Seroepidemiology of infections due to spotted fever group rickettsiae and Ehrlichia species in military personnel exposed in areas of the United States where such infections are endemic

A prospective, seroepidemiologic study of spotted fever group rickettsiae (SFGR) and Ehrlichia infections was done among 1194 US military personnel exposed in a heavily tick-infested area of Arkansas in 1990. Seroconversion (4-fold) and seroprevalence rates were determined by indirect immunofluorescent antibody assays. Seroconversions to SFGR occurred in 30 persons (2.5%), whereas seroconversion to Ehrlichia species occurred in 15 (1.3%). The majority of seroconverters did not report symptoms (22/30 [73%] of SFGR seroconverters; 10/15 [67%] of Ehrlichia species seroconverters). History of tick attachment was associated with seroconversion to SFGR (relative risk [RR] = 4.3, P < .001) and Ehrlichia species (RR = 3.6, P < .05). Use of permethrin-impregnated uniforms significantly decreased risk of infection (P < .01); use of bed nets increased risk by 4-fold. Tickborne infections represent a significant threat to military personnel training in areas in which these infections are endemic.

National surveillance for Rocky Mountain spotted fever, 1981-1992: epidemiologic summary and evaluation of risk factors for fatal outcome

Between 1981 and 1992, the Centers for Disease Control collected and summarized 9,223 cases of Rocky Mountain spotted fever (RMSF) reported from 46 states. Four states (North Carolina, Oklahoma, Tennessee, and South Carolina) accounted for 48% of the reports. The annual incidence per million U.S. population decreased from a high in 1981 of 5.2 to a low in 1992 of 2.0, primarily due to decreased incidence in the southeast. Case report forms were filed on 7,650 patients, of whom 4,217 had laboratory-confirmed RMSF. The age group with the highest incidence was those 5-9 years of age. Most cases (90.0%) occurred between April 1 and September 30 and included a history of tick attachment (59.6%). Reported symptoms included fever (94.0%), headache (86.2%), myalgia (82.5%), and rash (80.2%). The case-fatality ratio was 4.0%. Risk factors associated with death included older age, delay in treatment or no treatment, and treatment with chloramphenicol (compared with tetracycline); however, insufficient data existed to fully assess the confounding effect of severity of illness on antibiotic choice.

Immunogenicity of rabies vaccines used during an urban epizootic of rabies in Mexico

From 1 July 1987 to 31 December 1988, 30% of 247 rabid dogs in Hermosillo, Mexico had a positive history of rabies vaccination. Serosurveys suggested that inactivated suckling mouse brain vaccine (INACT-SMBV) and inactivated tissue culture vaccine (INACT-TC) used before and during the epizootic were poor immunogens. Prospective studies showed that only about one-third of dogs vaccinated with INACT-SMBV were seropositive 5 weeks after vaccination. Lack of vaccine potency was the most likely cause of poor immunogenicity. Rabies vaccines should be evaluated periodically by measuring antibody responses in animals. In some circumstances, minimum seroconversion rates and antibody titres in vaccinated animals may be better measures of immunogenicity than relative potency.

Evaluation of specificity of indirect enzyme-linked immunosorbent assay for diagnosis of human Q fever

Ninety-five acute- and convalescent-phase serum specimens from 48 patients suspected of having rickettsial or Legionella infections were assayed for antibodies to Coxiella burnetii, the causative agent of Q fever. To evaluate the specificity of the indirect enzyme-linked immunosorbent assay (ELISA) for human Q fever, we compared the ELISA results with those of the indirect immunofluorescence antibody (IFA) test. The ELISA data were analyzed by two different criteria for a positive test. The first criterion for positive results by ELISA was based upon diagnostic titers established in a study of 150 subjects who had no demonstrable cellular or humoral immune responses to C. burnetii phase I or phase II whole cells or phase I lipopolysaccharide. The second criterion was based upon diagnostic antibody titers in a study of 51 subjects who had been diagnosed as having clinical Q fever and had fourfold or greater rises in humoral immune responses to C. burnetii phase I and phase II whole-cell antigens. A comparison of the ELISA and IFA test results of the 95 serum specimens indicated excellent agreement between the tests (Kappa = 92.9%; P < 0.05). None of the 38 patients whose etiologies were confirmed serologically as Legionnaires' disease or rickettsial diseases other than Q fever were classified as positive for C. burnetii by the ELISA. Only one patient identified by the IFA test as having Q fever was not scored positive by the ELISA. These results suggest that the ELISA is useful for epidemiologic screening and as a diagnostic test for human Q fever.

Human ehrlichiosis in the United States, 1985 to 1990

OBJECTIVE

To describe the epidemiology, clinical features, laboratory manifestations, response to therapy, and factors related to morbidity and mortality in a large group of patients with ehrlichiosis.

DESIGN

Case-series.

SETTING

Laboratory-based surveillance in the United States.

PATIENTS

237 patients whose serum had a fourfold increase or decrease in antibodies to Ehrlichia canis or E. chaffeensis.

MEASUREMENTS

Epidemiologic, clinical, laboratory data, hospitalization, duration of illness, complications, and treatment response.

RESULTS

From 1985 through 1990, 237 case-patients were identified in 21 states; rates exceeded 1 per 100,000 per year in only 5 counties. Incidence rates increased with age and were higher among men. Most case-patients had nonspecific illness and were not suspected of having a rickettsial infection. Many patients (60.8%) were hospitalized. Leukocyte and platelet counts typically decreased and liver function tests typically increased through day 7. Three (6.1%) of 49 outpatients treated only with tetracycline were hospitalized compared with 35 (92%) of 38 outpatients treated only with antibiotics other than tetracycline or chloramphenicol (P < 0.001). Among hospitalized patients, recovery was faster for those initially treated with tetracycline (median, 16 days) or chloramphenicol (median, 12 days) than for those initially treated with other antibiotics (median, 27 days; P = 0.03 for both comparisons). In a logistic regression analysis, severe illness or death was more probable among case-patients 60 years or older (odds ratio [OR], 4.60; 95% CI, 1.87 to 11.2) and among those who did not receive tetracycline or chloramphenicol until 8 or more days after symptom onset (OR, 4.38; CI, 1.36 to 14.0).

CONCLUSIONS

The findings of this study are primarily representative of more seriously ill patients with human ehrlichiosis. Although rates are low, ehrlichiosis is found in many areas of the United States. Patients with a history of tick exposure, acute febrile illness, decreasing leukocyte counts, and decreasing platelet counts may have ehrlichiosis. Prompt treatment with tetracycline or chloramphenicol markedly decreases the morbidity.

Risk factors for systemic hypersensitivity reactions after booster vaccinations with human diploid cell rabies vaccine: a nationwide prospective study

To determine the incidence of and risk factors for adverse reactions following the boosters, we conducted a nationwide prospective study of persons receiving pre-exposure booster vaccination with human diploid cell rabies vaccine (HDCV). Persons who had previously received three pre-exposure doses of HDCV and whose rabies neutralizing antibody titres were < or = 1:5 were enrolled in the study if they stated that they intended to receive a booster. Of the 98 persons enrolled in the study, 40 (41%) were in risk groups for whom boosters are not recommended. Three (3%) of 98 developed generalized urticaria or wheezing within 1 day of receiving boosters and three others (3%) developed urticaria 6 to 14 days after the booster. No differences were found between individuals with reactions (either type) and those with no adverse reaction according to age, gender, occupation, history of previous allergies, or time since or route of primary vaccination. Reactions were somewhat more common among persons who received primary vaccinations by the intramuscular route (i.m.) and booster vaccinations by the intradermal route (i.d.) (3/15, 20%) or primary vaccinations i.d. and booster vaccinations i.m. (2/10, 20%), and somewhat less common among persons who received both these vaccinations i.d. (1/52, 2%) or i.m. (0/7). The number of persons who develop allergic reactions may be minimized by administering vaccinations only when vaccination is strictly indicated. The influence of the route of primary and booster vaccinations on the development of reactions deserves further study.

Urban epizootic of rabies in Mexico: epidemiology and impact of animal bite injuries

From 1 July 1987 to 31 December 1988, a total of 317 animals (91% of which were dogs) were confirmed to have rabies in Hermosillo, Mexico. The median age of rabid dogs was 1 year, 69% were male, and 98% were owned. The epizootic started in the southern areas of the city, rapidly involved the entire city, and persisted mainly in lower socioeconomic status areas. The area of the city and mean household size were significant predictor variables for the population density of rabid dogs around household clusters (Poisson linear regression, P < 0.001 and P = 0.03, resp). Approximately 2.5% of city residents were bitten by dogs in 1987, with the rate of reported dog bite injuries being positively correlated with mean household size and the proportion of households that owned dogs. Visits to the city health centre for evaluation of possible exposures to rabies increased by 135% after the start of the epizootic; approximately 273 per 100,000 city residents were administered a full or partial course of rabies post-exposure prophylaxis in 1987. Children were at greatest risk for exposures to rabies, accounting for 60% of all reported animal bite injuries evaluated at the health centre. Also they were more likely than older persons to have received bite injuries to the head, face, and neck (odds ratio = 21.6, 95% confidence interval = 5.4, 186.5).

Benefits and costs of using an orally absorbed vaccine to control rabies in raccoons

In November 1989, the epizootic of rabies affecting raccoons in the mid-Atlantic states reached New Jersey. An economic evaluation was conducted in 2 counties first affected by the epizootic to estimate the costs of the epizootic and to assess the costs and benefits of orally administering a newly developed recombinant rabies vaccine to prevent further spread of the disease. Data on expenditures associated with prevention of rabies in human beings and domestic animals and laboratory testing of suspect animals were collected and analyzed for 1988 (before the epizootic) and 1990 (first full year of the epizootic). Benefit-cost ratios were calculated and used to evaluate the economic advisability of the vaccine at various vaccination program alternatives. Two indices of capital investment analysis, payback period and net present value, were used to evaluate the economic benefits of the rabies vaccine. Expenditures were estimated to be $1,952,014 in 1990 (primarily for pet animal vaccinations), compared with $768,488 in 1988. Benefit-cost ratios ranged from 2.21 for the most expensive vaccination program alternative to 6.80 for the least expensive alternative. The payback period varied from 0.69 to 2.11 years, and the net present value ranged from $2,105,453 to $4,877,452. The high costs of this epizootic necessitated the reallocation of scarce public health resources to various rabies prevention activities, particularly the vaccination of dogs. This study also demonstrated the usefulness of benefit-cost analysis in developing public health strategies. Although the mass application of this recombinant vaccine was found to be economically beneficial, other qualitative considerations must be used to supplement these findings.

Prevention of canine rabies in rural Mexico: an epidemiologic study of vaccination campaigns

We compared three vaccination strategies in three rural communities in Mexico to determine the factors associated with the success of vaccination programs in areas where canine rabies is poorly controlled. In town A, intensive publicity and community participation were used; owners were instructed to bring their dogs to temporary centralized clinics for vaccination. In town B, only brief precampaign publicity was used, followed by vaccination at a centralized site. Minimal publicity was also used in town C, but the vaccination campaign was conducted house to house. A total of 5,426 residents and 1,597 dogs were counted in the three towns (mean human:dog ratio 3.4:1). In Town A, 70.1% (472 of 673) of the dogs were vaccinated; the campaign required 40 person-minutes per dog. Significantly greater proportions were vaccinated in town B (262 of 318 [82.4%]; P less than 0.001) and town C (483 of 561 [86.1%]; P less than 0.00001); each of these latter campaigns required 10 person-minutes per dog. The following factors were positively associated (by multivariate analyses) with vaccination of individual dogs: non-intensive publicity, house-to-house vaccination, dogs owned by a single member of the household, and dogs acquired greater than 15 days after birth. Intensive publicity did not increase the overall success of the vaccination program; the efficiency of centralized versus and house-to-house vaccination was comparable.

A field evaluation in Mexico of four baits for oral rabies vaccination of dogs

We evaluated four baits for the delivery of oral rabies vaccines to dogs. In a controlled study in a town in rural Mexico, 177 randomly selected dogs were assigned to receive one of four experimental baits (two of which were developed by the Denver Wildlife Research Center [DWRC]): one of two cylindrical polyurethane sponges with a corn meal coating (one fried in corn oil [DWRC-corn], the other in fish oil [DWRC-fish]), a fish-flavored polymer bait, or a wax bait. Each dog was also offered a commercial dog biscuit. We recorded whether or not the bait was completely consumed, and used the following measures to estimate the amount of oropharyngeal contact with each bait: total chewing time, presence of pieces of bait on the ground following administration, the total area of ground surrounding the location of ingestion that was covered with green dye contained in each bait, and condition of ampules that contained the dye. The dog biscuits were completely consumed significantly more often than the baits (155 of 176 [88%] for the biscuits versus 89 of 176 [50.5%] for the four baits; P less than 10(-6)), but were chewed for a significantly shorter time than the baits (mean time 34 sec for the biscuit versus 60-82 sec for the four baits: P less than 0.001). The ideal bait would probably combine the attractiveness of the commercial biscuit and the ability of the sponge baits to promote contact with the mucous membranes.

A cluster of Coxiella burnetii infections associated with exposure to vaccinated goats and their unpasteurized dairy products

An outbreak of Q fever occurred among patients and staff of a psychiatric institution in southern France. Some of the patients and staff left the institution daily to work on a farm where goats were raised for raw milk and cheese production. The goats had all been vaccinated annually with a commercial vaccine containing phase II Coxiella burnetii antigen. A serologic survey revealed that 40 (66%) of the 61 patients and staff had elevated titers to C. burnetii. Seropositive persons were more likely to report an acute illness (P = 0.001), fever (P = 0.04), weakness (P = 0.04), arthralgia (P = 0.04), and headaches (P = 0.06) in the preceding year than were seronegative persons. Seropositivity rates were significantly higher among persons who worked on the farm and consumed unpasteurized milk products (69% [22 of 32]; P = 0.007), those who only had worked on the farm (75% [9 of 12]; P = 0.009), and those who only had consumed unpasteurized milk products (75% [9 of 12]; P = 0.009), compared with those who had not worked with the goats or consumed unpasteurized milk products (0 of 5). Despite vaccination against Q fever, no antibodies to C. burnetii were detectable in 17 (59%) of 29 goats. All 12 seropositive goats had antibodies to both phase I and phase II antigens, indicating that they were naturally infected, and two of three goats examined were shedding C. burnetii in their milk. Vaccination of this herd did not prevent the outbreak and might have increased shedding of C. burnetii in the dairy products.

A cluster of tick-borne infections: association with military training and asymptomatic infections due to Rickettsia rickettsii

During the spring of 1989, 86 members of a military unit from the state of Maryland, USA, participated in two-week-long training manoeuvres in the states of Arkansas (location FC) and Virginia (location FAPH). Acute febrile illnesses due to infections with two tick-borne pathogens, Rickettsia rickettsii and Ehrlichia sp., were confirmed serologically in 2 initial cases who were admitted to the hospital. A seroepidemiological investigation among unit members found an additional 17 of 109 individuals (16%) with elevated post-exposure indirect immunofluorescent antibody (IFA) titres to R. rickettsii (16 cases) and/or E. canis (2 cases). The seropositivity rate of personnel who trained at FC was 38% (15 of 40), compared to only 13% (4 of 31) and 8% (3 of 38) of personnel who trained at FAPH or who did not train in the field, respectively (P < 0.001). Seropositivity was associated with symptoms suggestive of a tick-borne illness. Only 4 (22%) and 6 (33%) of the 18 personnel seropositive for R. rickettsii reported an erythematous or petechial type of rash or a febrile illness, respectively, within 4 weeks of exposure; 5 of 18 (28%) personnel infected with R. rickettsii reported no symptoms and only 8 of 18 (44%) received medical treatment. Mild infections with R. rickettsii, or a closely related spotted fever group agent, may have accounted for the high infection rate experienced by this group.

Detection of the etiologic agent of human ehrlichiosis by polymerase chain reaction

Polymerase chain reaction (PCR) primers derived from a variable region of the 16S rRNA gene sequence were used to amplify DNA specifically from Ehrlichia chaffeensis (the recently proposed name for the etiologic agent of human ehrlichiosis). The 389-bp product defined by the specific primers was not detected when DNA samples from any of the other recognized species of Ehrlichia were used as amplification templates. When the PCR was applied to five suitable blood specimens obtained from patients subsequently shown to be serologically positive for E. chaffeensis, all five were positive. The same technique was applied to a total of six control blood specimens, three from febrile patients who had no serologic evidence of infection with Ehrlichia or Rickettsia species and three from patients diagnosed with Rocky Mountain spotted fever, and all six were negative. A chemiluminescent, group-specific oligonucleotide probe was shown to hybridize only with the PCR products obtained upon amplification of the five blood specimens from patients serologically diagnosed as having human ehrlichiosis. The results indicate that PCR, coupled with a nonisotopic method of confirming the identity of the PCR product, is a highly specific and efficient method of detecting the agent of human ehrlichiosis in blood. The results also suggest that E. chaffeensis is the sole etiologic agent of human ehrlichiosis in the United States. The technique was also applied to four ticks that were positive by direct immunofluorescence for Ehrlichia species, and one tick was PCR positive, indicating that E. chaffeensis DNA can be detected in ticks harboring this organism, although the sensitivity may be low.

Rabies surveillance in the United States during 1990

In 1990, the United States and its territories reported 4,881 cases of rabies in animals to the Centers for Disease Control, a 1.5% increase from 1989. Of these, 553 were domestic animals, 4,327 were wild animals, and one was a human being. Pennsylvania reported the highest number (611) of rabies cases in animals in 1990. For the first time since surveillance of rabies in wild animals was begun in the 1950s, the number of cases of rabies in raccoons exceeded that in skunks. Particularly large increases of cases of rabies in wild and domestic animals were reported in New Jersey (469 cases in 1990 compared with 50 cases in 1989, an increase of 838% from 1989) and New York (242 cases in 1990 compared with 54 cases in 1989, an increase of 348%). The 1,821 cases of rabies in raccoons represented a 17.9% increase over those reported in 1989 and 24.5% over those in 1988. This increase was largely attributable to the larger number of rabid raccoons in New Jersey and New York. Other states that reported an increased number of rabies cases in animals in 1990 included Utah (77.8%), Louisiana (64.7%), North Dakota (60.3%), Arizona (28.6%), Oklahoma (27.5%), Delaware (22.2%), and Maryland (20.6%). Thirty states reported a decrease in the number of cases of rabies in animals.

Outbreak of human rabies in the Peruvian jungle

Transmission of rabies to man by vampire bats has been known for 60 years but there have been few reports of the features of rabies transmitted in this way. These aspects of the disease were investigated during an outbreak in Peru in early 1990. Between Jan 1 and April 30, 1990, 29 (5%) of 636 residents of the two rural communities in the Amazon Jungle in Peru acquired an illness characterised by hydrophobia, fever, and headache and died shortly thereafter. A census in one of the two towns revealed that the proportion affected was significantly higher for 5-14 year olds (17%) than for other age-groups (p less than 10(-5). Interviews conducted with 23 of the patients or their families revealed that 22 (96%) had a history of bat bite, compared with 66 (22%) of 301 community members who remained healthy (p less than 10(-6). A rabies virus strain identical to those isolated from vampire bats (Desmodus rotundus) was isolated from the brain of the only person on whom necropsy could be done. Because of the extreme isolation of this and other communities affected by bat-transmitted rabies, preventive measures should be directed at decreasing the risk of nocturnal exposure to bats by bat proofing dwellings or use of mosquito nets and at prompt wound care. Rabies pre-exposure or postexposure vaccination is clearly indicated, but may not be feasible in these isolated populations.

A case of human ehrlichiosis acquired in Mali: clinical and laboratory findings

We report on the clinical, epidemiologic, and laboratory characteristics of the first case of human ehrlichiosis acquired outside the United States caused by an Ehrlichia sp. other than E. sennetsu. The patient, a 24-year-old woman, presumably acquired the infection in Mali in northern Africa; the diagnosis was made when she returned to North America. The patient reported a fever and diarrhea a week before she left Mali; the diarrhea resolved, but the fever and chills continued. She also reported intermittent tingling in both hands and feet and muscle discomfort. Her temperature was 37.8 degrees C and her pulse rate was 100 per minute. She had two erythematous maculopapules (0.5 x 0.7 mm) on her thigh and ankle that resembled infected insect bites. Her hemoglobin level was 148 g/l with normal indices, and her white blood cell count was 10, 500/mm3 with many atypical lymphocytes and platelets. This report is intended to increase physicians' awareness of ehrlichiosis in foreign travelers and other patients, and suggests the need for further research to determine the prevalence and distribution of this disease.

Isolation and characterization of an Ehrlichia sp. from a patient diagnosed with human ehrlichiosis

A new disease was recognized in the United States in 1986. The etiologic agent, although not previously isolated from a human, appeared to be serologically related to Ehrlichia canis, a canine leukotropic rickettsia. We obtained blood specimens from 27 febrile patients with a history of tick exposure. Leukocytes from 24 patients not treated with tetracycline were placed onto a monolayer of DH82 cells. We performed indirect immunofluorescence on sera from all 27 febrile patients as well as sera from 12 patients with previously diagnosed ehrlichiosis. Intractoplasmic inclusions were first observed in culture 35 days after the addition of infected blood from one patient. Partial sequencing of the rRNAs from the human isolate and E. canis indicated that they are 98.7% related. Positive indirect immunofluorescence reactions to the human isolate were obtained for all 12 previously diagnosed patients and for 33% of the 27 febrile patients. Two patients were seropositive for the human isolate but not for E. canis. No sera were positive for E. canis and negative for the human isolate. We report the isolation of a previously unrecognized Ehrlichia sp. that appears to be the etiologic agent of human ehrlichiosis. Serologic data (range of antibody titers, 256 to 32,768) in combination with rRNA sequencing indicated that the newly isolated Ehrlichia sp. is similar, but not identical, to E. canis.

Pre-exposure rabies prophylaxis for travellers: are the benefits worth the cost?

Pre-exposure rabies prophylaxis is recommended by the Immunization Practices Advisory Committee of the US Public Health Services (PHS) as a safe and effective method for reducing the risk of rabies in international travellers. The United States Peace Corps provides pre-exposure prophylaxis with human diploid cell rabies vaccine (HDCV) to over 2000 new volunteers each year going to rabies-endemic countries. During the year November 1987 through October 1988, 175 rabies exposures (and no deaths) were documented in Peace Corps Volunteers serving in 31 rabies-endemic countries, for an overall postexposure treatment rate of 43.6/1000 volunteers per year. Although PHS treatment protocols were strictly followed, the postexposure prophylaxis rate for these Peace Corps Volunteers was 550 times higher than that for the US general population, and 55 times higher than the average rate for 30 developing countries. The use of pre-exposure prophylaxis in travellers was not cost-effective and will not become so until the price of a dose of vaccine declines substantially to $7.00 for the Peace Corps, and even lower for groups with less rabies exposure. However, despite the high vaccine cost, pre-exposure prophylaxis continues to be recommended in the Peace Corps for important non-economic reasons which may also be applicable to other groups of travellers.

One-year study of the 2-1-1 intramuscular postexposure rabies vaccine regimen in 100 severely exposed Thai patients using rabies immune globulin and Vero cell rabies vaccine

The 2-1-1 rabies postexposure treatment schedule is an abbreviated regimen in which a tissue culture rabies vaccine is administered intramuscularly at two sites on day 0, and at one site on days 7 and 21. Compared to the standard five-dose intramuscular regimen, the 2-1-1 schedule reduces the number of clinic visits from five to three and the amount of vaccine used by 20%. One hundred Thai patients, who were severely exposed to rabies, were treated with rabies immune globulin and the 2-1-1 regimen using purified Vero cell rabies vaccine. They were followed for 1 year. Rabies antibody titres were measured in 10% of this group. All patients survived and adverse reactions were mild. A satisfactory antibody response (a titre greater than 0.5 IU ml-1) occurred in all ten patients studied at day 14, but persisted for 90 days in 80% and for 360 days in only 50%. The authors therefore do not recommend use of the 2-1-1 schedule in severely exposed patients who also need to receive rabies immune globulin.

Rabies control in the Republic of the Philippines: benefits and costs of elimination

We compared the benefits and costs of eliminating animal and human rabies in the Philippines. If rabies had been eliminated in 1988, economic benefits would total P52.8 (US$2.5) million in 1989. These benefits would largely arise from the abolition of expenses associated with rabies prevention: P29.7 (US$1.4) million for animal vaccination, P21.6 (US$1.0) million for human postexposure prophylaxis, and P0.3 (US$0.02) million for animal rabies examinations. Benefits also included P1.2 (US$0.06) million in additional earnings of humans whose death due to rabies would be prevented. Nationwide elimination was estimated to cost between P88.1 (US$4.2) million and P317.2 (US$15.0) million, assuming a canine-to-human ratio of 1:10, vaccine coverage of 60%, and a cost per vaccination of no less than P25 (US$1.19) and no more than P90 (US$4.27). These costs would be recouped 4.1-11.0 years after the initiation of a one-year elimination campaign. A sensitivity analysis showed that an elimination programme would be economically beneficial in all but the most extreme cases.

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.