. Louis encephalitis in 1985 in Mesa County, Colorado, led to 17 cases, including one fatality. Risk was associated with advanced age and residence in Grand Junction, the county's principal city. A trend was observed toward higher risk in females. However, increased risk in females was not associated with higher infection rates (increased exposure). Capture enzyme immunoassays detected specific immunoglobulin M (IgM) and immunoglobulin A after infection. A serosurvey of Grand Junction residents disclosed an infection rate of 4.0%, indicating that 1,123 epidemic St. Louis encephalitis infections may have occurred in the city. Evidence of previous St. Louis encephalitis virus infection was found in 11.2% of survey respondents who had neutralizing antibody to the virus without specific IgM. The prevalence of St. Louis encephalitis virus antibody was similar to rates observed in serosurveys undertaken 30 years earlier, indicating that the level of endemic St. Louis encephalitis transmission in the city had not changed appreciably in that interval.

Primary plague pneumonia occurred in a 47-year-old South Lake Tahoe woman shortly after face-to-face exposure to her plague pneumonia-infected cat. Both died. Field investigation revealed a recent plague epizootic in squirrels and chipmunks around the patient's home. Control measures included active surveillance and chemoprophylaxis of 197 contacts to the victim, a community alert on methods of self- and pet protection, and application of insecticide to reduce rodent flea populations. No secondary cases occurred.

An immunoglobulin M (IgM) capture enzyme immunoassay technique was adapted for the detection of antibody to Colorado tick fever virus in sera from 84 individuals for whom diagnosis had been confirmed by virus isolation or neutralization test. Titers were compared with those for IgG and neutralizing antibodies in these Colorado tick fever cases. IgM antibody titers were higher than neutralizing antibody titers, but neither appeared until 1 to 2 weeks after the onset of illness. Neutralizing antibodies were detected earlier than IgM antibodies, and both were detected with greater frequency than IgG antibodies. Late-convalescent-phase sera contained both neutralizing and IgG antibodies, but IgM was all but undetectable by 2 months after onset. Although the neutralization test may remain the serological test of choice, the enzyme immunoassay for IgM antibody offers a simple and more rapid method of serodiagnosis; the enzyme immunoassay is, however, less sensitive than the neutralization test. Furthermore, because there was a sharp decline in IgM antibody after 45 days, the presence of IgM antibody in a single serum sample provides a basis for the presumptive serodiagnosis of recent Colorado tick fever virus infection.