Concurrent positive serology for ehrlichiosis and Lyme disease

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.

Multiparasite communities in animals and humans: frequency, structure and pathogenic significance

Individual humans and animals are subject to infection by a variety of parasites (broadly defined to include viruses, bacteria and other non-protozoan microparasites) at any one time. Multiple parasite infections occur frequently in populations of wild animals as well as in humans from developing countries. In some species and regions, hosts with multiple infections are more common than hosts with either no infection or a single infection. Studies, predominantly on animals, show that a wide variety of environmental and host-dependent factors can influence the structure and dynamics of the communities of parasites that make up these multiple infections. In addition, synergistic and competitive interactions can occur between parasite species, which can influence the likelihood of their successful transmission to other hosts and increase or decrease their overall pathogenic impact. This review summarises aspects of our current knowledge on the frequency of multiparasite infections, the factors which influence them, and their pathogenic significance.

Immunoserologic evidence of coinfection with Borrelia burgdorferi, Babesia microti, and human granulocytic Ehrlichia species in residents of Wisconsin and Minnesota

In Wisconsin and Minnesota, Ixodes scapularis (Ixodes dammini) ticks are the vector of three microorganisms that may cause significant disease in humans and lower mammals. These diseases include Lyme borreliosis, which is caused by Borrelia burgdorferi, babesiosis, which is caused by Babesia microti, and human granulocytic ehrlichiosis (HGE), which is caused by an apparently new species in the genus Ehrlichia. Immunoserologic testing was performed on sera from patients with a diagnosis of one of these diseases to determine if there was evidence of coinfection with one or more of the other agents. Of 96 patients with Lyme borreliosis, 9 (9.4%) demonstrated immunoserologic evidence of coinfection: 5 (5.2%) with the agent of HGE, 2 (2.1%) with B. microti, and 2 (2.1%) with both microorganisms. Of 19 patients diagnosed with HGE, 3 (15.8%) showed immunoserologic evidence of coinfection: 1 (5.3%) with B. burgdorferi, 1 (5.3%) with B. microti, and 1 (5.3%) with both microorganisms. One patient diagnosed with babesiosis was also seropositive for ehrlichiosis. These results provide evidence for coinfection, perhaps explaining the variable manifestations and clinical responses noted in some patients with tick-transmitted diseases. In certain clinical settings, laboratory testing for coinfection is indicated to ensure that appropriate antimicrobial treatment is given.

A case of concurrent Lyme meningitis with ehrlichiosis

We report on a case of concurrent Lyme meningitis and ehrlichiosis in a patient with occupational exposure to ticks as a logger. The patient had a febrile Illness with a reticulate erythematous rash on his upper torso, meningoencephalitis, thrombocytopenia, and hepatitis. Acute and convalescent serologies were consistent with a dual infection with Lyme disease and ehrlichiosis. Ixodes scapularis is the tick that is associated with Lyme disease in our area and this tick has also been reported to harbor the species of Ehrlichia that causes human granulocytic ehrlichiosis. Empiric therapy for both Lyme disease and ehrlichiosis should be considered in any patient suspected of having a tick-borne illness and presenting with signs and symptoms compatible with both infections.