Antigenic and genetic heterogeneity of Borrelia burgdorferi populations transmitted by ticks.
(9/145)
The genome of Borrelia burgdorferi encodes a large number of lipoproteins, many of which are expressed only at certain stages of the spirochete's life cycle. In the current study we describe the B. burgdorferi population structure with respect to the production of two lipoproteins [outer surface protein A (OspA) and outer surface protein C (OspC)] during transmission from the tick vector to the mammalian host. Before the blood meal, the bacteria in the tick were a homogeneous population that mainly produced OspA only. During the blood meal, the population became more heterogeneous; many bacteria produced both OspA and OspC, whereas others produced only a single Osp and a few produced neither Osp. From the heterogeneous spirochetal population in the gut, a subset depleted of OspA entered the salivary glands and stably infected the host at time points >53 hr into the blood meal. We also examined genetic heterogeneity at the B. burgdorferi vlsE locus before and during the blood meal. In unfed ticks, the vlsE locus was stable and one predominant and two minor alleles were detected. During the blood meal, multiple vlsE alleles were observed in the tick. Tick feeding may increase recombination at the vlsE locus or selectively amplify rare vlsE alleles present in unfed ticks. On the basis of our data we propose a model, which is different from the established model for B. burgdorferi transmission. Implicit in our model is the concept that tick transmission converts a homogeneous spirochete population into a heterogeneous population that is poised to infect the mammalian host. (+info)
Identification of an IL-2 binding protein in the saliva of the Lyme disease vector tick, Ixodes scapularis.
(10/145)
A potent inhibitor of mitogen-stimulated T cell proliferation exists in the saliva of several species of hard ticks, including the Lyme disease vector tick, Ixodes scapularis. Our characterization of this phenomenon has led to the identification of a possible mechanism for the T cell inhibitory activity of I. scapularis saliva. The T cell inhibitor can overcome stimulation of mouse spleen cells with anti-CD3 mAb; however, a direct and avid interaction with T cells does not appear to be necessary. Tick saliva inhibits a mouse IL-2 capture ELISA, suggesting that a soluble IL-2 binding factor is present in the saliva. This hypothesis was verified by using a direct binding assay in which plate-immobilized tick saliva was shown to bind both mouse and human IL-2. Elimination of the IL-2 binding capacity of saliva in the in vitro assays by trypsin digestion demonstrated that the IL-2 binding factor is a protein. These experiments comprise the first demonstration of the existence of such a secreted IL-2 binding protein from any parasite or pathogen. This arthropod salivary IL-2 binding capacity provides a simple mechanism for the suppression of T cell proliferation as well as for the activity of other immune effector cells that are responsive to IL-2 stimulation. Relevance of the tick T cell inhibitory activity to the human immune system is demonstrated by the ability of tick saliva to inhibit proliferation of human T cells and CTLL-2 cells grown in the presence of human IL-2. (+info)
Catastrophes after crossing species barriers.
(11/145)
Probably the most tragic examples of virus infections that have caused the deaths of many millions of people in the past century were the influenza and AIDS pandemics. These events occurred as a direct result of the introduction of animal viruses into the human population. Similarly, mass mortalities among aquatic and terrestrial mammals were caused by the introduction of viruses into species in which they had not previously been present. It seems paradoxical that at a time when we have managed to control or even eradicate major human virus infections like polio and smallpox we are increasingly confronted with new or newly emerging virus infections of humans and animals. A complex mix of social, technological and ecological changes, and the ability of certain viruses to adapt rapidly to a changing environment, seems to be at the basis of this phenomenon. Extensive diagnostic and surveillance networks, as well as novel vaccine- and antiviral development strategies should provide us with the safeguards to limit its impact. (+info)
Human health improvement in Sub-Saharan Africa through integrated management of arthropod transmitted diseases and natural resources.
(12/145)
A concept of an ecosystem approach to human health improvement in Sub-Saharan Africa is presented here. Three factors mainly affect the physical condition of the human body: the abiotic environment, vector-transmitted diseases, and natural resources. Our concept relies on ecological principles embedded in a social context and identifies three sets of subsystems for study and management: human disease subsystems, natural resource subsystems, and decision-support subsystems. To control human diseases and to secure food from resource subsystems including livestock or crops, integrated preventive approaches are preferred over exclusively curative and sectorial approaches. Environmental sustainability - the basis for managing matter and water flows - contributes to a healthy human environment and constitutes the basis for social sustainability. For planning and implementation of the human health improvement scheme, participatory decision-support subsystems adapted to the local conditions need to be designed through institutional arrangements. The applicability of this scheme is demonstrated in urban and rural Ethiopia. (+info)
Identification of newly isolated Babesia parasites from cattle in Korea by using the Bo-RBC-SCID mice.
(13/145)
Attempts were made to isolate and identify Korean bovine Babesia parasite. Blood samples were collected from Holstein cows in Korea, and Babesia parasites were propagated in SCID mice with circulating bovine red blood cells for isolation. The isolate was then antigenically and genotypically compared with several Japanese isolates. The Korean parasite was found to be nearly identical to the Oshima strain isolated from Japanese cattle, which was recently designated as Babesia ovata oshimensis n. var. Haemaphysalis longicornis was the most probable tick species that transmitted the parasite. (+info)
Diagnosis of epizootic bovine abortion in Nevada and identification of the vector.
(14/145)
In the 43 years since the first description in California, epizootic bovine abortion (EBA) has been considered but not definitively diagnosed as a cause of late-term abortions on Nevada ranches. Examination of aborted full-term bovine fetuses obtained from Nevada ranches revealed gross abnormalities consistent with EBA (enlarged lymph nodes, petechial hemorrhages of the oral mucosa and conjunctiva, ascites, and splenohepatomegaly), and EBA was confirmed by histologic examination of fetal tissues. The histologic thymic changes were characteristic of EBA and included severe histocytic thymusitis with depletion of thymocytes, interlobular hemorrhage, and fibrinocellular exudation. The gross enlargement of lymph nodes was the result of cortical follicular hyperplasia and histiocytic lymphadenitis. In addition, widespread, predominately nonsuppurative histologic lesions typical of EBA were observed in most organs, including the brain, lung, heart, liver, and spleen. Furthermore, the presence of Ornithodorus coriaceus, the argasid tick vector of EBA, was established by tick collection using CO2 traps. The tick was identified on ranches and in geographic areas (northern and northwestern counties of Nevada) coincident with diagnosis of multiple cases of EBA. This study establishes the presence of EBA as a cause of late-term abortion in Nevada. Additionally, identification of the EBA tick vector, O. coriaceus, in the same areas as the abortions provides strong evidence that the disease is endemic. (+info)
Entomologic and serologic evidence of zoonotic transmission of Babesia microti, eastern Switzerland.
(15/145)
We evaluated human risk for infection with Babesia microti at a site in eastern Switzerland where several B. microti-infected nymphal Ixodes ricinus ticks had been found. DNA from pooled nymphal ticks amplified by polymerase chain reaction was highly homologous to published B. microti sequences. More ticks carried babesial infection in the lower portion of the rectangular 0.7-ha grid than in the upper (11% vs. 0.8%). In addition, we measured seroprevalence of immunoglobulin (Ig) G antibodies against B. microti antigen in nearby residents. Serum from 1.5% of the 396 human residents of the region reacted to B. microti antigen (>1:64), as determined by indirect immunofluorescence assay (IgG). These observations constitute the first report demonstrating B. microti in a human-biting vector, associated with evidence of human exposure to this agent in a European site. (+info)
Cloning of a salivary gland metalloprotease and characterization of gelatinase and fibrin(ogen)lytic activities in the saliva of the Lyme disease tick vector Ixodes scapularis.
(16/145)
The full-length sequence of tick salivary gland cDNA coding for a protein similar to metalloproteases (MP) of the reprolysin family is reported. The Ixodes scapularis MP is a 488 amino acid (aa) protein containing pre- and pro-enzyme domains, the zinc-binding motif HExxHxxGxxH common to metalloproteases, and a cysteine-rich region. In addition, the predicted amino-terminal sequences of I. scapularis MPs were found by Edman degradation of PVDF-transferred SDS/PAGE-separated tick saliva proteins, indicating that these putative enzymes are secreted. Furthermore, saliva has a metal-dependent proteolytic activity towards gelatin, fibrin(ogen), and fibronectin, but not collagen or laminin. Accordingly, I. scapularis saliva has a rather specific metalloprotease similar to the hemorrhagic proteases of snake venoms. This is the first description of such activity in tick saliva and its role in tick feeding and Borrelia transmission is discussed. (+info)