Borrelia burgdorferi and Babesia microti: efficiency of transmission from reservoirs to vector ticks (Ixodes dammini)

In endemic regions, Peromyscus leucopus, the mouse reservoir of the Lyme disease spirochete (Borrelia burgdorferi) and the piroplasm causing human babesiosis (Babesia microti), is nearly universally infected with both agents. Paradoxically, spirochetal infection is nearly twice as prevalent as is babesial infection in populations of field-collected nymphal Ixodes dammini, the tick vector. In the laboratory, a similarly disproportionate rate of infection was observed among nymphal ticks, feeding as larvae, on either B. burgdorferi- or B. microti-infected mice. Ticks which fed on mice with concurrent spirochetal and babesial infections also exhibited twice the incidence of spirochetal infection over that of the piroplasm. These data suggest that the efficiency of acquisition and transstadial passage of B. burgdorferi and B. microti infection differ by a factor of two. This discrepancy may explain differences observed both in the prevalence of infection in ticks collected in the field, as well as the apparently greater risk of spirochetal infection to humans in endemic areas.     

Absence of spirochaetes (Borrelia burgdorferi) and piroplasms (Babesia microti) in deer ticks (Ixodes dammini) parasitized by chalcid wasps (Hunterellus hookeri)

An entomophagous wasp (Hunterellus hookeri Howard) parasitizes about a third of the host-seeking nymphal Ixodes dammini Spielman et al. ticks on Naushon Island in Massachusetts (U.S.A.) where the agents of Lyme disease (Borrelia burgdorferi Johnson et al.) and human babesiosis (Babesia microti Franca) are enzootic. Following blood-feeding, wasp-parasitized ticks are destroyed by the developing wasp. The prevalence of either human pathogen in host-seeking ticks collected in wasp-infested sites is nearly 40% lower than that found in other sites. Nymphal ticks, collected early in their season of activity, are more frequently parasitized by the wasp and less frequently by the Lyme disease spirochaete than those collected later in the summer. Spirochaetes never infected wasp-infected ticks, and few wasp-infected ticks were concurrently infected by the Babesia piroplasm. Taken together, these correlations indicate that the wasp may render the tick inhospitable to both pathogens. The presence of the wasp may have reduced risk of human infection on the island by either pathogen by as much as a third.     

Enzootic Babesia microti in Maine

Human babesiosis in the northeastern United States caused by Babesia microti (Apicomplexa: Piroplasmida) is mainly reported from coastal New England sites, where deer ticks (Ixodes dammini) are common. However, the piroplasm has been detected in microtine rodents elsewhere in association with I. angustus or other nidicolous ticks, suggesting that the agent is widely distributed but zoonotically significant only where a human-biting "bridge" vector is present. To determine whether this piroplasm may be enzootic in areas where I. dammini is absent, we surveyed small mammals collected from 2 sites in Maine, where I. angustus or I. muris is common but I. dammini is not. Of 43 chipmunks, voles, deer mice, and shrews examined, 3 (6.9, 95% confidence interval 0 to 14.5) were parasitemic, as determined by blood smear or polymerase chain reaction targeting a piroplasm-specific portion of the 18S ribosomal DNA gene. Phylogenetic analysis of the sequenced amplification products demonstrates the presence of 2 forms of B. microti. We conclude that B. microti may be enzootic in the absence of I. dammini but that human risk relates to dense infestations of this human-biting tick.     

The role of Ixodes trianguliceps tick larvae in circulation of Babesia microti in the Middle Urals

The nested PCR method with primers flanking a conserved fragment of the Babesia microti ss-rDNA gene was used to examine 834 larvae of Ixodes trianguliceps ticks engorged to a varying degree, taken off 237 hosts of 12 species (rodents and insectivores). The hosts were collected in southern taiga forests in the lowmountain area of the Middle Urals (Chusovoi District, Perm Province) in 2003–2010. Babesia DNA was detected in 89 (10.7%) larvae from 8 species of small mammals. According to the data obtained by PCR and microscopic methods, either B. microti DNA or the parasites themselves were found in the blood of 45.2% of the mammals. The nucleotide sequences of 15 amplicons of Babesia DNA obtained from larvae of I. trianguliceps ticks and their hosts were identical to those of B. microti available in GenBank. In 13 cases, they were similar to B. microti US-type (a human pathogen) and in two cases (those from I. trianguliceps and from the vole Clethrionomys rufocanus from which it was removed), to B. microti of the Munich strain which is not pathogenic to humans. The duration of feeding on small mammals seems to exert the main influence on the infection rate of I. trianguliceps larvae. The fully engorged larvae contained B. microti DNA more often and usually in greater amounts than those collected during the first days of blood-sucking. The latter usually revealed Babesia DNA in the minimum quantity (< 0.064 ng/μl). According to the data obtained, transovarial transmission of Babesia in I. trianguliceps is unlikely. The processes of horizontal and transstadial transmission appear to be of crucial importance for the functioning of the natural foci of babesiosis.     

The occurrence DNA of Babesia microti in ticks Ixodes ricinus in the forest areas of Szczecin

Babesia microti, an intraerythrocytic protozoan and the etiological agent of human babesiosis, is transmitted by the bite of the tick, Ixodes ricinus. The aim of the present study was to confirm the presence of B. microti by detection of the DNA of these protozoans. The prevalence of B. microti was studied using the PCR method with primers complementary to the gene fragment encoding nuclear small-subunit ribosomal RNA (ss-rDNA). In the course of this study a total of 2095 ticks, Ixodes ricinus, were examined. The mean infection rate was 6.2%. Variable prevalance values were also obtained from six different locations and they were further modified by the seasons of the year. The results confirmed the competence of I. ricinus as a vector of B. microti and that a B. microti-specific PCR can provide a sensitive test for laboratory detection of babesiosis.     

Ultrastructure of spirochetes isolated from Ixodes ricinus and Ixodes dammini

Two strains of Ixodes spirochetes, one isolated in the United States (B31) and the other in Sweden (G25), were examined by electron microscopy. Cells of strain G25 were 11-25 micron long with a wavelength of 2.1-2.4 micron and an amplitude of 0.4 micron. Eleven flagella were inserted subterminally at each end of the cell. Cells of strain B31 were similar but had eleven or seven flagella. Cytoplasmic tubules were not seen in cells of either strain. Although not identical, both strains showed ultrastructural details characteristic of the genus Borrelia.     

Ixodes dammini: evidence for salivary prostacyclin secretion

Pilocarpine-induced saliva of adult Ixodes dammini ticks contained abundant amounts (523 +/- 140 ng/ml, mean +/- SE, n = 14) of 6-keto-PGF1 alpha, the stable degradation product of prostacyclin. This prostaglandin was identified by radioimmunoassay and reversed-phase chromatography. This activity may help tick feeding by preventing host hemostatic reactions, by increasing host blood flow at the tick feeding site, and by preventing leukocyte degranulation.     

Immunodepression in Babesia microti infections.

Infection with the avirulent piroplasm Babesia microti in mice is accompanied by a marked depression in the ability of the mice to mount an immune response to sheep red blood cells. The period of immunodepression begins 3 days after peak parasitaemia and is maximal 4 days later. Thereafter, there is a slow return to normal immune responsiveness, correlated with the gradual disappearance of the parasites from the blood. Both IgM and IgG responses are depressed. Cell-mediated responses as determined by contact sensitivity to oxazolone and allograft survival are apparently unaffected. Phagocytic activity was measured by carbon clearance tests is increased, and is correlated with the parasitaemia.     

Sperm precedence in the deer tick Ixodes dammini

ABSTRACT We determined whether female deer ticks Ixodes dammini Spielman, Clifford, Piesman & Corwin (Acari: Ixodidae) can be inseminated repeatedly and whether sperm from first or second matings take precedence in fertilizing eggs. Such information is essential to the design of attempts to reduce the fertility of these vectors of Lyme disease. Although spermatophores are present in about half of questing female ticks, they are present in virtually all those found on deer; the abundance of males on deer exceeds that of females and copulation is common. Females must be inseminated before commencing the rapid engorgement phase of feeding. Males need not be in attendance during feeding, provided that the female has been inseminated preprandially. Thus, preprandial insemination suffices to stimulate rapid engorgement, but less blood is taken than when the female is perprandially inseminated. Both types of insemination effectively fertilize eggs. Eggs from females sequentially inseminated by irradiated and non irradiated males, were fertilized mainly by sperm from the last male. Cobalt-irradiated males mate effectively and their sperm compete with those of non-irradiated males. Sperm from the second two sequential inseminations fertilize most of the eggs. By infesting deer with such irradiated male I.dammini , the abundance of these vector ticks may effectively be reduced.     

Relative Importance of Ixodes ricinus and Ixodes trianguliceps as Vectors for Anaplasma phagocytophilum and Babesia microti in Field Vole (Microtus agrestis) Populations

The importance of Ixodes ricinus in the transmission of tick-borne pathogens is well recognized in the United Kingdom and across Europe. However, the role of coexisting Ixodes species, such as the widely distributed species Ixodes trianguliceps, as alternative vectors for these pathogens has received little attention. This study aimed to assess the relative importance of I. ricinus and I. trianguliceps in the transmission of Anaplasma phagocytophilum and Babesia microti among United Kingdom field voles (Microtus agrestis), which serve as reservoir hosts for both pathogens. While all instars of I. trianguliceps feed exclusively on small mammals, I. ricinus adults feed primarily on larger hosts such as deer. The abundance of both tick species and pathogen infection prevalence in field voles were monitored at sites surrounded with fencing that excluded deer and at sites where deer were free to roam. As expected, fencing significantly reduced the larval burden of I. ricinus on field voles and the abundance of questing nymphs, but the larval burden of I. trianguliceps was not significantly affected. The prevalence of A. phagocytophilum and B. microti infections was not significantly affected by the presence of fencing, suggesting that I. trianguliceps is their principal vector. The prevalence of nymphal and adult ticks on field voles was also unaffected, indicating that relatively few non-larval I. ricinus ticks feed upon field voles. This study provides compelling evidence for the importance of I. trianguliceps in maintaining these enzootic tick-borne infections, while highlighting the potential for such infections to escape into alternative hosts via I. ricinus.     

Isoenzyme Analysis of Babesia microti Infections in Humans

ABSTRACT. We used high-resolution polyacrylamide gradient gel electrophoresis (PGGE) to separate four babesial enzymes to aid in the identification of two Babesia microti isolates established in hamsters. The isolates were compared to two different hamster passages of the "Gray" strain. All isoenzyme patterns from the two isolates and the "Gray" strain were similar except glucose phosphate isomerase (GPI) from one of the "Gray" strain passages. It showed a polymorphic GPI pattern as opposed to a monomorphic GPI pattern seen in the other "Gray" strain passage and the two isolates. The observed differences suggested (i) that some populations of B. microti are capable of having polymorphic GPI, (ii) that the "Gray" strain originally contained (and may still contain) a heterogenous population of B. microti , and (iii) that the population possessing polymorphic GPI was selected over that with monomorphic GPI. This information was obtained by a PGGE method that eliminated hemoglobin from gels and allowed, for the first time, detection of babesial leucine amino peptidase (LAP) and isocitrate dehydrogenase (IDH). In addition, this method provided molecular weight estimations on babesial GPI, LAP, IDH, and glutamate dehydrogenase (GDH), and it proved useful in the identification and characterization of the B. microti isolates.     

Isoenzyme analysis of Babesia microti infections in humans

We used high-resolution polyacrylamide gradient gel electrophoresis (PGGE) to separate four babesial enzymes to aid in the identification of two Babesia microti isolates established in hamsters. The isolates were compared to two different hamsters passages of the "Gray" strain. All isoenzymes patterns from the two isolates and the "Gray" strain were similar except glucose phosphate isomerase (GPI) from one of the "Gray" strain passages. It showed a polymorphic GPI pattern as opposed to a monomorphic GPI pattern seen in the other "Gray" strain passage and the two isolates. The observed differences suggested that some population of B. microti are capable of having polymorphic GPI, that the "Gray" strain originally contained (and may still contain) a heterogeneous population of B. microti, and that the population possessing polymorphic GPI was selected over that with monomorphic GPI. This information was obtained by a PGGE method that eliminated hemoglobin from gels and allowed, for the first time, detection of babesial leucine amino peptidase (LAP) and isocitrate dehydrogenase (IDH). In addition, this method provided molecular weight estimations on babesial GPI, LAP, IDH, and glutamate dehydrogenase (GDH), and it proved useful in the identification and characterization of the B. microti isolates.     

Babesia bovis, Babesia bigemina, Babesia canis, Babesia microti and Babesia rodhaini: comparison of ribosomal RNA gene organization.

The three ribosomal DNA (rDNA) units have been cloned from an Australian isolate of Babesia bigemina. The organization of the units is very similar to that reported for a Mexican isolate of B. bigemina. In Babesia canis four rDNA units have been identified. Both Babesia rodhaini and Babesia microti contain two different rDNA units. A small number of different rDNA units appears to be a common feature of this group of Protozoa. Restriction enzyme analysis of the rDNA units form these species and B. bovis suggests that the genus Babesia as currently defined does indeed include two distinct groups of organisms namely, B. bovis, B. bigemina and B. canis and B. rodhaini and B. microti.     

The midgut hemolysin of Ixodes dammini (Acari:Ixodidae)

Midgut homogenates of the hard tick, Ixodes dammini, lyse erythrocytes from rabbits, rats, hamsters, and guinea pigs. The activity displays sigmoidal kinetics, has an alkaline pH optimum, and is activated by temperature. Hemolytic activity is lost when homogenates are incubated with trypsin or heated for 1 hr at 60 C. Activity is not detectable in nonfed ticks as well as ticks attached for up to 2 days to a host, but increases during the growth phase of feeding. Such activity is postulated to help the initial process of the blood meal digestion by releasing the contents of erythrocytes for further enzymatic hydrolysis.     

Nymphal Ixodes dammini: models of the temporal abundance patterns.

A difference equation model was developed to explore the sensitivity of the temporal pattern of relative abundance of active, host-seeking nymphal Ixodes dammini. Inputs to the model were the temporal patterns of recruitment of nymphs into the active class, mortality and successful acquisition of hosts by the ticks. Input parameters were varied both in the temporal pattern (shape) and in the cumulative level (summed over the period of activity). The output of the models, the temporal abundance pattern, was examined for (1) overall shape and (2) the timing of the peak abundance of host-seeking nymphs. The shape of the temporal pattern of nymphal abundance was not sensitive to changes in the shape of the functions used as input for host-finding. The time of peak abundance of nymphs is slightly sensitive to changes in the overall level of host-finding and mortality. When more ticks are removed from the active class (host-finding or mortality increasing), the time of the peak abundance of the nymphs shifts earlier. However, this shift is small compared to variation in field data. The general shape of the activity pattern was sensitive to changes in the temporal pattern of recruitment. A left-skewed distribution produced output which most resembles field data. The temporal pattern of nymphs entering the active class is important, and is an area which needs further empirical work.     

Saliva of the tick Ixodes dammini inhibits neutrophil function

Pilocarpine-induced saliva of adult female Ixodes dammini ticks inhibits the function of peritoneal-derived rat neutrophils, as measured by anaphylatoxin-induced aggregation, FMLP-induced granule enzyme secretion, zymosan-induced superoxide secretion, and phagocytosis of Borrelia burgdorferi spirochetes. Inhibition ranged from 40 to 80% when saliva was diluted 20 times into the assay medium. This neutrophil-inhibiting activity of I. dammini saliva may aid in tick feeding and facilitate pathogen transmission.     

Babesia microti: Pathogenesis of parasite of human origin in the hamster

The pathogenesis of the disease in hamsters caused by the first human Babesia isolant, tentatively named Babesia microti, and the immunologic relationship of the organism to Babesia canis were studied. The patent phase of the disease was characterized by severe anemia and marked parasitemia which occurred between the 6th and 41st day following infection. An increase in total white cell count with a neutrophilia, eosinophilia, monocytosis, and lymphocytosis was observed during the patent phase. The patent phase was followed by development of a carrier state. This was demonstrated by relapse following splenectomy 113 days after infection. No statistically significant differences were observed between the serum profiles of infected and noninfected animals during the period monitored. A serologic relationship between B. microti and B. canis was revealed by the use of gel diffusion and indirect fluorescent antibody (IFA) tests. The IFA test was used to monitor serum antibody responses during the patent and carrier phases of the disease. Crossabsorption studies between B. canis and B. microti revealed that the two organisms possess common and specific antigens.