Emergence of the ehrlichioses as human health problems

An Ehrlichia strain from a llama (Lama glama) and Llama-associated ticks (Ixodes pacificus)

An ehrlichia was identified in the blood of a diseased llama (lama glama). Sequencing of its 16S rRNA gene showed the ehrlichia to be closely related to members of the Ehrlichia phagocytophila genogroup. The agent was also found in a pool of ticks (Ixodes pacificus) collected at the llama site.

Serologic and molecular detection of granulocytic ehrlichiosis in Rhode Island

A new indirect fluorescent-antibody (IFA) assay with antigen produced in vitro in the human promyelocytic leukemia cell line HL60 was used to identify the first recognized case of human granulocytic ehrlichiosis in Rhode Island. This IFA assay was used to detect granulocytic ehrlichiae in white-footed mice and in a dog inhabiting the area surrounding the patient's residence. Host-seeking Ixodes scapularis ticks found in the same habitat also were infected. I. scapularis ticks collected from other locations were fed on dogs and New Zealand White rabbits to assess the competency of these species as hosts of granulocytotropic Ehrlichia. Tick-induced infections of dogs were confirmed by serologic testing, tissue culture isolation, and PCR amplification, whereas several rabbits seroconverted but were PCR and culture negative. PCR amplification of the 16S rRNA gene and DNA sequencing of the PCR products or culture isolation was used to confirm granulocytic Ehrlichia infections in humans, dogs, white-footed mice, and ticks.

Serological evidence of human granulocytic ehrlichiosis in Norway

Human granulocytic ehriichoisis was first described in 1994. This tick-transmitted illness is increasingly recognized in the USA as well as in Europe in areas where ixodes ticks and Lyme borreliosis are endemic. Blood samples from 58 Norwegian patients with physician-diagnosed Lyme borreliosis were examined for the presence of antibodies to Ehrlichia equi, a surrogate marker of the agent of human granulocytic ehrlichiosis. The results indicated that 10.2% of the patients may have been co-infected with human granulocytic ehrlichiosis and Lyme borreliosis. Human granulocytic ehrlichiosis appears to be established in southern Norway.

Ehrlichia canis-like agent isolated from a man in Venezuela: antigenic and genetic characterization

We report the first isolation and molecular and antigenic characterization of a human ehrlichial species in South America. A retrospective study was performed with serum specimens from 6 children with clinical signs suggestive of human ehrlichiosis and 43 apparently healthy adults who had a close contact with dogs exhibiting clinical signs compatible with canine ehrlichiosis. The evaluation was performed by the indirect fluorescent-antibody assay with Ehrlichia chaffeensis Arkansas, Ehrlichia canis Oklahoma, and Ehrlichia muris antigens. The sera from two apparently healthy humans were positive by the indirect fluorescent-antibody assay for all three antigens. Of the three antigens, samples from humans 1 and 2 showed the highest antibody titers against E. chaffeensis and E. muris, respectively. The remaining serum samples were negative for all three antigens. One year later examination of a blood sample from subject 1 revealed morulae morphologically resembling either E. canis, E. chaffeensis, or E. muris in monocytes in the blood smear. The microorganism, referred to here as Venezuelan human ehrlichia (VHE), was isolated from the blood of this person at 4 days after coculturing isolated blood leukocytes with a dog macrophage cell line (DH82). The organism was also isolated from mice 10 days after intraperitoneal inoculation of blood leukocytes from subject 1. Analysis by electron microscopy showed that the human isolate was ultrastructurally similar to E. canis, E. chaffeensis, and E. muris. When the virulence of VHE in mice was compared with those of E. chaffeensis, E. canis, and E. muris, only VHE and E. muris induced clinical signs in BALB/c mice at 4 and 10 days, respectively, after intraperitoneal inoculation. VHE was reisolated from peritoneal exudate cells of the mice. Only E. chaffeensis- and E. muris-infected mice developed significant splenomegaly. Western immunoblot analysis showed that serum from subject 1 reacted with major proteins of the VHE antigen of 110, 80, 76, 58, 43, 35, and 34 kDa. Human serum against E. chaffeensis reacted strongly with 58-, 54-, 52-, and 40-kDa proteins of the VHE antigen. Anti-E. canis dog serum reacted strongly with 26- and 24-kDa proteins of VHE. In contrast, anti-E. sennetsu rabbit and anti-E. muris mouse sera did not react with the VHE antigen. Serum from subject 1 reacted with major proteins of 90, 64, or 47 kDa of the E. chaffeensis, E. canis, and E. muris antigens. This reaction pattern suggests that this serum sample was similar to serum samples from E. chaffeensis-infected human patients in Oklahoma. The base sequence of the 16S rRNA gene of VHE was most closely related to that of E. canis Oklahoma. On the basis of these observations, we suggest that VHE is a new strain or a subspecies of E. canis which may cause asymptomatic persistent infection in humans.