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During 2002 through 2004, 15 patients with Rocky Mountain spotted fever (RMSF) were identified in a rural community in Arizona where the disease had not been previously reported. The outbreak was associated with Rickettsia rickettsii in an unexpected tick vector, the brown dog tick (Rhipicephalus sanguineus), which had not been previously associated with RMSF transmission in the United States. We investigated the extent of exposure to R. rickettsii in the local area through serologic evaluations of children and dogs in 2003–2004, and in canine sera from 1996. Antibodies to R. rickettsii at titers ≥ 32 were detected in 10% of children and 70% of dogs in the outbreak community and 16% of children and 57% of dogs in a neighboring community. In comparison, only 5% of canine samples from 1996 had anti–R. rickettsii antibodies at titers ≥ 32. These results suggest that exposures to RMSF have increased over the past 9 years, and that RMSF may now be endemic in this region.

Rocky Mountain spotted fever (RMSF) is the most commonly reported fatal tick-borne disease in the United States. During 1997–2002, 3,649 cases of RMSF were reported to the Centers for Disease Control and Prevention via the National Electronic Telecommunications System for Surveillance; 2,589 case report forms, providing supplemental information, were also submitted. The average annual RMSF incidence during 1997–2002 was 2.2 cases/million persons. The annual incidence increased during 1997–2002 to a rate of 3.8 cases/million persons in 2002. The incidence was lowest among persons aged <5 and 10–29 years, and highest among adults aged 60–69 years. The overall case-fatality rate was 1.4%; the rate peaked in 1998 at 2.9% and declined to 0.7% in 2001 and 2002. Children <5 years of age had a case-fatality rate (5%) that was significantly greater than the rates for age groups <60 years of age, except for that for 40–49 years of age. Continued national surveillance is needed to assess the effectiveness of prevention efforts and early treatment in decreasing severe morbidity and mortality associated with RMSF.

Cat-scratch disease (CSD), caused by infection with Bartonellahenselae,affects both children and adults but is principally a pediatric disease. Typical CSD is generally benign and self-limited and is characterized by regional lymphadenopathy with fever. Infections can, however, be accompanied by focal or diffuse inflammatory responses (atypical CSD) involving neurologic, organ (liver/spleen), lymphatic or skeletal systems.

Coxiella burnetii, the etiologic agent of Q fever, is a worldwide zoonotic pathogen. Although Q fever is present in the United States, little is known about its current incidence or geographic distribution in either humans or animals. Published reports of national disease surveillance, individual cases, outbreak investigations, and serologic surveys were reviewed to better characterize Q fever epidemiology in the United States. In national disease surveillance reports for 1948-1986, 1,396 human cases were reported from almost every state. Among published individual case reports and outbreak investigations, occupational exposures (research facilities, farm environments, slaughterhouses) were commonly reported, and sheep were most frequently implicated as a possible source of infection. In studies conducted on specific groups, livestock handlers had a significantly higher prevalence of antibodies to C. burnetii than did persons with no known risk. Animal studies showed wide variation in seroprevalence, with goats having a significantly higher average seroprevalence (41.6%) than sheep (16.5%) or cattle (3.4%). Evidence of antibody to C. burnetii was reported among various wild-animal species, including coyotes, foxes, rodents, skunks, raccoons, rabbits, deer, and birds. This literature review suggests that C. burnetii is enzootic among ruminants and wild animals throughout much of the United States and that there is widespread human exposure to this pathogen. Sheep and goats appear to be a more important risk for human infection in the United States than cattle or wild animals, and research studies examining the natural history and transmission risk of Q fever in sheep and goats in this country should be encouraged.

Repetitive tetranucleotide sequences of 5′-(CAAT)n-3′ have been identified at the 5′ end of an open reading frame (ORF) named lob1from Haemophilus somnusstrain 738. Based on sequence analysis, lob1has 59% DNA homology to lex2B, which is involved in lipooligosaccharide (LOS) biosynthesis in H. influenzae.We now report that the number of 5′-CAAT-3′ repeats in lob1varied from 31–35, but that 94% of colonies contained 33 repeats of 5′-CAAT-3′ downstream of two potential start codons, as determined by DNA sequence analysis of the 5′-CAAT-3′ region from individual colonies. If transcription began with the start codon closest to the 5′-CAAT-3′ repeats, a protein of 34.5 kDa would be encoded when 33 repeats were present. However, we could not establish a correlation between the number of 5′-CAAT-3′ repeats in lob1with a specific LOS electrophoretic profile or reactivity with two LOS monoclonal antibodies, indicating multiple genes control LOS phase variation in H. somnus.Complementation of strain 129Pt with lob1containing 33 5 ′-CAAT-3′ repeats in shuttle vector pLS88 resulted in transformants 129Pt(pLSlob1-33A) and 129Pt(pLSlob1-33B), both of which demonstrated the same altered LOS electrophoretic profile. Unlike strain 129Pt, both transformants underwent limited LOS phase variation, which correlated with variation in the number of 5′-CAAT-3′ repeats in pLSlob1-33. Nanoelectrospray-mass spectrometry of O-deacylated LOS indicated that transformant 129Pt(pLSlob1-33A) LOS was composed of a different distribution of glycoforms than LOS of the parent strain. The ratio of glucose to galactose changed from 1:2 in strain 129Pt LOS to 2:1 in transformant 129Pt(pLSlob1-33A) LOS, as determined by gas chromatography-mass spectrometry. Nuclear magnetic resonance spectroscopy confirmed and extended these observations. Transformant 129Pt(pLSlob1-33A) was constitutively more reactive in colony immunoblotting to polyclonal antiserum made to purified strain 738 LOS, and was more susceptible to complement-mediated killing in the presence of anti-738 LOS serum than parent strain 129Pt. Based on these results, Lob1 appears to be a phase variable galactosyl transferase involved in LOS biosynthesis in H. somnus.

ABSTRACTHaemophilus somnusundergoes antigenic and structural phase variation in its lipooligosaccharide (LOS). A gene (lob-1) containing repetitive 5′-CAAT-3′ sequences that may, in part, contribute to phase variation was cloned and sequenced (T. J. Inzana et al., Infect. Immun. 65:4675–4681, 1997). We have now identified another putative gene (lob-2A) immediately upstream from lob-1. Lob-2A contained homology to several LOS biosynthesis proteins of the family Pasteurellaceaeand the LgtB and LgtE galactosyltransferases of Neisseria meningitidisand N. gonorrhoeae. Unlikelob-1, lob-2Acontained 18 to 20 5′-GA-3′ repeats 141 bp upstream of the termination codon as determined by PCR amplification of DNA from individual colonies. Twenty repeats were most common, but when 19 5′-GA-3′ repeats were present a stop codon would occur 1 bp after the last 5′-GA-3′ repeat. A 630-bpSalI-BsgI fragment within lob-2Awas deleted, and a kanamycin resistance (Kmr) gene was inserted into this site to create pCAATΔlob2A. Following electroporation of pCAATΔlob2A into H. somnus738, several allelic exchange mutants were isolated. The LOS electrophoretic profile of one mutant, strain 738-lob2A1::Km, was altered, and the phase variation rate was reduced but phase variation was not eliminated. A variant with 19 5′-GA-3′ repeats in lob-2Ahad an LOS profile similar to that of 738-lob2A1::Km, suggesting that lob-2Awas turned off in this phase. Nanoelectrospray mass spectrometry (nES-MS) and nuclear magnetic resonance spectroscopy showed that 738-lob2A1::Km was deficient in the terminal βGal(1-3)βGlcNAc residue present in parent strain 738. Mutant 738-lob2A1::Km was significantly more sensitive to the bactericidal action of normal bovine serum and was less virulent in mice than was parent strain 738. When H. somnus129Pt was electrotransformed with shuttle vector pLS88 containing lob-2A, its LOS electrophoretic profile was modified and additional N-acetylhexosamine residues were present, as determined by nES-MS analysis. These results indicated thatlob-2Amay be an N-acetylglucosamine transferase involved in LOS biosynthesis and phase variation and that LOS structure is important to H. somnusvirulence.

Prevalence of antibodies to Coxiella burnetii in 24 veterinary school–associated dairy herds in the United States was assessed through laboratory testing of bulk tank milk specimens by indirect immunoflourescent antibody assay. Twenty-two herds (92%) had evidence of antibodies to C. burnetii Phase I antibodies at a titer of ≥1:16, and nine herds (38%) had Phase I antibody titers of ≥1:256. These results suggest that C. burnetii infection is geographically widespread among dairy herds in the United States. Vector-Borne Zoonotic Dis. 5, 90–91.