Effect of the purification process and the storage conditions on the efficacy of an inactivated vaccine against heartwater

This work evaluates the effect of purification process and storage conditions (buffer formulation and temperature) on the efficacy of Ehrlichia ruminantium (ER) elementary bodies to be used as an inactivated vaccine candidate against heartwater. In vitro assays revealed that, to avoid major losses in ER integrity and corresponding antigenic properties, a buffer with pH between 5.6 and 8 and an osmolality above 100 mOsmol/kg H(2)O is recommended. Amongst the tested formulations, both PBS and NaCl have shown to stabilize ER antigens at -20 degrees C. To assess the protective properties of the different vaccine formulations, in vivo experiments were performed using a goat model. The results obtained showed that the preparation of ER antigens using a novel membrane-based purification strategy and a simple vaccine formulation (NaCl, -20 degrees C) induced equivalent protection to the conventional vaccine based on ER antigens prepared by a multistep centrifugation methodology and stored at -20 degrees C in PBS buffer.

Fatal recall responses mediated by CD8 T cells during intracellular bacterial challenge infection

The roles(s) of CD8 T cells during infections by intracellular bacteria that reside in host cell endocytic compartments are not well understood. Our previous studies in a mouse model of human monocytotropic ehrlichiosis indicated that CD8 T cells are not essential for immunity. However, we have observed an unexpected role for these cells during challenge infection. Although immunocompetent mice cleared a primary low-dose (nonfatal) Ixodes ovatus ehrlichia infection, a secondary low-dose challenge infection resulted in fatal disease and loss of control of infection. The outcome was CD8-dependent, because CD8-deficient mice survived secondary low-dose challenge infection. Moreover, effector and/or memory phenotype CD8 T cells were responsible, because adoptive transfer of purified CD44(high) CD8 T cells to naive mice induced fatal responses following a primary low-dose infection. The fatal responses were perforin- and Fas ligand-independent, and were associated with high serum concentrations of TNF-alpha and CCL2, and low levels of IL-10. Accordingly, blockade of either TNF-alpha or CCL2 ameliorated fatal recall responses, and in vitro coculture of memory CD8 T cells and Ixodes ovatus ehrlichia-infected peritoneal exudate cells resulted in substantial increases in TNF-alpha and CCL2. Thus, during monocytotropic ehrlichiosis, inflammatory cytokine production, by CD8 T cells and/or other host cells, can trigger chemokine-dependent disease. These findings highlight a novel role for CD8 T cells, and reveal that live vaccines for intracellular bacteria can, under some conditions, induce undesirable consequences.

An intradermal environment promotes a protective type-1 response against lethal systemic monocytotropic ehrlichial infection

Immune responses against monocytotropic ehrlichiosis during infection with a strain of Ehrlichia from Ixodes ovatus (IOE) were evaluated using a model that closely reproduces the pathology and immunity associated with tick-transmitted human monocytotropic ehrlichiosis. C57BL/6 mice were inoculated intradermally or intraperitoneally with high-dose highly virulent IOE or intraperitoneally with mildly virulent Ehrlichia muris. Intradermal (i.d.) infection with IOE established mild, self-limited disease associated with minimal hepatic apoptosis, and all mice survived past 30 days. Intraperitoneal (i.p.) infection with IOE resulted in acute, severe toxic shock-like syndrome and severe multifocal hepatic apoptosis and necrosis, and all mice succumbed to disease. Compared to i.p. infection with IOE, intradermally infected mice had a 100- to 1,000-fold lower bacterial load in the spleen with limited dissemination. Compared to mice infected intraperitoneally with IOE, i.d. infection stimulated a stronger protective type-1 cell-mediated response on day 7 of infection, characterized by increased percentages of both CD4+ and CD8+ splenic T cells, generation of a greater number of IOE-specific, gamma interferon-producing CD4+ Th1 cells, and higher levels of tumor necrosis factor (TNF-alpha) in the spleen but lower concentrations of serum TNF-alpha and interleukin-10. These data suggest that under the conditions of natural route of challenge (i.e., i.d. inoculation), the immune response has the capacity to confer complete protection against monocytotropic ehrlichiosis, which is associated with a strong cell-mediated type-1 response and decreased systemic production of pro- and anti-inflammatory cytokines.

Susceptibility and resistance to monocytic ehrlichiosis in the mouse

To address the role of cellular immunity during ehrlichia infection, we have utilized a model of monocytic ehrlichiosis that results from infection of mice by Ixodes ovatus ehrlichia (IOE). Although ehrlichiosis in humans is largely a disease of immunocompromised individuals, the use of the IOE model has allowed us to identify factors required for host defense in normal mice. Using a low-dose infection C57BL/6 mouse model, we have demonstrated that host defense requires immune mechanisms involving CD4 T cell-mediated, TNF-alpha-, IL-12-, and IFN-gamma-dependent, macrophage activation. We have also provided formal evidence that IFN-gamma produced by CD4 Th1 cells is sufficient for protective immunity. Our recent studies have demonstrated, in addition, an essential role for IL-10, which is probably important in inhibiting immunopathological responses, and for inducible nitric oxide synthase. The latter observation establishes an important role for reactive nitrogen intermediates in bacterial elimination in vivo. In contrast, evaluation of mice carrying wild-type and mutant alleles of Nramp1 revealed at most a modest role for this gene in resistance to fatal IOE infection. Other studies in low-dose infected mice have indicated that the generation of immunological memory may be impaired during low-dose IOE infection, possibly due to bacterial immune subversion. These studies highlight the utility of the IOE mouse model in identifying important parameters of the immune response during ehrlichiosis.

Role of tumor necrosis factor alpha (TNF-alpha) and interleukin-10 in the pathogenesis of severe murine monocytotropic ehrlichiosis: increased resistance of TNF receptor p55- and p75-deficient mice to fatal ehrlichial infection

Intraperitoneal (i.p.) infection with a high dose of a highly virulent Ehrlichia strain (IOE) results in a toxic shock-like syndrome characterized by severe liver injury and systemic overproduction of tumor necrosis factor alpha (TNF-alpha) by CD8+ T cells. We examined the role of TNF-alpha and TNF receptors in high-dose-IOE-induced shock/liver injury. TNF receptor (TNFR) I/II-/- mice lacking both the p55 and p75 receptors for this cytokine were more resistant to IOE-induced liver injury than their wild-type background controls. TNFR I/II-/- mice survived longer, dying between 15 and 18 days, with evidence of mild liver necrosis/apoptosis. In contrast, wild-type mice were not rescued from the lethal effect of IOE by TNF-alpha neutralization. TNF-alpha-depleted mice developed severe liver injury and succumbed to disease between days 9 and 11 postinfection, similar to sham-treated, infected wild-type mice. Although IFN-gamma production in the spleens of IOE-infected TNFR I/II-/- and TNF-alpha-depleted mice was higher than that detected in wild-type controls, these mice had higher bacterial burdens than infected controls. Following high-dose IOE challenge, TNFR I/II-/- and TNF-alpha-depleted mice have an early increase in IL-10 levels in sera and spleens, which was produced mainly by adherent spleen cells. In contrast, a late burst of interleukin-10 (IL-10) was observed in control mice. Nonadherent spleen cells were the major source of IL-10 in IOE-infected wild-type mice. We conclude that TNFR I/II and TNF-alpha participate in Ehrlichia-induced shock and host defense by regulating liver injury and controlling ehrlichial burden. Our data suggest that fatal ehrlichiosis could be a multistep process, where TNF-alpha is not solely responsible for mortality.

The Ticking Time Bomb

A man with orbital myositis and optic neuritis tested positive serologically for multiple tick-borne diseases. Erlichiosis, babesiosis, and Lyme disease may occur together and affect the eye or orbit.

First Evidence of Feline Herpesvirus, Calicivirus, Parvovirus, and Ehrlichia Exposure in Brazilian Free-ranging Felids

Serum samples from 18 pumas (Puma concolor), one ocelot (Leopardus pardalis), and two little spotted cats (Leopardus tigrinus) collected from free-ranging animals in Brazil between 1998 and 2004 were tested by indirect immunofluorescence (IFA) for antibodies to feline herpesvirus 1 (FHV 1), calicivirus (FCV), coronavirus (FCoV), parvo-virus (FPV), Ehrlichia canis, Anaplasma pha-gocytophilum, and Bartonella henselae. Serum samples also were tested, by Western blot and ELISA, for feline leukemia virus (FeLV) specific antibodies and antigen, respectively, by Western blot for antibodies to feline immunodeficiency virus (FIV), and by indirect ELISA for antibodies to puma lentivirus (PLV). Antibodies to FHV 1, FCV, FCoV, FPV, FeLV, FIV, PLV or related viruses, and to B. henselae were detected. Furthermore, high-titered antibodies to E. canis or a closely related agent were detected in a puma for the first time.

Experimental inoculation of beagle dogs with Ehrlichia species detected from Ixodes ovatus

Three beagle dogs were inoculated with mice spleen/liver homogenate infected with Ehrlichia species detected from Ixodes ovatus (EIO) and one dog was used as a control. All three infected dogs did not show clinical signs of disease except for mild pyrexia throughout the 41-day study period. Splenomegaly was observed from Day 7 post-inoculation (p.i.) in two of the dogs. Hematological and biochemical abnormalities included mild thrombocytopenia, hypoproteinaemia, hypoalbuminaemia and increased C-reactive protein values. One of the dogs' splenic aspirate sample was PCR-positive for Ehrlichia Day 7 p.i. and another dogs' blood and bone marrow aspirate sample was PCR-positive Day 41 p.i. Sequence analysis of the PCR products showed 100% homology with the 16SrRNA partial gene sequence of Ehrlichia sp. HF565. Antibody titers to EIO were observed in all three experimentally infected dogs starting from the first week p.i. and cross-reactivity with Ehrlichia canis was detectable in one of the dogs starting Day 7 p.i. These data suggest that infection of dogs with EIO is possible, though is probably of low pathogenic importance. Cross-reactivity of EIO infected dog serum with E. canis raises the likelihood of false E. canis seropositive dogs.

Ehrlichia under our noses and no one notices

Ehrlichia chaffeensis, an obligately intracellular bacterium, resides within a cytoplasmic vacuole in macrophages, establishes persistent infection in natural hosts such as white-tailed deer and canids, and is transmitted transstadially and during feeding by ticks, particularly Amblyomma americanum. Ehrlichial cell walls contain glycoproteins and a family of divergent 28 kDa proteins, but no peptidoglycan or lipopolysaccharide. The dense-cored ultrastructural form preferentially expresses certain glycoproteins, including a multiple repeat unit-containing adhesin. Ehrlichiae attach to L-selectin and E-selectin, inhibit phagolysosomal fusion, apoptosis, and JAK/STAT activation, and downregulate IL-12, IL-15, IL-18, TLR2 and 3, and CD14. Mouse models implicate overproduction of TNF-alpha by antigen-specific CD8 T lymphocytes in pathogenesis and strong type 1 CD4 and CD8 T lymphocyte responses, synergistic activities of IFN-gamma and TNF-alpha, and IgG2a antibodies in immunity. Human monocytotropic ehrlichiosis (HME) manifests as a flu-like illness that progresses in severity to resemble toxic shock-like syndrome, with meningoencephalitis or adult respiratory distress syndrome in some patients, and requires hospitalization in half. In immunocompromised patients, HME acts as an overwhelming opportunistic infection. In one family physician's practice, active surveillance for three years revealed an incidence of 1000 cases per million population. Diagnosis employs serology or polymerase chain reaction, which are not utilized sufficiently to establish the true impact of this emerging virus-like illness.

Ehrlichial infection in Cameroonian canines by Ehrlichia canis and Ehrlichia ewingii

Ehrlichia chaffeensis and Ehrlichia ewingii are agents of emerging human ehrlichioses in North America and are transmitted primarily by Amblyomma americanum ticks, while Ehrlichia canis is the globally distributed cause of canine monocytic ehrlichiosis (CME) and is transmitted by the brown dog tick, Rhipicephalus sanguineus. Although E. canis and Ehrlichia ruminantium are endemic in Africa, the presence of ehrlichial agents in dogs and ticks in Cameroon has not been investigated. The objective of this study was to determine the prevalence of ehrlichial infections in Cameronian dogs using a combination of serologic and molecular methods. Peripheral blood was collected, clinical signs and the presence or absence of ticks on dogs (n=104) presenting for various reasons at local veterinary clinics around the Mount Cameroon region were noted. IFA identified 33 dogs (32%) with antibodies reactive with E. canis, and reactivity of these sera with all major E. canis antigens (200, 140, 95, 75, 47, 36, 28, and 19-kDa) was confirmed by immunoblotting. Multicolor real-time PCR detected ehrlichial DNA (E. canis (15) and E. ewingii (2)) in 17 dogs (16.3%), all of which had attached ticks at time of presentation. The dsb amplicons (378 bp) from E. canis and E. ewingii were identical to gene sequences from North American isolates. This study identifies canine ehrlichiosis as a prevalent unrecognized cause of disease in Cameroonian canines.

Immunity to the ehrlichiae: new tools and recent developments

PURPOSE OF REVIEW

Discusses recent developments in the study of immunity and host defense against the monocytic ehrlichiae in 2003 and 2004. The review does not address anaplasmoses, as the anaplasmae were recently re-classified into the genus Anaplasma, and are distinct in cell tropism from the ehrlichiae.

RECENT FINDINGS

The features of the immune responses against these emerging Gram-negative obligate intracellular pathogens are only beginning to be understood. Important advances in our ability to study host defense include the development of new experimental mouse models. Recent studies have defined possible mechanisms of innate immune subversion in human monocytes, as well as roles for lymphocyte subsets and type I cytokines during mouse infection. Other studies in the mouse suggest that cytokine production by CD8 T cells may contribute to immunopathology. New data also support a role for humoral immunity during host defense against these intracellular pathogens.

SUMMARY

The use of new animal models will facilitate research of the mechanisms of innate, adaptive, and pathological immune responses, and will enhance our understanding of human immunity to the ehrlichiae as well as to other pathogenic intracellular bacteria.

Ehrlichiosis y anaplasmosis humana

Human ehrlichiosis and anaplasmosis are acute febrile tick-borne diseases caused by various species of the genera Ehrlichia and Anaplasma (Anaplasmataceae). To date, only cases of human granulocytic anaplasmosis (HGA) caused by Anaplasma phagocytophilum (formerly human granulocytic Ehrlichia, Ehrlichia phagocytophila, and E. equi) have been diagnosed in Europe. HGA and Lyme borreliosis are closely related diseases that share vector and reservoirs. In addition to HGA, human monocytic ehrlichiosis caused by E. chaffeensis has been reported in North America, as well as cases of infection due to E. ewingii in immunocompromised hosts. Ehrlichia spp. and A. phagocytophilum have tropism for blood cells, especially leukocytes and platelets, causing a considerable decrease of both components in these patients. HGA should be suspected in tick-bitten patients or those who have visited an endemic area and show symptoms of flu-like fever, leukopenia and thrombocytopenia.

Detection ofEhrlichiaspp. in Raccoons (Procyon lotor) from Georgia

Raccoons (Procyonis lotor) and opossums (Didelphis virginianus) acquired from six contiguous counties in the Piedmont physiographic region of Georgia were investigated for their potential role in the epidemiology of ehrlichial and anaplasmal species. Serum was tested by indirect fluorescent antibody (IFA) assay for the presence of antibodies reactive to Ehrlichia chaffeensis, E. canis, and Anaplasma phagocytophilum (HGA agent). Nested polymerase chain reaction (PCR) assay was used to test whole blood or white blood cell preparations for the presence of Ehrlichia and Anaplasma spp. 16S rRNA (rDNA) gene fragments. In addition, ticks were collected from these animals and identified. Twenty-three of 60 raccoons (38.3%) had E. chaffeensis-reactive antibodies (>1:64), 13 of 60 raccoons (21.7%) had E. canis-reactive antibodies, and one of 60 raccoons (1.7%) had A. phagocytophilum- reactive antibodies. A sequence confirmed E. canis product was obtained from one of 60 raccoons and a novel Ehrlichia-like 16S rDNA sequence was detected in 32 of 60 raccoons. This novel sequence was most closely related to an Ehrlichia-like organism identified from Ixodes ticks and rodents in Asia and Europe. Raccoons were PCR negative for E. chaffeensis and E. ewingii DNA. Five tick species, including Dermacentor variabilis, Amblyomma americanum, Ixodes texanus, I. cookei, and I. scapularis, were identified from raccoons and represent potential vectors for the ehrlichiae detected. Opossums (n = 17) were free of ticks and negative on all IFA and PCR assays. This study suggests that raccoons are potentially involved in the epidemiology of multiple ehrlichial organisms with known or potential public health and veterinary implications.

Serological Evidence of Ehrlichia spp. Exposure in Cats from Northeastern Spain

There is little information about Ehrlichia canis as an infectious agent in cats. In order to estimate the prevalence of antibodies to E. canis in the feline population, 235 cat sera were analysed by indirect fluorescent-antibody test. With the objective to determine some risk factors associated with seropositivity, serum samples were divided into two groups: urban stray cats and pet cats. The seroprevalence detected was 17.9%. Most positive sera (83.3%) showed low antibody titres (<1:80). Seropositivity was very similar when comparing the two groups of animals: 17.4% in urban stray cats and 18.4% in pet cats. Results revealed that cats are exposed to Ehrlichia spp. infection, as the low antibody titres detected and the serological cross-reactivity between Ehrlichia species do not allow us to confirm E. canis exposure.

Exogenous and endogenous glycolipid antigens activate NKT cells during microbial infections

CD1d-restricted natural killer T (NKT) cells are innate-like lymphocytes that express a conserved T-cell receptor and contribute to host defence against various microbial pathogens. However, their target lipid antigens have remained elusive. Here we report evidence for microbial, antigen-specific activation of NKT cells against Gram-negative, lipopolysaccharide (LPS)-negative alpha-Proteobacteria such as Ehrlichia muris and Sphingomonas capsulata. We have identified glycosylceramides from the cell wall of Sphingomonas that serve as direct targets for mouse and human NKT cells, controlling both septic shock reaction and bacterial clearance in infected mice. In contrast, Gram-negative, LPS-positive Salmonella typhimurium activates NKT cells through the recognition of an endogenous lysosomal glycosphingolipid, iGb3, presented by LPS-activated dendritic cells. These findings identify two novel antigenic targets of NKT cells in antimicrobial defence, and show that glycosylceramides are an alternative to LPS for innate recognition of the Gram-negative, LPS-negative bacterial cell wall.

Seroepidemiological study of canine ehrlichial infections in Yamaguchi prefecture and surrounding areas of Japan

Randomly selected serum samples from 150 dogs from Yamaguchi and neighbouring prefectures were subjected to the indirect immunofluorescent assay to detect antibodies against Ehrlichia canis, Ehrlichia chaffeensis, Ehrlichia muris and Ehrlichia from Ixodes ovatus. A total of 30 out of the 150 serum samples reacted with at least one of the antigens at a titer of 1:20 or more. Considerable cross-reactivity was seen and most samples reacted with at least two different antigens. Fifteen (10.0%) dogs had higher titers to E. canis than any of the other antigens. Four (2.7%) dogs had higher titers to Ehrlichia from Ixodes ovatus and one (0.6%) dog had higher titers to E. muris compared to the other antigens. The findings suggest that these five dogs may be infected with the domestic Ehrlichia of Japan. The remaining ten dogs had similar high titers to two or more of the antigens. This is the first serological evidence obtained of canine infection with the domestic Ehrlichia of Japan.

Mechanisms of immunity to Ehrlichia muris: a model of monocytotropic ehrlichiosis

Ehrlichia species can cause life-threatening infections or chronic persistent infections. Mechanisms of protective immunity were examined in an Ehrlichia muris mouse model of monocytotropic ehrlichiosis. C57BL/6 mice possessed strong genetic resistance to E. muris of an undetermined mechanism. CD8 T lymphocytes were particularly important, as revealed by 81% fatalities for E. muris-infected, major histocompatibility complex class I gene knockout mice compared with no deaths for wild-type C3H mice. Moreover, 80% of C3H mice depleted of CD8 and CD4 cells died of E. muris infection compared with only 44% of CD4 cell-depleted mice. CD8 T lymphocytes were demonstrated for the first time in an Ehrlichia infection to exhibit cytotoxic T-lymphocyte activity against Ehrlichia-infected target cells. Both gamma interferon and tumor necrosis factor were shown to play synergistic roles in protective immunity in vivo for the first time, as demonstrated by 75% fatalities when both cytokines were neutralized compared with minimal mortality when they were depleted separately. Passive transfer of antibodies, but not Fab fragments, to E. muris protected C3H/SCID mice against lethal infection. The mechanism of increased susceptibility (22% lethality) of C57BL/6 major histocompatibility complex class II gene knockout mice and CD4 cell-depleted C3H mice (i.e., through a gamma interferon or antibody mechanism), as well as the more important role of CD8 T lymphocytes (in the form of cytotoxic T-lymphocyte activity and/or gamma interferon production), remains to be elucidated. Protective immunity against monocytotropic E. muris is mediated by a combination of CD8 and CD4 T lymphocytes, gamma interferon, tumor necrosis factor alpha, and antibodies.

Overproduction of TNF-α by CD8+Type 1 Cells and Down-Regulation of IFN-γ Production by CD4+Th1 Cells Contribute to Toxic Shock-Like Syndrome in an Animal Model of Fatal Monocytotropic Ehrlichiosis

Human monocytotropic ehrlichiosis (HME) is an emerging, life-threatening, infectious disease caused by Ehrlichia chaffeensis, an obligate intracellular bacterium that lacks cell wall LPS. We have previously developed an animal model of severe HME using a strain of Ehrlichia isolated from Ixodes ovatus ticks (IOE). To understand the basis of susceptibility to severe monocytotropic ehrlichiosis, we compared low and high doses of the highly virulent IOE strain and the less virulent Ehrlichia muris strain that are closely related to E. chaffeensis in C57BL/6 mice. Lethal infections caused by high or low doses of IOE were accompanied by extensive liver damage, extremely elevated levels of TNF-alpha in the serum, high frequency of Ehrlichia-specific, TNF-alpha-producing CD8(+) T cells in the spleen, decreased Ehrlicha-specific CD4(+) T cell proliferation, low IL-12 levels in the spleen, and a 40-fold decrease in the number of IFN-gamma-producing CD4(+) Th1 cells. All groups contained negligible numbers of IL-4-producing cells in the spleen. Transfer of Ehrlichia-specific polyclonal Abs and IFN-gamma-producing Ehrlichia-specific CD4(+) and CD8(+) type 1 cells protected naive mice against lethal IOE challenge. Interestingly, infection with high dose E. muris provided protection against rechallenge with a lethal dose of IOE. Cross-protection was associated with substantial expansion of IFN-gamma-producing CD4(+) and CD8(+) cells, but not TNF-alpha-producing CD8(+) T cells, a high titer of IgG2a, and a low serum level of TNF-alpha. In conclusion, uncontrolled TNF-alpha production by CD8(+) T cells together with a weak CD4(+) Th1 cell response are associated with immunopathology and failure to clear IOE in the fatal model of HME.

Predominance of Ehrlichia ewingii in Missouri dogs

To investigate the species distribution of Ehrlichia present in Missouri dogs, we tested 78 dogs suspected of having acute ehrlichiosis and 10 healthy dogs. Blood from each dog was screened with a broad-range 16S rRNA gene PCR assay that detects known pathogenic species of Ehrlichia and ANAPLASMA: The species was determined by using species-specific PCR assays and nucleotide sequencing. Ehrlichia antibody testing was performed by using an indirect immunofluorescence assay with Ehrlichia chaffeensis as the antigenic substrate. The broad-range assay detected Ehrlichia or Anaplasma DNA in 20 (26%) of the symptomatic dogs and 2 (20%) of the asymptomatic dogs. E. ewingii accounted for 20 (91%), and E. chaffeensis accounted for 1 (5%) of the positives. Anaplasma phagocytophilum DNA was detected in one dog, and the sequences of regions of the 16S rRNA gene and the groESL operon amplified from the blood of this dog matched the published sequences of this organism. Antibodies reactive with E. chaffeensis were detected in 14 (67%) of the 21 PCR-positive dogs and in 12 (19%) of the 64 PCR-negative dogs. Combining the results of PCR and serology indicated that 33 (39%) of 85 evaluable dogs had evidence of past or current Ehrlichia infection. We conclude that E. ewingii is the predominant etiologic agent of canine ehrlichiosis in the areas of Missouri included in this survey. E. canis, a widely recognized agent of canine ehrlichiosis, was not detected in any animal. The finding of E. ewingii in asymptomatic dogs suggests that dogs could be a reservoir for this Ehrlichia species.

Kinetics of antibody response to Ehrlichia canis immunoreactive proteins

Immunoreactive proteins of Ehrlichia canis and Ehrlichia chaffeensis that have been characterized include a family of 28-kDa major outer membrane proteins (p28) and two large antigenically divergent surface glycoprotein orthologs. We previously demonstrated that recombinant E. canis p28 and the 140- and 200-kDa glycoproteins gp140 and gp200, respectively, react strongly with serum antibodies from suspect canine ehrlichiosis cases that were positive for E. canis by immunofluorescent antibody test and in various phases of acute or chronic infection (J. Clin. Microbiol. 39:315-322, 2001). The kinetics of the antibody response to these potentially important vaccine and immunodiagnostic candidates is not known. Acute-phase serum antibody responses to whole-cell E. canis lysates and recombinant p28, gp140, and gp200 were monitored for 6 weeks in dogs experimentally infected with E. canis. Irrespective of the inoculation route, a T-helper 1-type response was elicited to E. canis antigens consisting of immunoglobulin G2 antibodies exclusively in both acute and convalescent phases in most dogs. Analysis of immuoreactive antigens for peak intensity and relative quantity identified major immunoreactive E. canis antigens recognized early in the infection as the 19-, 37-, 75-, and 140-kDa proteins. Later in infection, additional major immunoreactive E. canis proteins were identified, including the 28-, 47-, and 95-kDa proteins and the recently identified 200-kDa glycoprotein. All dogs had developed antibody against the recombinant gp140, gp200, and p28 in the convalescent phase. Immunoreactivity and antibody response kinetics suggest that major immunoreactive proteins identified are immunodominant, but early recognition suggests increased dominance by some antigens.

Fort Chaffee revisited: the epidemiology of tick-borne rickettsial and ehrlichial diseases at a natural focus

A retrospective cohort study was conducted among troops training at Fort Chaffee, Arkansas, from May through June 1997, to identify infections caused by tick-borne pathogens. Serum samples were tested by IFAs for antibodies to selected Rickettsia and Ehrlichia species and by an investigational EIA for spotted fever group Rickettsia lipopolysaccharide antigens. Of 1,067 guardsmen tested, 162 (15.2%) had antibodies to one or more pathogens. Of 93 guardsmen with paired serum samples, 33 seroconverted to Rickettsia rickettsii or spotted fever group rickettsiae (SFGR) and five to Ehrlichia species. Most (84.8%) of the personnel who seroconverted to SFGR were detected only by EIA, and seropositivity was significantly associated with an illness compatible with a tick-borne disease. In addition, 34 (27%) of 126 subjects with detectable antibody titers reported a compatible illness. The primary risk factor for confirmed or probable disease was finding > 10 ticks on the body. Doxycycline use and rolling up of long sleeves were protective against seropositivity. The risk of transmission of tick-borne pathogens at Fort Chaffee remains high, and use of the broadly reactive EIA suggests that previous investigations may have underestimated the risk for infection by SFGR. Measures to prevent tick bite and associated disease may require reevaluation.

Ehrlichiosis optic neuritis

PURPOSE

To describe a case of ehrlichiosis optic neuritis.

DESIGN

Single observational case report.

METHODS

A 41-year-old woman with symptoms and clinical and imaging signs consistent with optic neuritis presented to a tertiary care academic center for comprehensive neuro-ophthalmic evaluation. Main outcome measures included preoptic and postoptic neuritis polyvalent ehrlichiosis titers and magnetic resonance imaging (MRI) of orbits with gadolinium.

RESULTS

Ehrlichiosis titers drawn 11 days before onset of eye symptoms were negative. Titers drawn 7 days after symptoms began were positive. The optic nerve enhanced with gadolinium on MRI.

CONCLUSIONS

Ehrlichiosis can cause optic neuritis and should be considered in patients with optic neuritis after a febrile, flu-like illness in an endemic area.

Comparison of serological detection methods for diagnosis of Ehrlichia canis infections in dogs

We determined the value of four serological assays for the diagnosis of canine monocytic ehrlichiosis by comparing them to the indirect fluorescent-antibody assay "gold standard." The specificity of Dip-S-Ticks was significantly lower than that of all of the other tests evaluated. The sensitivity of Dip-S-Ticks was significantly higher than that of Snap3Dx or the Snap Canine Combo. The sensitivity of the rMAP2 enzyme-linked immunosorbent assay (ELISA) was significantly higher than that of the Snap Canine Combo. The accuracy levels of the rMAP2 ELISA, Snap3Dx, Dip-S-Ticks, and Snap Canine Combo were 97.0, 89.8, 85.1, and 82.9%, respectively.