22 research outputs found
Strain Diversity in Major Surface Protein 2 Expression during Tick Transmission of Anaplasma marginale
Specific major surface protein 2 (MSP2) variants are expressed by
Anaplasma marginale
within the tick salivary gland and, following transmission, are expressed during acute rickettsemia. In previous work, we have shown that a restricted pattern of MSP2 variants is expressed in the salivary glands of
Dermacentor andersoni
ticks infected with the South Idaho strain of
A. marginale
. Now we demonstrate that the identical restriction does not apply to two other strains of
A. marginale
, and that different variants are also expressed when the same strain is transmitted by different
Dermacentor
spp. This indicates that antigenic diversity among strains is maintained in tick transmission and may be a significant constraint to MSP2 vaccine development
Strain Composition of the Ehrlichia Anaplasma marginale within Persistently Infected Cattle, a Mammalian Reservoir for Tick Transmission
Tick-borne ehrlichial pathogens of animals and humans require a mammalian reservoir of infection from which ticks acquire the organism for subsequent transmission. In the present study, we examined the strain structure of
Anaplasma marginale
, a genogroup II ehrlichial pathogen, in both an acute outbreak and in persistently infected cattle that serve as a reservoir for tick transmission. Using the
msp1
α genotype as a stable strain marker, only a single genotype was detected in a disease outbreak in a previously uninfected herd. In contrast, a diverse set of genotypes was detected in a persistently infected reservoir herd within a region where
A. marginale
is endemic. Genotypic diversity did not appear to be rapidly generated within an individual animal, because only a single genotype, identical to that of the inoculating strain, was detected at time points up to 2 years after experimental infection, and only a single identical genotype was found in repeat sampling of individual naturally infected cattle. Similarly, only a single genotype, identical to that of the experimentally inoculated St. Maries or South Idaho strain, was identified in the bloodmeal taken by
Dermacentor andersoni
ticks, in the midgut and salivary glands of the infected ticks, and in the blood of acutely infected cattle following tick transmission. The results show that mammalian reservoirs harbor genetically heterogeneous
A. marginale
and suggest that different genotypes are maintained by transmission within the reservoir population
Trypanosoma brucei: continuous cultivation of antigenically stable parasites at 29°C and induction of antigenic variants at 37°C
Restriction of major surface protein 2 (MSP2) variants during tick transmission of the ehrlichia Anaplasma marginale
Anaplasma marginale
is an ehrlichial pathogen of cattle that establishes lifelong persistent infection. Persistence is characterized by rickettsemic cycles in which new
A. marginale
variant types, defined by the sequence of the expressed
msp2
transcripts, emerge. The polymorphic
msp2
transcripts encode structurally distinct MSP2 proteins and result in an antigenically diverse and continually changing
A. marginale
population within the blood. In this manuscript, we used sequence analysis of
msp2
transcripts to show that a restricted repertoire of variant types, designated SGV1 and SGV2, is expressed within the tick salivary gland. The same SGV1 and SGV2 variant types were expressed in ticks regardless of the variant types expressed in the blood of infected cattle at the time of acquisition feeding by the ticks. Importantly, subsequent tick transmission to susceptible cattle resulted in acute rickettsemia composed of organisms expressing only the same SGV1 and SGV2 variant types. This indicates that the
msp2
expressed by organisms within the tick salivary gland predicts the variant type responsible for acute rickettsemia and disease. This restriction of transmitted
A. marginale
variant types, in contrast to the marked diversity within persistently infected cattle, supports development of MSP2 vaccines to prevent acute rickettsemia in tick-transmitted infections
Antigenic Variation of Anaplasma marginale by Expression of MSP2 Mosaics
Anaplasma marginale
is a tick-borne pathogen, one of several closely related ehrlichial organisms that cause disease in animals and humans. These
Ehrlichia
species have complex life cycles that require, in addition to replication and development within the tick vector, evasion of the immune system in order to persist in the mammalian reservoir host. This complexity requires efficient use of the small ehrlichial genome.
A. marginale
and related ehrlichiae express immunoprotective, variable outer membrane proteins that have similar structures and are encoded by polymorphic multigene families. We show here that the major outer membrane protein of
A. marginale
, MSP2, is encoded on a polycistronic mRNA. The genomic expression site for this mRNA is polymorphic and encodes numerous amino acid sequence variants in bloodstream populations of
A. marginale
. A potential mechanism for persistence is segmental gene conversion of the expression site to link hypervariable
msp2
sequences to the promoter and polycistron
Specific Expression of Anaplasma marginale Major Surface Protein 2 Salivary Gland Variants Occurs in the Midgut and Is an Early Event during Tick Transmission
Infectivity of
Anaplasma
spp. develops when infected ticks feed on a mammalian host (transmission feed). Specific
Anaplasma marginale
major surface protein 2 (MSP2) variants are selected for within the tick and are expressed within the salivary glands. The aims of this study were to determine when and where MSP2 variant selection occurs in the tick, how MSP2 expression is regulated in salivary glands of transmission-feeding ticks, and whether the number of
A. marginale
organisms per salivary gland is significantly increased during transmission feeding. The South Idaho strain of
A. marginale
was used, as MSP2 expression is restricted to two variants, SGV1 and SGV2, in
Dermacentor andersoni.
Using Western blot, real-time PCR, and DNA sequencing analyses it was shown that restriction and expression of MSP2 occurs early in the midgut within the first 48 h of the blood meal, when ticks acquire infection.
A. marginale
is present in the tick salivary glands before transmission feeding is initiated, but the
msp2
mRNA and MSP2 protein levels per
A. marginale
organism increase only minimally and transiently in salivary glands of transmission-feeding ticks compared to that of unfed ticks.
A. marginale
numbers per tick increase gradually in salivary glands of both transmission-fed and unfed ticks. It is concluded that MSP2 variant selection is an early event in the tick and that MSP2 variants SGV1 and SGV2 are expressed both in the midgut and salivary glands. While MSP2 may be required for infectivity, there is no strict temporal correlation between MSP2 expression and the development of infectivity
Identification of a Novel Mycoplasma Species from an Oriental White-Backed Vulture (Gyps bengalensis)
An intracellular organism was isolated from the tissues of an Oriental white-backed vulture (Gyps bengalensis) in chicken embryo fibroblast cell cultures. Biochemical and physical properties, ultrastructural features, and 16S ribosomal DNA sequencing classified this organism as a new taxon of mycoplasma, for which the name “Mycoplasma vulturii” is proposed