A case of concurrent Lyme meningitis with ehrlichiosis

Ehrlichiosis presenting as severe sepsis and meningoencephalitis in an immunocompetent adult

Introduction

Ehrlichia are obligate intracellular pathogens transmitted to vertebrates by ticks.

Case presentation

We report the case of a 59-year-old man who presented to the University of Kentucky Albert B. Chandler Medical Center (Lexington, KY, USA) after being found fallen down in the woods. A lumbar puncture revealed what appeared to be bacterial meningitis, yet cerebrospinal fluid cultures, Gram stains and a meningitis/encephalitis panel were inconclusive. However, an Ehrlichia DNA PCR of the blood resulted as being positive for Ehrlichia chaffeensis antibodies. The patient received a 14 day course of doxycycline, and recovered from his multiple organ failure. The aetiology of the ehrlichial meningoencephalitis was likely transmission through a tick-bite, due to the patient's outdoor exposure.

Conclusion

While it is rare to see Ehrlichia as a cause of meningitis, this illness can progress to severe multisystem disease with septic shock, meningoencephalitis or acute respiratory distress syndrome (ARDS). Those with compromised immunity are at a higher risk of developing the more severe form of the disease and have higher case fatality rates.

Mechanisms of obligatory intracellular infection with Anaplasma phagocytophilum

Anaplasma phagocytophilum persists in nature by cycling between mammals and ticks. Human infection by the bite of an infected tick leads to a potentially fatal emerging disease called human granulocytic anaplasmosis. A. phagocytophilum is an obligatory intracellular bacterium that replicates inside mammalian granulocytes and the salivary gland and midgut cells of ticks. A. phagocytophilum evolved the remarkable ability to hijack the regulatory system of host cells. A. phagocytophilum alters vesicular traffic to create an intracellular membrane-bound compartment that allows replication in seclusion from lysosomes. The bacterium downregulates or actively inhibits a number of innate immune responses of mammalian host cells, and it upregulates cellular cholesterol uptake to acquire cholesterol for survival. It also upregulates several genes critical for the infection of ticks, and it prolongs tick survival at freezing temperatures. Several host factors that exacerbate infection have been identified, including interleukin-8 (IL-8) and cholesterol. Host factors that overcome infection include IL-12 and gamma interferon (IFN-γ). Two bacterial type IV secretion effectors and several bacterial proteins that associate with inclusion membranes have been identified. An understanding of the molecular mechanisms underlying A. phagocytophilum infection will foster the development of creative ideas to prevent or treat this emerging tick-borne disease.

Molecular characterization of Anaplasma phagocytophilum and Borrelia burgdorferi in Ixodes scapularis ticks from Pennsylvania

Ixodes scapularis ticks were collected in 2000 and 2001 from two areas in Pennsylvania and tested for the presence of Anaplasma phagocytophilum and Borrelia burgdorferi by PCR and DNA sequencing. Of the ticks collected from northwestern and southeastern Pennsylvania, 162 of 263 (61.6%) and 25 of 191 (13.1%), respectively, were found to be positive for B. burgdorferi. DNA sequencing showed >99% identity with B. burgdorferi strains B31 and JD1. PCR testing for A. phagocytophilum revealed that 5 of 263 (1.9%) from northwestern Pennsylvania and 76 of 191 (39.8%) from southeastern Pennsylvania were positive. DNA sequencing revealed two genotypes of A. phagocytophilum, the human granulocytic ehrlichiosis (HGE) agent and a variant (AP-Variant 1) that has not been associated with human infection. Although only the HGE agent was present in northwestern Pennsylvania, both genotypes were found in southeastern Pennsylvania. These data add to a growing body of evidence showing that AP-Variant 1 is the predominant agent in areas where both genotypes coexist.

Ehrlichia chaffeensis: a prototypical emerging pathogen

Ehrlichia chaffeensis is an obligately intracellular, tick-transmitted bacterium that is maintained in nature in a cycle involving at least one and perhaps several vertebrate reservoir hosts. The moderate to severe disease caused by E. chaffeensis in humans, first identified in 1986 and reported for more than 1,000 patients through 2000, represents a prototypical "emerging infection." Knowledge of the biology and natural history of E. chaffeensis, and of the epidemiology, clinical features, and laboratory diagnosis of the zoonotic disease it causes (commonly referred to as human monocytic ehrlichiosis [HME]) has expanded considerably in the period since its discovery. In this review, we summarize briefly the current understanding of the microbiology, pathogenesis, and clinical manifestations associated with this pathogen but focus primarily on discussing various ecological factors responsible for the recent recognition of this important and potentially life-threatening tick-borne disease. Perhaps the most pivotal element in the emergence of HME has been the staggering increases in white-tailed deer populations in the eastern United States during the 20th century. This animal serves as a keystone host for all life stages of the principal tick vector (Amblyomma americanum) and is perhaps the most important vertebrate reservoir host for E. chaffeensis. The contributions of other components, including expansion of susceptible human populations, growth and broadening geographical distributions of other potential reservoir species and A. americanum, and improvements in confirmatory diagnostic methods, are also explored.

Coinfecting deer-associated zoonoses: Lyme disease, babesiosis, and ehrlichiosis

The heightened worldwide recognition of the health burden of tickborne infection derives largely from the increasing incidence of Lyme disease, human babesiosis, and human granulocytic ehrlichiosis, both individually and in concert. Because these infections share the same rodent reservoir and tick vector hosts, they can be cotransmitted to human hosts. Indeed, human coinfections involving various combinations of these pathogens are common, and some tend to be particularly severe. Diagnostic procedures and clinical management of the resulting disease syndrome is rendered complex by the diversity of pathogens involved and by the unusual diversity and duration of symptoms.

Coinfection with Borrelia burgdorferi and the agent of human granulocytic ehrlichiosis alters murine immune responses, pathogen burden, and severity of Lyme arthritis

Lyme disease and human granulocytic ehrlichiosis (HGE) are tick-borne illnesses caused by Borrelia burgdorferi and the agent of HGE, respectively. We investigated the influence of dual infection with B. burgdorferi and the HGE agent on the course of murine Lyme arthritis and granulocytic ehrlichiosis. Coinfection resulted in increased levels of both pathogens and more severe Lyme arthritis compared with those in mice infected with B. burgdorferi alone. The increase in bacterial burden during dual infection was associated with enhanced acquisition of both organisms by larval ticks that were allowed to engorge upon infected mice. Coinfection also resulted in diminished interleukin-12 (IL-12), gamma interferon (IFN-gamma), and tumor necrosis factor alpha levels and elevated IL-6 levels in murine sera. During dual infection, IFN-gamma receptor expression on macrophages was also reduced, implying a decrease in phagocyte activation. These results suggest that coinfection of mice with B. burgdorferi and the HGE agent modulates host immune responses, resulting in increased bacterial burden, Lyme arthritis, and pathogen transmission to the vector.

Tick-borne pulmonary disease: update on diagnosis and management

Ticks are capable of transmitting viruses, bacteria, protozoa, and rickettsiae to man. Several of these tick-borne pathogens can lead to pulmonary disease. Characteristic clinical features, such as erythema migrans in Lyme disease, or spotted rash in a spotted fever group disease, may serve as important diagnostic clues. Successful management of tick-borne diseases depends on a high index of suspicion and recognition of their clinical features. Patients at risk for tick bites may be coinfected with two or more tick-borne pathogens. A Lyme vaccine has recently become available for use in the United States. Disease prevention depends on the avoidance of tick bites. When patients present with respiratory symptoms and a history of a recent tick bite or a characteristic skin rash, a differential diagnosis of a tick-borne pulmonary disease should be considered. Early diagnosis and appropriate antibiotic therapy for these disorders lead to greatly improved outcomes.

Ehrlichiosis

HGE and HME have been recognized as distinct clinical conditions for only 5 and 10 years, respectively, and much information regarding their ecology and epidemiology remains uncertain. The nonspecific character of the illness complicates this incomplete knowledge, as an unknown percentage of infections are likely misdiagnosed. Ehrlichiosis should be considered in any patient presenting with flu-like illness and history of a tick bite. Although expanding, diagnostic support for human ehrlichioses is currently limited to a few regional academic and public health laboratories. Healthcare providers should educate themselves regarding the clinical presentation of ehrlichioses and the availability of diagnostic resources in their area.