 |
NSW Arbovirus Surveillance & Vector Monitoring Program |  |
|
NSW Arbovirus Surveillance & Vector Monitoring Program | |
 1998 - 1999
Annual Report  |
Methods. Mosquitoes were collected overnight in dry-ice
baited EVS type traps. They were then sent live in cool humid eskies via overnight
couriers to the Department of Medical Entomology at Westmead Hospital for identification
and processing for arbovirus isolation. The mosquitoes were identified according to keys
and illustrations in:
'Mosquitoes and Mosquito-borne Disease in Southeastern Australia' (Russell,
1993),
'A Colour
Photo Atlas of Mosquitoes of Southeastern Australia' (Russell, 1996),
'The Mosquitoes of Victoria' (Dobrotworsky, 1965), and
The twelve volume series 'The Culicidae of the Australasian Region' (Lee et
al., 1980 - 1989; Debenham et al. 1989).
Due to the many
factors that influence mosquito abundance it can be extremely difficult to describe and
compare the population size of particular mosquito species between locations and seasons.
Thus mosquito abundances are best described in relative terms, and in keeping with the
terminology from previous reports, mosquito numbers are depicted as:
All mosquito
monitoring results (with comments on the collections) were placed onto the NSW Arbovirus
Surveillance Web site, and were generally
available within 1-2 days of receiving the sample into the laboratory. Access to each
location's result is from:
<http://www.arbovirus.health.nsw.gov.au/areas/arbovirus/results/199899results/results.htm>.
A brief summary
of the mosquito collections and virus isolations for each location follows. Complete
mosquito details are available on the web site. A comprehensive list of the isolates is
included below, in the section under 'Arbovirus Isolations'.
Results. Overall, 277,167 mosquitoes
representing 57 species were collected in NSW during the 1998-99 season, Culex
annulirostris was the most abundant and the most important of the inland mosquito
species during the summer months, with Aedes vigilax the most abundant species on the
coast.
INLAND. A total of 150,518 individual mosquitoes, comprising 18 species, was
collected from inland NSW. Culex annulirostris was the most dominant
species trapped at most sites and generally comprised 60-90% of the collections. Anopheles
annulipes was the next most common species. One hundred and four isolates were
made, with 4 Ross River (RR), 68 Sindbis (SIN), 1 Edge Hill (EH), 3 Kunjin (KUN), 1 Kokobera (KOK) and 27 unknowns.
Albury:
the majority of mosquitoes from Albury were trapped at the
Sewage Treatment Works (Site 1). Unusual for the inland, mosquito numbers peaked in
November and were 'high' through December, with Cx. annulirostris numbers well
above average. Populations declined noticeably after late January. No viruses were
isolated.
Bourke:
there was only one week of trapping, thus it was impossible to observe any trends in
mosquito abundance. There were no flavivirus seroconversions in the sentinel chicken
flocks, nor were there any isolates from the mosquitoes.
Deniliquin: trapping
began in late January and numbers up to late March were
generally close to average. No viruses were isolated. There were no flavivirus
seroconversions in the sentinel chicken flocks.
Griffith: there were
three trapping sites for the 1998-99 season, producing 66,214 mosquitoes. Generally, numbers were 'high' throughout December,
'very high' during January to mid-March, and declined thereafter to be 'low' by mid-April.
As with the other southern inland sites, mosquito abundances were well above average in
November, with numbers of Cx. annulirostris at Willbriggie (Site 2) being around ten times greater than
normal. Willbriggie also had some extraordinary collections in January, with one trap
yielding 10,644 mosquitoes. The Griffith mosquitoes yielded 40 arbovirus isolates (3 RR, 20 SIN, 1 EH, 2 KUN, 1 KOK and 13
unknown), this being the second greatest haul of viruses from Griffith for the history of the program. It is worth noting that one of the RR viruses was isolated from mosquitoes collected during the first week
of the 'Program', and in seasons prior to this, there had never been an isolate so early
in the trapping season. There were no flavivirus seroconversions in the sentinel
chicken flocks based at Hanwood and
Barren Box Swamp.
Gunnedah: only four
collections were made from late November to early January, with 'low' numbers trapped. No viruses were isolated.
Leeton:
over one third of all the mosquitoes collected from inland regions were from the two
Leeton sites, with 65,200 mosquitoes trapped and the majority
(55,000) from Almond Rd (Site 2). Collections were 'high' to 'very high' from late
November through to mid-March. One trap in the first week of January collected the
extraordinary number of 17,965 mosquitoes; a record for the 'Program' and for this week, Cx. annulirostris numbers were
an astonishing 34 times greater than the average. There were 58 arboviruses isolated (48 SIN, 1 KUN and 9 unknowns) from
Leeton. This is the highest number obtained during any season for any inland location. In
response to the isolation of Kunjin,
a sentinel chicken flock was established in March and tested weekly until the end of
April. None of the chickens seroconverted.
Menindee: numbers peaked in the first week of November, with Cx. annulirostris generally
around ten times the average through this month. After the 'high' collections in November,
mosquito abundances decreased and remained 'moderate' for most of the season. In contrast
to the other inland locations, Culex
quinquefasciatus was the most commonly trapped
mosquito. One isolate of RR was made
from mosquitoes trapped in early November. There were no flavivirus seroconversions
in the sentinel chicken flocks.
Moree:
trapping from November to January yielded collections that were 'low' to 'moderate'.
However, some collections made in October yielded 'high' numbers and the peak was in last
week of September. No viruses were isolated.
Tamworth: numbers
were generally low throughout the season, although some 'high' collections were made in
early January. No viruses were isolated.
Warren:
intermittent collections yielded 'high' numbers in November from the new site of Tiger Bay
(Site 1). Numbers across the season were mostly 'moderate'. One
unknown virus was isolated from Cx.
annulirostris collected at
Tiger Bay.
Wee
Waa: only three collections were made and these were from early in the season.
'moderate' numbers were mainly trapped. Two unknown viruses were
isolated, both from Cx. annulirostris.
Wentworth: like the
other southern inland locations, Wentworth had 'high' numbers through November and this
was when peak Cx. annulirostris abundance occurred. Numbers
thereafter were 'low' to 'moderate'. Two unknown viruses were isolated, both from Cx.
annulirostris.
COASTAL. There were 108,514
mosquitoes comprising 48 species collected from coastal NSW. Sixteen viruses were
isolated, with 8 RR and 8 unknowns.
Ballina: mosquito numbers were mostly 'moderate' (and below average) up until
February. Thereafter 'high' numbers (around average) were collected for the remainder of
the season. Only small numbers of Ae.vigilax were trapped
and comprised around 2% of the collections. The main species were Aedes funereus,
Aedes
multiplex, Culex orbostiensis and Culex sitiens.
Three unknown viruses were isolated.
Batemans Bay: numbers
were mainly 'low' to 'moderate' throughout the season and well below the long-term
average. Aedes
vigilax was the dominant species. Two RR and one
unknown virus was isolated.
Coffs Harbour: weekly collections were consistently 'low', with the occasional
'moderate' from site 1. Aedes
notoscriptus was the most
common mosquito. No viruses were isolated.
Forster:
collections from the two sites were very different; Green Point (Site 1) had mainly 'low'
numbers with Ae.vigilax and Ae. notoscriptus predominating, while
Tuncurry (Site 2) mostly had 'high' collections (including very early and late in the
season). Coquillettidia linealis
comprised over 70% of the mosquitoes captured from Site 2. The difference relates to the
availability of local breeding sites. One
RR was
isolated at Tuncurry from Culex australicus and there was one
unknown.
Gloucester: collections from Gloucester tended to be 'low' and very few noted
vectors were trapped. Culex
quinquefasciatus comprised
around 80% of the collections. No viruses were isolated.
Gosford: this year's mosquito numbers were slightly lower than previous years.
Empire Bay (Site 3) trapped over half of the Gosford mosquitoes; this was due to the close
proximity to Ae. vigilax breeding
grounds. Numbers were mainly 'high' from Empire Bay through most of the season. The other
sites trapped 'low' to 'moderate' numbers. No viruses were isolated from any of the sites.
Kempsey: collections were mainly 'low' to 'moderate', although Jerseyville
(Site 2) had one week in mid-February with very high numbers. Except for these
collections, numbers were around average. In contrast to previous years, it was the
freshwater mosquitoes, particularly Cx.
annulirostris that
dominated collections. No viruses were isolated.
Maclean: trapping was undertaken over a short period only, and numbers tended
to be 'high' and close to average. Culex sitiens was the
dominant mosquito. No viruses were isolated.
Merimbula: mosquito numbers were 'low' through most of the season and slightly
below average. Aedes notoscriptus was the most
common mosquito. No viruses were isolated.
Narooma: generally collections were 'low', with the occasional 'moderate'
number. Aedes camptorhynchus and Ae. vigilax were the
most abundant mosquitoes. No viruses were isolated.
Newcastle: trapping was undertaken only late in the season. Collections were
'low' to 'moderate' from New Lambton (Site 1) and mainly 'high' from Shortlands Wetlands
(Site 2). Aedes vigilax, Cx. sitiens
and Cq. linealis dominated
the traps. No viruses were isolated.
Nowra: collections were consistently 'low' throughout the season from both
sites, with Ae. notoscriptus being the
most commonly trapped mosquito. No viruses were isolated.
Port
Macquarie: trapping began in late February and numbers were mostly 'high' and
around average. The collections were dominated by Cq.
linealis and Ae. notoscriptus. No viruses
were isolated.
Port Stephens: mosquito
collections were generally 'high' throughout the season for all the sites, although a
series of 'very high' collection were made from January to March at Saltash (Site 2) and
Heatherbrae (Site 5). Above average numbers were recorded for most of the season. The most
common species were Ae. vigilax, Cq.
linealis, Cx. annulirostris and Cx.
orbostiensis. Four RR and three
unknown viruses were isolated.
Taree: collections were well down on last year, with no 'very high'
collections being made as occurred late in the previous season. Numbers were mostly 'low'
to 'moderate' from the Racecourse (Site1) and 'high' from Harrington (Site 2). Coquillettidia linealis, Coquillettidia xanthogaster and Cx.
annulirostris were the
most abundant mosquitoes. No viruses were isolated.
Tathra: mosquito numbers were around average for most of the season and 'low'
to 'moderate'. Culex annulirostris and Ae. notoscriptus were the most frequently captured mosquito. No viruses were isolated.
Tweed Heads: Piggabeen Road (Site 1) had 'low' collections for much of the season,
while Beltana Rd (Site 2) had 'moderate' to 'high' numbers. The main species yielded were Cx. sitiens, Cx. annulirostris and Ae.
notoscriptus. No viruses
were isolated.
Ulladulla:
collections were close to average and 'moderate' for much of the season. None of the
collections were dominated by noted vectors, rather Culex molestus and Ae. notoscriptus constituted the
majority of the traps.
Wyong:
numbers were down on the previous season and mostly 'low'. The exception to this was
Ourimbah (Site 5), which consistently had 'high' collections, and around 95% of the
collection was Ae. notoscriptus. One RR was isolated
from Ourimbah.
METROPOLITAN
SYDNEY. A total of
18,135 mosquitoes, comprising 27 species, was collected from metropolitan Sydney. Two
viruses were isolated from the monitoring locations; one RR from Hawkesbury and one STR from Parramatta. An additional four viruses (1
RR, 3 STR) were isolated from other locations within the
Sydney region; these are listed in the table of the Coastal and Sydney Arbovirus Isolates below.
Parramatta: numbers were considerably down on the previous year, which was due to the increased insecticide treatment of Ae. vigilax breeding sites at Homebush Bay. Numbers varied between 'low' and 'moderate', with some 'high' collections made through January and February. The collections comprised mostly of Ae. vigilax and Ae. notoscriptus. One STR was isolated at Pennant Pde from Ae. notoscriptus.
Penrith: collections were mostly 'low' throughout the season at all trapping
sites. The only exception being some 'high' numbers from the Sewerage Treatment Works
(Site 1) in late March. Culex
quinquefasciatus and Ae. notoscriptus were the
most common mosquitoes captured. No viruses were isolated.
Pittwater: 'low' numbers were collected throughout the entire season. The
majority of the mosquitoes trapped were Ae.
notoscriptus. No viruses
were isolated.
