24 research outputs found
Nonrandom Distribution of Vector Ticks (Dermacentor variabilis) Infected by Francisella tularensis
The island of Martha's Vineyard, Massachusetts, is the site of a sustained outbreak of tularemia due to Francisella tularensis tularensis. Dog ticks, Dermacentor variabilis, appear to be critical in the perpetuation of the agent there. Tularemia has long been characterized as an agent of natural focality, stably persisting in characteristic sites of transmission, but this suggestion has never been rigorously tested. Accordingly, we sought to identify a natural focus of transmission of the agent of tularemia by mapping the distribution of PCR-positive ticks. From 2004 to 2007, questing D. variabilis were collected from 85 individual waypoints along a 1.5 km transect in a field site on Martha's Vineyard. The positions of PCR-positive ticks were then mapped using ArcGIS. Cluster analysis identified an area approximately 290 meters in diameter, 9 waypoints, that was significantly more likely to yield PCR-positive ticks (relative risk 3.3, P = 0.001) than the rest of the field site. Genotyping of F. tularensis using variable number tandem repeat (VNTR) analysis on PCR-positive ticks yielded 13 different haplotypes, the vast majority of which was one dominant haplotype. Positive ticks collected in the cluster were 3.4 times (relative risk = 3.4, P<0.0001) more likely to have an uncommon haplotype than those collected elsewhere from the transect. We conclude that we have identified a microfocus where the agent of tularemia stably perpetuates and that this area is where genetic diversity is generated
The Humber Regional Environmental Characterisation
The Humber Regional Environmental Characterisation (REC)
is a multidisciplinary marine study of the geology, biology
and archaeology of an area of 11 000 km2 off the east coast
of England. It was funded by the Marine Aggregate Levy
Sustainability Fund (MALSF).
2. Within the REC area, there are 12 active aggregate licences
with applications submitted for 10 more. Within the region
there is also gas production, wind energy development, and
intensive shellfish harvesting. Without proper management of
the sea bed areas there could be conflict over development of
resources in the area.
3. The overall objective of the REC project was to provide
integrated broadscale seabed maps in order to support the
sustainable management of offshore resources now and into
the future. The basis of the maps is a regional assessment
of the physical, biological and archaeological environment.
Here for the Humber REC area we present the results of each
individual project element together with their integration into a
holistic overview of the marine environment.
4. In addition to SeaZone single beam bathymetry, data from
three geophysical and one sampling survey provided the basis
for the interpretation. BGS legacy data supplemented the
new data set. In total these data provided a sound basis for
reporting on the regional character of the geology, biology and
archaeology of the area.
5. The geology of the Humber REC area is characterised by a
western gravelly region, a sandy eastern one and a transitional
area in between. Outside of large sand banks and areas of
sand waves the mobile sediment cover is thin. The terminations
of the outer Norfolk Banks are located in the southeast of the
area, and a series of low amplitude sinuous and linear banks
are found in the southwest and centre. A number of arcuate and
linear deeps, with a radial pattern incise the seabed.
6. The morphology and sediment distribution are attributed to a
number of episodes; initially the region was glaciated and the
Bolders Bank till Formation was laid down. After deglaciation
the till was eroded to leave a thin coarse-grained relict deposit.
As sea level rose the area was transgressed, the relict deposit
winnowed and fine grained sediment was transported into
the area from the south. This sediment was reworked into the
sand banks and sand waves present today over much of the
sea bed. The dominance of gravelly sediment in the nearshore
areas is the result of strong currents.
7. The Humber REC area is a region which is rich in archaeology,
with finds ranging from the Palaeolithic to World War II. The
archaeological material in the Humber REC region can be found
both on and beneath the seabed. This archaeological material
can be grouped into three main categories, prehistoric, maritime
and aviation, all of which are present within the study area.
8. Several locations of archaeo-environmental potential were
discovered during the Humber REC which directly relate to
the regions prehistoric archaeological potential. Most of this
potential is present in major channel systems within the south
and east of the study area and dates to the Mesolithic period.
9. The submerged prehistoric resource has been characterised.
This has been derived from the spatial mapping for the
Mesolithic period. Evidence for earlier periods of prehistory
is limited within the study area. The characterisation of
the Mesolithic landscape indicates that where suitable
preservation conditions exist there may be a large resource of
material present.
10. The maritime archaeological resource from the late 19th
century onwards can be located across the study area and has
also been spatially mapped and characterised. No evidence
was found for pre 19th century wrecks, despite documentary
evidence indicating their presence.
11. The Humber REC area has also been a focus for aviation
activity, particularly during World War II, and correspondingly,
wrecked aircraft are likely. As most aircraft break up on impact,
the wreckage is not commonly intact and can be hard to
locate. As such, the number of aircraft wreck sites known to
be present within the study area is assumed to represent only
a small proportion of incidents, but are possibly more likely
in areas on routes to and from World War II targets such as
nearby airbases and Kingston upon Hull.
12. Analysis of the biological data collected across the Humber
REC study area revealed four functional biological communities.
13. The most common community ‘infaunal polychaetes with
burrowing bivalves and amphipods’ was recorded across much of
the mid and eastern sections of the study area in sandy deposits.
The second most abundant community was characterised by
‘barnacles, ascidians and tubiculous polychaetes’ and was
associated with coarser, mixed sediments with suitable areas
for attachment. In some areas where the REC study area was
influenced by higher levels of sand this community was replaced
by a ‘Sabellaria spinulosa reef’ community. A small number of
locations, in both mixed and sandy sediments, were found to
support a very sparse biological community.
14. The biological communities were found to correlate strongly
with the composition of sediment deposits, but were also
influenced by shear bed stress and stratification of the water
column. Predicted biotope distributions maps were created
for the Humber REC study area utilising the EUNIS habitat
classification scheme and habitat suitability modelling.
Both methods yielded maps which are suitable for marine
management purposes. However, since the EUNIS scheme
forces a split on a limited set of environmental variables, which
did not correlate strongly with the biological communities, it
was felt that this method led to an overly complicated map with
many communities occurring in multiple habitats.The EUNIS
habitat model and RECHUM functional community model were
combined to create a full coverage biotope model equivalent to
EUNIS Level 5.
15. A number of rare and alien species were identified across the
Humber REC study area including the tiny bivalve Coracuta
obliquata This is only the second record of this species from
British waters in the last 100 years. The invasive American
Slipper limpet was also observed and it is thought that these
records may indicate a northwards shift in the range of this
species, possibly associated with a warming climate.
16. Potentially important Annex I reef habitats were found in
association with the Silver Pit. The reefs were predominantly
created by the Ross worm Sabellaria spinulosa although high
densities of the blue mussel Mytilus edulis were also identified.
It seems likely that there is a cyclical succession occurring
between these two reef building species driven by minor
changes in environmental conditions and recruitment success
Basic Research in Computer Science
This paper introduces new-HOPLA, a concise but powerful language for higherorder nondeterministic processes with name generation. Its origins as a metalanguage for domain theory are sketched but for the most part the paper concentrates on its operational semantics. The language is typed, the type of a process describing the shape of the computation paths it can perform. Its transition semantics, bisimulation, congruence properties and expressive power are explored. Encodings are given of well-known process algebras, including #-calculus, Higher-Order #-calculus and Mobile Ambients