Detection and Identification ofEhrlichia, Borrelia burgdorferi Sensu Lato, andBartonella Species in Dutch Ixodes ricinusTicks
http://jcm.asm.org/content/37/7/2215.full
Door: Leo M. Schouls, Ingrid Van De Pol, Sjoerd G. T. Rijpkema, and Corrie S. Schot
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In the study presented here we used this method to detect and identifyEhrlichia and B. burgdorferi species in DutchI. ricinus ticks. Analysis of the ticks showed an unexpected high rate of infection with Ehrlichia species (45%). The high infection rate may be partly due to the fact that the ticks originated from roe deer, which may serve as a reservoir forEhrlichia. However, there was no significant correlation between sex and engorgement of the ticks and infection withEhrlichia species. In addition, ticks collected from the same roe deer carried a variety of Ehrlichia andBorrelia species. This suggests that the ticks may have been infected before feeding on the roe deer and that theEhrlichia spp. originated from other reservoirs. In order to get a more accurate impression of the prevalence ofEhrlichia infection in Dutch ticks, we are now analyzing a large number of ticks collected from the vegetation. Whatever the reservoir may be, the results obtained in this survey suggest that Dutch ticks may pose a serious health threat to both humans and animals and should be used to warn clinicians to be aware of the possible presence of ehrlichiosis in The Netherlands.
The majority of the Ehrlichia species found in this study belong to the E. phagocytophila group. As expected, neitherE. canis nor E. chaffeensis was found in any of the ticks. Analysis of PCR products revealed that the 16S rRNA gene sequences of the E. phagocytophila group showed slight variations. In total, four types of E. phagocytophila-like sequences were found: species with the E. phagocytophila or the HGE 16S rRNA gene sequences and two variants of these sequences that carried a substitution of a single base pair at position 92 of the 16S rRNA gene. This corroborates the findings of a Swedish group (28) and a group from the United States (2) that also found Ehrlichia species in which the A at position 92 of the 16S gene was substituted by a G. It remains to be determined whether the 16S rRNA variants represent different Ehrlichiaspecies. It is possible that the HGE agent, E. phagocytophila, and the variants found in this study all belong to the same species and should be designated E. phagocytophilasubspecies. Furthermore, it is unclear whether these variants can cause disease in humans or animals. It was remarkable that in none of the samples of the E. phagocytophila group from which the 16S rRNA gene sequences were determined was a C found at position 49 in the 16S rRNA gene. The presence of a C at this position may be characteristic for E. equi. This would corroborate earlier observations that E. equi was not found in Europe.
More than 6% of the ticks were infected with anEhrlichia-like organism not described before. This organism is closely related to but clearly distinct from the monocytic group ofEhrlichia species and C. ruminantium. It is unclear whether this organism can cause disease in mammals, but experimental infection of animals may confirm its infectious nature. The newly identified organism may represent an endosymbiont. Examples of such endosymbionts in ticks are the Francisella andWolbachia species, which are found at high rates in particular tick species (16-18). However, the relatively low frequency of infection of the ticks would argue against this hypothesis.
Analysis of the 121 ticks showed that 13% of the ticks carriedB. burgdorferi species and confirmed earlier findings that 10 to 35% of the Dutch I. ricinus ticks are infected withB. burgdorferi genospecies (24). Interestingly, 5 of the 121 ticks were coinfected with Ehrlichia and two genospecies of B. burgdorferi. Due to its immunosuppressive nature, coinfection with Ehrlichia and B. burgdorferi may increase the severity of Lyme borreliosis.
Transmission of Bartonella species by ticks is speculative. However, at least one study reports on three patients with B. henselae bacteremia. These patients had no history of contact with cats but sustained tick bites prior to the bacteremia (13). From the study presented here it is clear that a large proportion of the ticks carry Bartonella species or species closely related to Bartonella but not the human pathogens B. henselae and B. quintana. The Bartonellaspecies found might originate from small rodents on which the ticks may have been feeding. This could indicate that transmission ofBartonella species between rodents is, at least in some part, tick mediated. Further studies with other arthropods such as body lice and perhaps also blood from rodents such as rats may disclose the reservoirs and vectors for B. quintana.
Until now there have been no reports of ehrlichiosis in Dutch patients. Therefore, the high rate of infection of Dutch ticks withEhrlichia species raises the question of whether human ehrlichiosis does occur in The Netherlands. It is known thatEhrlichia species cause infections in cattle, sheep, and dogs in Europe. However, until now there have been very few reports on human ehrlichiosis in Europe (15, 20, 27). In fact, only recently was the first case of granulocytic ehrlichiosis infection reported, and that was in Slovenia (20). Although the seroprevalence in several European serosurveys suggest that infections with Ehrlichia do occur in Europe, there seems to be a paucity of reported cases. There may be several explanations for this phenomenon. First, it is possible that there really are very few cases of human ehrlichiosis. Second, the majority of cases may go unnoted because they are caused by less virulent variants of HGE that result in a mild course of disease. Finally, cases of ehrlichiosis may remain unnoted because clinicians do not recognize the disease. Relatively few clinicians know that the disease exists and therefore cannot make the correct diagnosis. Furthermore, the tools used to diagnose ehrlichiosis are usually lacking. Very few laboratories in The Netherlands are equipped to perform serology studies for Ehrlichia, and PCR is performed in none of these laboratories. Therefore, at least in The Netherlands, ehrlichiosis may have been overlooked. Recently, a Swedish group reported on three PCR-confirmed cases of HGE infection in humans (PROMED file 980418193622). Two of the three patients were seronegative, which forewarns us that serology may not suffice for the diagnosis of ehrlichiosis. The patients showed a variety of clinical symptoms, of which only fever and headache were seen in all three patients. Remarkably, the initial diagnosis for one of the patients was neuroborreliosis, and the patient was treated for this condition. These findings indicate that HGE infections do occur in Europe and suggest that there may indeed be an underdiagnosis of ehrlichiosis and that surveillance is required to determine the true extent of the problem.
Hoewel ik het wel had besproken destijds met mijn huisarts, en hij noch ja of nee durfde te zeggen, blijft het ondanks dit onderzoek nog steeds heel erg stil in de huisartsen praktijken.
Maar ook de Nederlandse labs. geven geen krimp.
Ik ben zelfs nog nooit getest voor de genospieces van Borrelia in het regulier (mijn huisarts stuurt het bloed naar het Apeldoorns lab.), terwijl die in 35% van deze bijeengebrachte Nederlandse teken voorkwam, en nu na al die jaren is het percentage hoogstwaarschijnlijk nog wel opgelopen.
(gezien er steeds meer besmettingen worden gemeld)