An outbreak of cat-associated Q fever in the United States

Q fever is usually acquired by contact with aerosols generated during parturition of domestic ungulates (e.g., sheep, cows, goats). In the maritime provinces of Canada, parturient cats have also been implicated in its transmission. A 66-year-old woman from eastern Maine developed high fever, rigors, headache, myalgias, pulmonary infiltrates, and elevated hepatocellular enzymes, and the diagnosis of acute Q fever was confirmed serologically. She and 14 other family members had attended a family reunion in Maine 2 weeks earlier, when they were exposed to a parturient cat. All 11 adults and older children attending the reunion developed symptoms consistent with acute Q fever. Serum samples were obtained from 10 who attended the reunion and 8 who did not attend. Titers greater than or equal to 1:64 to Coxiella burnetii were present in all who attended the reunion but in none of those who did not. Cat-associated Q fever should be considered when sporadic cases of the disease occur in the United States.

Epidemiology of rickettsial diseases

Rickettsial diseases have a diversity of epidemiologic characteristics reflective of the variety of ecologic situations in which the obligate intracellular bacteria are transmitted to humans. For the spotted fever group (SFG) rickettsiae, Rickettsia typhi, R. tsutsugamushi, Coxiella burnetii, and the human ehrlichial agent, humans are a dead-end host who plays no role in the maintenance of the organism in nature. All rickettsioses exist as zoonoses. Moreover, all rickettsiae are found in infected arthopods, which generally serve as the natural hosts and can transmit the infection to the next generation of ticks, mites, chiggers, or fleas. From our anthropocentric viewpoint, Q fever aerosol infection from parturient animals and Brill-Zinsser disease ignited epidemics of louse-borne epidemic typhus are exceptions. However, silent cycles of C. burnetii in ticks and R. prowazekii in the flying squirrel flea may have maintained these agents in transovarial or enzootic cycles for eons before humans and their domestic animals arrived on the scene. Thus, the epidemiology of rickettsial diseases must be recognized as an unfortunate aberration of the rickettsial economy. Several excellent reviews of rickettsial ecology contain a wealth of useful information.

Serologic diagnosis of human ehrlichiosis using two Ehrlichia canis isolates

Ehrlichia canis or a closely related rickettsial organism has been implicated serologically and morphologically as the causative agent of human ehrlichiosis in the United States. Although E. canis has been serially propagated in primary canine monocytes, only a limited quantity of antigen is obtained by this method. A continuous canine macrophage cell line, DH82, supports the growth of a new isolate of E. canis established from the whole blood of a carrier dog in Oklahoma. Serologic comparison of the Oklahoma isolate in the continuous canine cell line with a Florida isolate in commercial antigen slides revealed 100% specificity and 87.5% sensitivity.

Rabies

Human rabies is extremely rare and canine rabies is largely controlled in the United States. Wild animals are now responsible for most of the rabies prevention costs and postexposure treatments in the United States, either by direct exposure of humans or by exposure of domestic animals. Although the situation is similar in most other developed countries, canine rabies remains widespread and a substantial risk to persons traveling in developing countries, where millions of people are exposed and tens of thousands die of rabies each year. People living in the United States should be advised to avoid contact with wild animals and stray or ill-appearing domestic animals. Travelers to rabies enzootic countries can substantially reduce the risk of rabies exposures by avoiding all dogs as well as wild animals; those persons whose risk of exposure cannot be reduced should be educated about rabies and should receive preexposure vaccination.

Unexplained rabies in three immigrants in the United States. A virologic investigation

BACKGROUND

Extensive investigation of three patients who died of rabies in the United States failed to reveal any source of exposure to the disease. The three patients had immigrated to the United States from areas in Laos, the Philippines, and Mexico where rabies is endemic.

METHODS

We studied rabies viruses isolated from the three patients, other patients with a known source of exposure, and animals in the United States, Thailand (as a proxy for Laos), the Philippines, and Mexico. The viruses were characterized by indirect immunofluorescence and neutralization tests according to their reactions to panels of monoclonal antibodies. Transcribed complementary DNA from these isolates was amplified by the polymerase chain reaction; the DNA product was then analyzed by differential digestion with restriction enzymes.

RESULTS

The viral isolate from each of the three patients was a rabies variant with distinctive antigenic or genetic characteristics. For each of the three isolates, identical variants were found in specimens from rabid animals obtained from or near the country in which the patient lived before immigrating to the United States. None of these variants were found among the isolates collected from rabid animals in the United States.

CONCLUSIONS

Rabies infection in these three patients did not originate in the United States but resulted from exposures in Laos, the Philippines, and Mexico. Since the three patients had lived in the United States for 4 years, 6 years, and 11 months, our findings suggest that the onset of the clinical manifestations of rabies occurred after long incubation periods.

Rabies surveillance in the United States during 1989

In 1989, 4,808 cases of rabies in animals other than human beings were reported to the Centers for Disease Control, 1.8% more (4,724 to 4,808) than in 1988. Eighty-eight percent (4,224/4,808) of those affected were wild animals and 12% (584/4,808) were domestic animals. Cases were reported from 49 states, the District of Columbia, and Puerto Rico; Hawaii remained rabies-free. Skunks (1,657) continued to be the most commonly reported rabid wild animal. For the second consecutive year, more cats (212) were reported to be infected with rabies virus than any other domestic species. Compared with their 1988 reports, 5 states reported increases of greater than 100% (Alaska, 109%; New Jersey, 233%; Ohio, 133%; Oklahoma, 168%; and Washington, 125%), and 5 states reported decreases of greater than 50% (Connecticut, 63%; Mississippi, 56%; Montana, 67%; Nevada, 55%; and West Virginia, 53%) in 1989.

Epidemiologic, clinical, and laboratory findings of human ehrlichiosis in the United States, 1988

In 1988, the Centers for Disease Control and the Oklahoma State Department of Health identified 40 patients who had a fourfold or greater change in antibody titer in response to Ehrlichia canis. The median age of these patients was 42 years, 83% were male, 76% became ill between May and July, and 92% reported recent exposures to ticks. Patients resided in or were exposed to ticks in 14 states, including five where ehrlichiosis had not been reported before 1988. Thirty-four patients (85%) were hospitalized, and many had serious complications, including acute respiratory failure (seven patients), encephalopathy (six patients), and acute renal failure (four patients). Pulmonary infiltrates were demonstrated in 14 patients, cerebrospinal fluid pleocytosis was seen in 10 patients, and elevated levels of serum creatinine were demonstrated in eight patients. Two patients, both of whom had preexisting medical problems, died. Nonhospitalized patients received tetracycline therapy earlier in the course of their illness than hospitalized patients. There was no significant difference in the interval from initiation of antibiotic therapy to the first day of defervescence between patients treated with tetracyclines and those treated with chloramphenicol.

Epidemiologic factors, clinical findings, and vaccination status of rabies in cats and dogs in the United States in 1988. National Study Group on Rabies

Despite the availability of rabies vaccination through private veterinarians and government-sponsored rabies control programs, rabies was reported in an average of 338 cats and dogs per year from 1980 through 1987 in the United States. Information was collected on 90% of the 183 cats and 97% of the 119 dogs that were reported to have rabies in the continental United States in 1988. The median age of rabid cats and dogs was 1 year, and 81% were from rural areas. Compared with rabid cats, rabid dogs were more likely to have been male (66 vs 42%, odds ratio = 2.6), to have been kept as pets (84 vs 43%, odds ratio = 6.8), and to have had reported contact with wildlife before onset of illness (38 vs 14%, odds ratio = 3.8). Rabid cats accounted for a greater proportion of human rabies postexposure prophylaxis, bites to people, and exposures to other animals than did rabid dogs. Although the clinical signs of rabies varied, rabid cats were more likely than dogs to have had aggressive behavior (55 vs 31%, odds ratio = 2.8). In contrast, rabid dogs were more likely than cats to have had an illness consistent with a paralytic process. The median period between onset of illness and death was 3 days (range, less than 1 to 10) in rabid cats and dogs that were allowed to die of rabies. Vaccine failures were documented in 3 (1%) rabid animals (2 cats and 1 dog). All animals had received only a single dose of vaccine in their lifetime and were vaccinated when they were between 3 and 6 months old.

Diagnosis of human ehrlichiosis with the indirect fluorescent antibody test: kinetics and specificity

Human ehrlichiosis, an acute febrile illness caused by Ehrlichia canis or a closely related rickettsial organism, was first identified in 1986. From 1986 through 1988, sera from 85 patients demonstrated a fourfold rise or fall in antibody titer to E. canis. Seven (22%) of 32 patients initially tested during the first week after onset of illness. 17 (68%) of 25 tested during the second week, and all 18 tested during the third week had titers that exceeded the minimum positive titer of greater than or equal to 80. Of the 85 confirmed ehrlichiosis patients, 31 (36.5%) also had indirect fluorescent antibody titers considered diagnostic of infection with Rickettsia rickettsii, Rickettsia typhi, or Coxiella burnetti, but in most these diagnoses were not supported by epidemiologic, clinical, or serologic evidence. These results emphasize that patients suspected of having a tick-borne infection should be tested for antibodies to E. canis as well as for those to other rickettsiae.

Postexposure prophylaxis for rabies with antiserum and intradermal vaccination

The Thai Red Cross intradermal postexposure rabies treatment schedule was prospectively assessed in 100 Thai patients severely bitten by proven rabid animals. It consists of 0.1 ml of purified Vero cell rabies vaccine containing more than 2.5 IU of rabies antigen per 0.5 ml of reconstituted vaccine given intradermally at two sites on days 0, 3, and 7, followed by one 0.1 ml injection on days 30 and 90. The commercial vaccine used had an antigen content of 3.17 IU per 0.5 ml ampoule. Purified equine or human rabies immuno-globulin was also given on day 0 to patients with severe exposures. As much of the immunoglobulin as possible was infiltrated around the wounds. All patients were followed for 1 year post exposure. There were no deaths; the efficacy of the regimen was 100%. Antibody titre determination in a randomly selected subgroup showed seroconversion in all 10 patients.

Lack of correlation between human herpesvirus-6 infection and the course of human immunodeficiency virus infection

Human herpesvirus-6 (HHV-6) and human immunodeficiency virus (HIV) are both tropic for CD4+ lymphocytes. To determine whether HHV-6 infection affects the susceptibility to or the course of HIV infection, HHV-6 titers were measured by an anticomplement immunofluorescence assay in serum of three groups of homosexual or bisexual men: (1) those with AIDS (n = 78), (2) those with HIV-associated lymphadenopathy (LAS; n = 81), and (3) those who were HIV-seronegative (n = 55). Early and late serum samples were available for 45 men with LAS (median interval 49 months). Men with early LAS did not differ from HIV-seronegative men in either the percentage that were HHV-6-seropositive or in the distribution of titers. There was a significantly lower percentage of seropositives in AIDS patients than in the other two groups (P less than .01). LAS patients who progressed to AIDS did not differ in percentage seropositivity or distribution of titers from nonprogressors. HHV-6 titers tended to decrease over time. HHV-6 titers late in LAS were similar to those in AIDS patients. These findings suggest that it is unlikely that previous exposure to HHV-6 either predisposes to or affects the course of HIV infection.

Rabies prevention in Hawaii

The scientific basis of Hawaii's public health rabies prevention program is discussed, as is a proposed minor modification offered to assist Hawaii residents who use guide dogs and who want to travel out of state. Hawaii's current quarantine program has successfully prevented the introduction of the disease. Alternative programs involve risks that are not easily evaluated.

An epidemic of acute hemorrhagic conjunctivitis in American Samoa caused by coxsackievirus A24 variant

Between May 25 and July 5, 1986, an epidemic of acute hemorrhagic conjunctivitis affected an estimated 47% of the population on American Samoa. Coxsackievirus A24 variant was isolated from 18 of 22 patients. This is the first documented outbreak of acute hemorrhagic conjunctivitis due to coxsackievirus A24 variant outside of Southeast Asia and the Indian subcontinent. When this outbreak was compared with an outbreak on the island in 1981-1982 caused by enterovirus 70, conjunctival hemorrhage or injection and the severity of hemorrhage were less prevalent among cases in 1986, while upper respiratory and systemic symptoms were more common. Residents of traditional housing had significantly higher attack rates (48%) than residents of government housing (23%). Serum specimens collected from the residents of Samoa in 1985, before the outbreak, unexpectedly revealed the presence of neutralizing antibodies against coxsackievirus A24 variant. The presence of these antibodies correlated with protection against coxsackievirus A24 variant infection in this outbreak.

Human ehrlichiosis: prospective active surveillance in febrile hospitalized patients

Between 1 April 1987 and 30 September 1988 prospective active surveillance of human ehrlichiosis was conducted among febrile patients hospitalized in southeast Georgia. If disease of the immune system, bacterial infection, pneumonia, or surgical illness was documented by the end of the first full day of hospitalization, the patient was excluded. Of 75 patients enrolled in the study, 8 (10.7%) had a fourfold rise or fall in titer to Ehrlichia canis (case-patients). The rate was 5.3 cases/100,000 population. Case-patients were more likely than noncase patients to have become ill in May or June (P = .008) and to report a recent tick bite (P less than .001). At hospital admission, case-patients had lower white blood cell counts (median, 4,450/mm3; P = .001), platelet counts (median, 133,000/mm3 P less than .001), and higher aspartate aminotransferase (median, 68 IU/ml; P = .004) and alanine aminotransferase levels (median, 62 IU/ml; P = .038).

Human ehrlichiosis

Ehrlichiosis is one of the latest tick-borne illnesses to be reported in humans. The authors describe two cases of this rickettsial disease that were apparently acquired in Missouri. They discuss diagnosis and treatment.

Two-year comparative trial on the immunogenicity and adverse effects of purified chick embryo cell rabies vaccine for pre-exposure immunization

The human diploid cell rabies vaccine (HDCV) has been shown to be highly immunogenic when used for pre-exposure immunization. However, the high cost of the product and the adverse reactions seen following booster doses of HDCV have limited its use. A purified chick embryo cell (PCEC) rabies vaccine was compared with the HDCV by two routes of administration for reactogenicity, antibody response, duration of antibody, and anamestic response to boosters over a 2 year period. The study showed that the two vaccines were comparable in their immunogenicity and reactogenicity after initial three dose series. No adverse reactions were noted following the 2 year booster with PCEC. The PCEC can be produced at less than one-half the cost of the HDCV.

Human diploid cell rabies vaccine purified by zonal centrifugation: a controlled study of antibody response and side effects following primary and booster pre-exposure immunizations

Systemic allergic reactions following booster immunizations have complicated rabies pre-exposure prophylaxis with the human diploid cell rabies vaccine licensed in the US (conventional HDCV). We conducted two studies comparing an HDCV purified by zonal centrifugation to conventional HDCV. In a study of primary pre-exposure immunization, volunteers received one of four regimens: three 1.0-ml intramuscular (i.m.) or 0.1-ml intradermal (i.d.) doses of conventional or purified HDCV over 28 days. Although volunteers vaccinated i.m. had significantly greater rabies neutralizing antibody titres (VNA) 49 days, 91 days and 26 months after immunization began than volunteers vaccinated i.d. (p less than 0.005-p less than 0.05), there were no significant differences between vaccines. In a study of booster immunizations, 77 volunteers immunized with conventional HDCV 2 years earlier received a 0.1-ml i.d. booster with either conventional or purified HDCV. VNA was significantly greater with the conventional HDCV on days 7 and 28 after booster, but not on day 365. A moderate or severe reaction was reported by 5 (13%) of the 40 persons who received boosters with conventional HDCV, versus none of 37 who received the purified HDCV (p = 0.03). Purified HDCV appears to be preferable to conventional HDCV for booster vaccination.

Deterioration in immunologic status of human immunodeficiency virus (HIV)-infected homosexual men with lymphadenopathy: prognostic implications

Changes in immunologic parameters were followed in members of a cohort of human immunodeficiency virus (HIV)-positive homosexual or bisexual men with lymphadenopathy and were analyzed for differences between those who have and those who have not progressed to the acquired immunodeficiency syndrome (AIDS) (progressors, nonprogressors). T helpers and the Th/Ts ratio were lower in progressors than in nonprogressors both at entry into the study and at the latest visit. T suppressors were not different in the two groups at entry but were higher in nonprogressors at the latest visit. Evaluation of the patterns of change over time showed that T helpers and Th/Ts ratios tended to decrease over time in both nonprogressors and progressors, while T suppressors increased in nonprogressors and decreased in progressors. Although progressors had a greater deterioration in immunologic parameters over time, nonprogressors also had significant deterioration when compared with controls. Based on the respective percentages of men with abnormal or normal T helpers or Th/Ts ratio at entry who have already progressed to AIDS, we would conservatively estimate, considering their latest T helpers and Th/Ts ratio, that at least an additional 16 (32%) of our nonprogressors will develop AIDS in the next 5 years.

An outbreak of ehrlichiosis in members of an Army Reserve unit exposed to ticks

An outbreak of unexplained illness occurred in members of an army reserve unit after field training in an area of New Jersey endemic for Lyme disease. Nine (12%) of the 74 who attended the exercise had serological evidence of Ehrlichia infection, defined as a single rise in titer of antibody to Ehrlichia canis greater than or equal to 1:160 four weeks after training. Two reservists with early serum samples had documented seroconversion, defined by a four-fold or greater increase in titer of antibody to E. canis, with a peak titer of greater than or equal to 1:160. Reservists with serological evidence of Ehrlichia infection were more than three times as likely to report arthralgia, myalgia, headache, appetite loss, nausea, eye pain, and abdominal pain than the other reservists. No reservist with serological evidence of Ehrlichia infection was hospitalized and most had minimal or no symptoms. This outbreak of ehrlichiosis suggests that the usual symptoms of Ehrlichia infection are milder than previously reported and that ehrlichiosis must be considered in symptomatic persons with recent tick exposure.