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Northern Territory Department of Health Library Services Historical Collection
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!: 614.4323 WHE 1998
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@HEALTH SERVICES
Northern Territory Government
Integrated Mosquito Control and the Katherine Flood, January 1998
P. I. Whelan
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In: Proceedings of the Third National Conference of the Mosquito Control Association of Australia held at Mercure resort Gold Coast, 23-25 September, 1998
(Supplement to the Bulletin of the Mosquito Control Assoc~ation of Australia, Vol 10, No 3, 1998)
For more information contact:
Territory Health Services Medical Entomology Branch PO Box 40596
Casuarina NT 0811
Telephone: 08 89228333 Fax: 08 89228820
Email: peter. whelan@casrdh. health. nt. gov. au
Integrated Mosquito Control and the Katherine Flood, January 1998
1.0 Introduction
Peter Whelan, Medical Entomology Branch, Territory Health Services, Darwin NT.
Katherine is a small inland regional town (population 1-1,000) on the Katherine River, 280 1an south of Darwin in the Northern Territory. On the 26th January (Australia Day) 1998 followjng very heavy rainfall, the Katherine River began flooding the· town and by the following afternoon _reached record l"evels. The Central Business District (CBD) and most of the older residential section of the town was flooded by up to 2 metres of swiftly flowing water, forcing many people from their homes and leaving flooded areas close to the town.
The Territory Health Service (THS) began preparing for a potential mosquito pest problem and an associated outbreak of mosquito borne disease in the Katherine area as soon as the flooding was reported.
This paper outlines the various elements of an integrated mosquito control program in Katherine, involving public awareness, larval mosquito control, adult mosquito control and engineering control methods. The program has provided a number of lessons for improved mosquito control following floods which are applicable to other areas in Australia.
2.0 The Setting
The Katherine River arises in the rocky escarpment of Arnhemland to the north east of the town of Katherine. It th~n passes through the Katherine Gorge as it drops out of the escarpment, flowing past Katherine approximately 15 kilometres downstream on its way to the Daly River and ultimately to the Joseph Bonaparte Gulf.
The Katherine River responds quickly to heavy rainfall in the catchment and can rise over 20 metres or more near Katherine within one day of heavy rainfall in the catchment. During an average 'Wet' season the waters of the river are usually contained within the river levee but there have been past occasions when the waters have exceeded the normal constraining banks.
Flood episodes in 1940 and 1957 flooded the town area, but the floodwaters rose only gradually and the then much smaller town was only shallowly flooded.
The present CBD and the older residential areas of Katherine are situated along the south east bank of the Katherine River (Fig. 1). There is a smali/industrial area on the south west end of the residential area, with the main industrial area at the south east side of the town. The main Stuart Highway from Alice Springs to Darwin crosses the river via the Katherine High Level Bridge and bisects the older sections of the town. There is a rural residential area, the power house, and a small industrial area on the north west side of the river.
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A newer residential area, Katherine East, lies approximately one kilometre south east of the High Level Bridge, separatedJrom the older section of the town by a lower flood prone area which carries the major storm water and sewage systems. On the south west side of the town approximately 2 to 5 kilometres downstream of the High Level Bridge and in geographic order, are the meatworks, the town dump, the sewage treatment works, and a large commercial dairy with associated waste water ponds (Fig 1 ).
Katherine is situated in a limestone area and there are a number of internally draining depressions at various points near the residential areas, resulting from past subsidence of cavernous limestone. Most of these depressions are not flooded under normal 'Wet' season conditions.
The RAAF base of Tindal is approximately 15 km south east of the town and has a considerable range of mess, accommodation and hospital facilities.
Seasonal cases of Ross River virus (RR V) disease and occasional cases of Australian Encephalitis (AE) occur in the Katherine area. The RRV disease case numbers average 30 per year and peak in January to March each year. Four cases of AE have occurred in the Katherine area, with all cases reported in the March to May period. The sentinel chickens in Katherine, which provide an early warning for AE, first sere convert around March, indicating that AE transmission probably occurs as early as February in the Katherine area.
3.0 Routine Mosquito Monitoring and Control in Katherine.
Mosquito monitoring and control in Katherine is part of the Northern Territory Disease Control Program (NTDCP) coordinated by the M~dical Entomology Branch (MEB) of THS.
The NTDCP is an NT wide program designed to assist local government with routine mosquito monitoring_and cop.trol to prevent mosquito borne disease.
Adult mosquito monitoring in Katherine is carried out fortnightly using carbon dioxide (CO2) baited traps. The traps are set at 4 sites near the major sources of mosquitoes which are associated with waste water storage and disposal. The traps are set by a local THS officer and the collected mosquitoes are sent to the :MEB in Darwin for identification and comment.
Larval surveys of potential mosquito breeding sites are conducted fortnightly by the THS officer and the collected larvae are also forwarded to the MEB. The identification of collected mosquitoes, together with comments on the results and control advice, are forwarded to the regional Environmental Health Officer (EHO) in Katherine within two days of receipt by the MEB. The EHO in Katherine then liases with local bop.ies on requests for mosquito control, including the Katherine Town Council on town dr~ins; the local Power .and Water Authority (PA WA) officer with regard to the sewage ponds, and private land owners and businesses for problems with waste water treatment and disposal areas.
Mosquito control by the Katherine Town Council in general is limited to regular fortnightly applications of larvicide to the storm water drain system. Larval control of the other major mcaa98\kathpap\conf
mosquito breeding sites is carried out by ground application of larvicides organised by the land owners or responsible authority after advice from the local EHO. Larvicide applications are carried out either by the land owners or by a contracted pest control company.
The MEB carries out occasional intensive surveys of particular mosquito problem areas in Katherine when request~d by the local EHO or after discussion on particular problems arising from the surveillance program. There is no routine adult mosquito control in Katherine.
W eedicide application to the various waste water storage and treatment ponds are generally carried out after requests by the EHO rather than a routine maintenance program by the various landowners or responsible authorities.
4.0 The Flood
On the evening of the 26 January 1998 the catchment of the Katherine River and the town received very heavy rainfall and the river adjacent to the town began rising above the confines of the banks.
The rising river completely overflowed the banks and reached a record level. Fast moving floodwater to a height of 2 metres flowed through the CBD and the older residential areas.
The flood swept all loose articles, including garbage bins and household effects, throughout the town and the low lying surrounds. The sewage system within the town and the sewage treatment ponds were completely flooded. The town dump, the meatworks and the dairy waste water ponds were overwhelmed and waste water application areas were flooded.
The town was completely isolated by road access from three directions at various points on the Stuart and the Victoria Highway for up to four days. The power station was partially flooded and the power was cut off for at least four days. Phone services, except for mobile phones, were disrupted. J'he various industrial areas, including rural equipment and chemical suppliers, were flooded.
As the flood rose on the night of 26th January and the following day, people were progressively evacuated from houses and temporary refuges by volunteers, emergency workers and the Defence services. The evacuated residents were taken either to Darwin, to local schools, to friends residences in Katherine East, or to the main evacuation centre in a YMCA hall between the town and Katherine East. Katherine East and the Tindal RAAF base were not flooded. People at the evacuation centre were accommodated on stretchers inside the YMCA hall and in Defence tents in the parking lot outside. The tents and the hall were not mosquito proof.
5.0 Immediate Aftermath of the Flood
Katherine was declared a disaster area the day after the flood and the NT government set up a Disaster Council in Katherine to assist flood relief measures. THS set up a regional coordination centre in the upper floor of the mam Government building in the CBD to rncaa98\kathpap\conf
establish coordination between local THS relief efforts, the THS in Danvin, and the Disaster Council.
The initial advice from the MEB in Danvin of potential mosquito problems facing Katherine residents was relayed from the THS Darwin coordination centre to the THS coordination centre in Katherine and then to the local Disaster Council. The MEB began preparation for a mosquito control operatiou. The Environmental Health sections of the RAAF and the Army contacted the MEB with offers of assistance in a control program.
By Friday January 30th the flood waters had receded from the CBD and some flooded areas began ~ining back to the river. The road north was reopened for limited use allowing access for assessment and clean up teams and equipment.
6.0 Organisation of Vector Surveys and Control
A coordinated THS/Defence Force mosquito larval ground survey was planned for 4 days after the flood waters had receded from the CBD. It was thought that mosquito surveys and control operations would not be practical until the Katherine River level had dropped sufficiently to allow the significant flooded areas to drain back into the river. Two days were allowed for the ground surveys and preliminary arrangements before the start of aerial larval control operations. It was thought that mosquito egglaying would not begin until the flood flow had decreased. It was estimated that at least 7 days were required for the hatching of newly laid eggs and subsequent larval development to reach the third instar stage. This·would leave sufficient time to carry out control measures before the larvae pupated, at which stage insecticide treatment would no longer be effective.
The necessary official requests were made for the Defence Environmental Health Units to assist THS, and a Darwin based helicopter was booked for aerial spraying operations. The :ivfEB organised to transport msecticide and other survey and application equipment by road from Danvin. The Anny organised to transport field control equipment from Darwin. MEB staff were immunised for hepatitis and tetanus because of the danger from sewage contaminated areas and debris. Large scale aerial photographs of the Katherine area were obtained and possible areas of flood water retention were assessed.
A disaster code for all expenditure on the Katherine flood was organised by the THS executive, allowing speedy purchase of insecticides, repellents and other consumables with the rninjmum of delay.
The MEB team anived in Katherine on 3rd February. A preliminary inspection of the flooded areas indicated th~t mosquito larvae were p~es~nt. In general the mosquito larvae were relatively young, allowing timely larval control to be carried out before they reached maturity.
Contact was established with the Defence EHO's who had already carried out a limited hand application of insecticide in the immediate vicinity of the evacuation centre.
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A joint TBS/Defence base of operations was established at the Tindal RAAF Base and general planning for vector control was undertaken, including an evaluation of the requirements for insecticides, vehicles, communication equipment, and vector control equipment. A suitable helicopter operational site was approved by the aviation authority on an old disused airstrip near the hospital. A .RAAF tanker was organised for a supply of water for the helicopter.mosquito larval control operations.
Three teams were organised for the larval survey operations, with each team including a MEB staff member. One team, comprising the MEB Senior Medical Entomologist, a THS regional EHO, and a Defence force EHO was designated as the coordinating team. ·Communications between teams was by mobile phone, with the coordinating team liaising by mobile phone to the THS coordination centre. Target survey areas for each team were drawn on sets of small scale (1: 10,000) aerial photographs and the survey results were consolidated onto a large scale (1:40,000) aerial photograph of the general Katherine area.
Public awareness and self protection messages, and requests for additional supplies including repellents, fly control insecticides and other materials, were relayed to the THS coordination centre in Darwin or the THS coordination centre in Katherine.
Trapping for mosquitoes using carbon dioxide baited traps was organised for the evening of 3rd February to allow an assessment of the species, numbers and distribution of the adult mosquito population.
7.0 Public Awareness and Self Protection
The displacement of the people from their houses and their subsequent temporary accommodation in tents meant that many people were potentially exposed to mosquito attack. Significant numbers of adult mosquitoes were detected by the initial CO2 trapping (Figure 3), which indicated a potential for the transmission of arboviruses such as Ross River virus, Barmah Forest virus, Kunjin and Murray Valley Encephalitis.
Radio messages were broadcast during the first two weeks after the flood, warning of the possibility of mosquito attack, the . risk of mosquito borne disease, and advice on self protection measures including the use of repellents. Mosquito repellents were distributed at the emergency evacuation centre.
A public health hotline manned by an EHO was established in the THS coordination room to answer any questions on mosquito borne disease anq other health inquiries.
The NT News and other print media were not available locally until the 6th February. Radio was the only electronic medium for public health messages to be disseminated and this probably had reduced reception except for car radios. However word of mouth communication, inclucfu?.g advice by the various health and emergency workers, provided warnings and advice on mosquito issues. With the restoration of power and print media after 6th February, Katherine residents were able to receive the general THS television and print mcaa98\.kathpap\conf
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LImedia public health messages regarding mosquito borne diseases and the requirement for self protection.
The THS, in cooperation with the Department of Primary Industry and Fisheries, conducts a sentinel chicken program at major towns to provide an early warning system for mosquito borne disease activity. This program involves the monthly bleeding of each flock of chickens to detect antibodies to viruses such as Kunjin virus and Murray Valley encephalitis virus.
One of the sentinel chicken flocks was situated in· Katherine and had not been affected by the flood. Testing for these sentinel chickens was resumed immediately after the flood, with the initial results indicting no evidence of local Australian Encephalitis transmission.
8.0 Mosquito Larval Surveys 3rd-5th February
The initial larval surveys were carried out late on the 3rd February in the rural area south of the town. The combined organised larval surveys were conducted in and around the town area from 4-5th February. The survey teams used four wheel drive vehicles to access designated areas of potential flooding. Larval surveys of prospective sites began with a visual assessment of the potential larval habitats and a detailed survey of all types of habitats in the flooded area Transects were made across large shallow areas and edge surveys were carried out around the margins oflarge flooded areas. Four wheel drive All Terrain Bikes were used to traverse the larger flooded or inaccessible areas.
Larval surveys were carried out using a ladle, with collected larvae transferred to plastic sample jars. Records for each collection included the average number of larvae per dip, habitat type and the growth stages of the larvae. Individualteams delineated mosquito breeding and flooded areas on to their 1: 10,000 aerial photos. This information was then transferr~d to the 1 :40,000 vector control aerial photo as the field teams reported their assessments to the coordinating team.. Larval surveys in the initial period were confined to 5 Ian around the town. Priority areas included the evacuation centre, the broad flooded area between Katherine and Katherine East, and the waste water treatment ponds at the meatworks and the sewage treatment works.
The results of the adult mosquito trapping indicated various areas to be prioritized for increased larval surveys.
9.0 Results of the Larval Surveys 3rd-5th February
The larval surveys indicated that the flooded areas upstream from the town had little mosquito breeding. Generally flooding in these areas· was open and shallow, with sparse grass, and did not receive run off from urbanised areas.
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Areas within the town area and downstream of the town area contained large amounts of mosquito breeding. The larvae were almost exclusively Culex annulirostris ( the common banded mosquito). Most of the larvae present were third and fourth instars, while a few areas had some late fourth instars and pupae present. The density of larvae in some areas were relatively low, from 4 to 5 larvae per dip, while in a number of sites there were relatively large densities of up to 100 l~ae per dip.
The highest concentrations of larvae were found in waste water storage areas or areas subject to contamination by waste water treatment areas, including the meatworks, the sewage ponds, and flooded areas within or downstream of the town area. There was evidence of organic contmp.ination from the sewage system into low lying depressions and the storm water drainage system. The main storm water drain south west of the town had large amounts of black organic sediment on the bottom of the drain. Some late fourth instar larvae and pupae were present in grassy shallow open water adjacent to the evacuation centre.
Most of the mosquito breeding was in discrete flooded areas. There was little flow of water between the various flooded areas or back to the Katherine River or the storm water drainage system. Most of the breeding sites were relatively shallow, (100-200 mm deep), with the highest concentrations of larvae ( 100 larvae per dip) associated with thi~k grass growth. In the deeper depressions (200-600 mm) between Katherine and Katherine East, relatively heavy breeding was associated with emergent clumps of taller grass and partially decomposing submerged grass. The locations of the main mosquito breeding areas are shown in Figure 1.
11.0 Aerial Larval Control Operations 5th-6th February
One of the survey teams was assigned to the helicopter mosquito control operation, while the other two teams continued, ground surveys The helicopter arrived on the afternoon of 5th February and the first attempt at aerial application of insecticide was made soon afterwards in the area between Katherine and Katherine East, near the evacuation centre. However relatively high winds (10-15 knots) forced the cancellation of the spraying soon after starting.
The aerial larval control operation recommenced the following morning when wind conditions were much more favourable. The control operation was preceded by an aerial reconnaissance to familiarise the pilot with the areas requiring treatment. Control areas were deliniated using the 1: 10,000 and 1 :40,000 aerial photos. Priority areas for spraying were near the evacuation centre, the golf course, the sewage ponds, the meatworks and the dump.
The spraying was carried out using a Bell Jet Ranger equipped with boom sprays, T-nozzles (40 kilopascals pressure) and a 400L belly tank, An 800L mixing tank equipped with a motorised pump was used to mix and pump the insecticide solution to the helicopter.
Approximately 30L of BTI concentrate was mixed with 800L of water in the mixing tank.
BTI insecticide (Cybate,1200 IU) was applied at a target application rate of l.7L per ha, and a projected spraying coverage of 9 ha for each 400L helicopter load. Spraying began at 7am
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and carried through uninterrupted until 1 :30pm. Approximately 225 ha was sprayed using 380L ofBTI product.
12.0 Ground Larval Control Operations 5th-6th February
The ground larval control operations were earned out using motorised backpack machines applying BTI (Cybate) or temephos (Abate) 50% EC. BTI was applied where larval were mid fourth instars or younger, while the Abate was only used in areas where late fourth instars or pupae were present. The main areas of ground control were earned out where helicop~er control operations were restricted, such as adjacent to the evacuation centre, the golf club house, occupied residential areas, the power house, and breeding sites adjacent to the Stuart Highway where traffic and engineering operations were under way.
13.0 Engineering Operations
During the ground surveys it became evident that certain areas of ponding could be drained or significantly reduced by simple engineering measures. Drainage of a very large ( 60 ha) area near the Evacuation Centre was being restricted by the raised embankment of the Stuart Highway.
On the evening of 4th February the Stuart Highway was closed by the Transport and Works Department and a 700 mm drainage pipe was installed under the road during the night, after requests by :MEB were forwarded from the THS cordination centre to the Disaster Council..
By the following morning there was considerable flow from east to west through the pipe but further drainage was restricted by an old railway embankment. Additional excavations were carried out through the embankment to allow this water to drain. This measure reduced the flooded area near the e~acuation centre by approximately 300 mm in depth and approximately 50% in area over a two day period.
Other drainage work was carried out to drain a large flooded area between the northern residential side of Katherine and Katherine East. Accumulated silt and gravel on the downstream side of a road culvert was cleared by the Katherine Town Council and resulted in a considerable reduction in the upstream flooded area. Further floodwater reduction was carried out at the meatworks site where waste water was discharging from the waste water storage ponds and flooding an area of pasture. The drainage pipe from the ponds was blocked, and the flooded pasture area was dry after 2 days.
14.0 Adult Fogging Operations
Adult fogging operations were carried out on the 5th and 6th February using the THS trailer mounted LECO HD fogger. The evacuation centre was earmarked as a priority area for adult fogging operations, but unfavourable wind speed and direction on the afternoon of the 5th February meant that the operation had to be suspended. The fogging operation was then
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switched to the sewage ponds area as adult emergence had already begun there in a localised area. The fogging operation in the sewage pond areas was carried out between 6:45 pm and 8:30 pm. Bioresmethrin (Reslin) insecticide mixed 50/50 with diesel was used at the flow rate of 160 mL/min with a vehicle speed of approximately 5 km/hr.
On the following night .(6th February) the winds were favourable for fogging breeding sites near the town. The evaeuation centre area and the flooded and dense vegetation area south of the evacuation centre were fogged.
15.0: Larval Survev 12th February
The MEB returned to Katherine one week after the initial control operation to carry out a follow up larval survey to determine if additional aerial control was required. Toe follow up larval survey was facilitated with the availability of post flood aerial photos and further adult mosquito trap data from various locations. The ground survey was preceded by an aerial inspection of the Katherine town area on the morning of 12th February. The remaining water concentrations were mapped on the large aerial photograph.
Ground surveys were carried out progressively on the morning of 12th February. Mosquito breeding was located in most of the remaining flooded areas. Priority areas for inspection and treatment included the evacuation centre, the golf course, Springvale Homestead, the sewage ponds, the meatworks, Hickeys Lake and the Killarno area. Culex annulirostris was again the predominant species present and all larvae were third to fourth instars. No pupae were present, indicating that the previous control operations had been successful and that the breeding sites inspected had not produced any new adult mosquitoes. Concentrations of larvae were relatively high with up to 40 larvae per dip over considerable areas, with higher concentrations in a number of areas with thick grass.
16.0 Aerial Control 12th February
The follow up aerial control was carried out between 8:30 and 11:30 am on Thursday 12th February. A private contractor supplied the water tanker and MEB staff carried out the insecticide mixing and loading for the helicopter operation. During this operation 120 ha was sprayed, using 200L of BTI. with a target application rate of 1. 7L/ha.
After the aerial control operation around Katherine, aerial inspections and helicopter larval control operations were carried out at Burunga, and Beswick Aboriginal communities, approximately 70 and 100 kilometres respec~vely south east of Katherine. These communities had been flooded and EHO's had reported flooded sewage treatment ponds. The sewage ponds and the sewage ponds overflow areas were specifically targeted for treatment.
These operations took approximately 1.5 hours.
On return to Katherine, the ground· survey team indicated that additional areas at Hickeys Lake and the Springvale area required spraying. These areas were sprayed between 1300 and
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1400 hours. The post spray evaluation indicated good control. The MEB leader held a de- briefing seminar with the local THS staff, and the MEB team returned to Darwin.
17.0 Adult Mosquito Monitoring Results
The results of the adult mosquito trapping at the sewerage pond site for 1997 and 1998 are shown in Figures 2 and 3 respectively. Low to moderate numbers of Culex annulirostris were present just before the flood and rose to a peak four days after the flood (Fig. 3). The numbers of Cx. annulirostris before the flood in January 1998 were significantly higher than the pre~eding year (Fig. 2), indicating that local breeding conditions for this' species were more favourable than the previous year. Most of the adult mosquitoes present in the week after the flood were probably the result of emergence from breeding sites before the flood. By two weeks after the flood, adult numbers had returned to relatively low levels (Fig. 3 ), which were comparable to the previous year (Fig. 2).
18.0 Mosquito Borne Disease Cases
The number of laboratory confirmed cases of RR V disease in the Katherine District from January-June 1997 and 1998 are shown in Figure 3. The number of cases during January and February in the flood year was lower than the previous year, but were higher in March. The March peak however was lower than the peak in February the previous year. The higher numbers in March 1998 could have been due partly to delayed presentations due to the flood, population disruption, and a reduction of available routine medical services. However, it is believed that the indication of less cases in the January to June period for the flood year compared to the previous year probably reflects a real reduction in disease incidence. This reduction can be largely attributed to the success of the Cx. annulirostris larval control measures carried out after ~e flood.
19.0 Aspects That Worked Well
The integrated mosquito control program was a good example of timely intervention that reduced the incidence of disease. One of the prime ingredients for successful control operations was the availability of an experienced and well equipped 11EB team with available resources ready to respond quickly. In addition the speedy reaction and cooperation of the Defence forces, with assistance with personnel, the availability of a base for operations, and field control equipment, was very important in the con~ol program.
The availability and cooperative attitude of COIIllI\ercial enterprises was also essential to the control effort. One aspect that was particularly appreciated was tile ability for southern insecticide supply companies to rush orders of additional insecticides to Darwin. The local availability of a commercial water tanker for the second phase of the control program was also vital, as emergency assistance by the· Defence forces was not available after the initial
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emergency period. Other private businesses involved with the draining operations were also very important.
The availability of the helicopter equipped for insecticide application, and pilots with spray licences and experience with survey and control for mosquitoes, was of utmost importance in these operations. Effective larval control could not have been achieved without the cooperation of the helicopter company. The ability of the helicopter to carry out these op·erations would probably not have been possible without a routine and ongoing MEB aerial mosquito control program in Darwin.
The: :formation of a Disaster Council and having a THS Coordination Centre were very important factors in coordinating supplies and services.
The supply of insecticide and other equipment required by MEB was greatly enhanced by - having a designated cost code for the flood disaster. This allowed speedy purchase of essential supplies.
The organisation of the ground teams into separate teams and a coordinating team, and the use of mobile phones for communications was also invaluable.
The use of aerial photographs of localities and the overall area for delineating the flooded areas was extremely useful. This facilitated the ground surveys, as well as allowing a clear demarcation of the areas to be sprayed as an aid for the pilot.
20.0 Aspects for Improvement
One of the main lessons from the operation was that the number of days from the flooding to the start of mosquito breeding was relatively short. By the start of the larval survey operations, at least some flooded areas had early fourth instar larvae present (7 days after the flood waters had reached a maximum), indicating that eggs had been laid in some areas one or two days after the flood reached the maximum flood extent. The time of development from egg laying to 4th instar was as little as 7 days. This is shorter than expected and may have been due to the high temperatures and the lack of cloud cover in Katherine at the time. Larval surveys should be carried out a maximum of 4 days after the floodwaters stabilise and within 5 days of initial flooding in areas with relatively high temperatures.
The larval survey operations could have been greatly assisted by having a helicopter on hand for the initial survey to allow a quicker assessment of the flooded area and faster ground surveys with less personnel. The helicopter could have been used to access some of the more inaccessible areas for the ground survey persc;mnel. Two helicopters would have been ideal, with one transferring ground survey teams and the other to carry out spray operations.
The availability of new flood photos on a daily basis after the flood and before the ground surveys would have assisted the surveys and the aerial application. The flood photos were available during the second phase of the control operations, but they were of limited use mcaa9 8\kathpap \conf
becall:se they showed the maximum extent of the flooding, rather than the remnant pools. It is necessary to have post flood photos from at least three or four days after the maximum flood.
The selection of the site for the evacuation centre :-Vithin the flood area, while suitable for evacuation purposes, did hinder the aerial control operations. Time consuming hand control had to be carried out around the evacuation centre to avoid spraying people.
Local vector control equipment and insecticide supplies were not available. While it is not necessary to have all the requirements for a di~!ster on hand, minimum hand control equipment and a small supply of a range of insecticides should be stocked in a ,secure area for small c?ntrol operations, until the larger requirements are assessed.
One vital limiting factor for the control program was the lack of availability of suitably trained local personnel for vector surveys and control. In the initial stages, local EHO'S were tied up with flood relief and food premises duties. The local EHO and other THS officer with experience of vector control and surveys assigned to the control teams were invaluable with their local knowledge and contacts. More local officers, particularly with vector and fly control experience would have been beneficial in the initial survey period.
One aspect that became quite clear was that storm drain maintenance of the town drain system had not been carried out in an adequate manner or on a routine basis. This maintenance should have been carried out before each Wet season. If this had been done it would have allowed much more efficient drainage of the remnant flood areas after the initial floodwaters had gone down.
The local council was relatively small and was overloaded with other duties. The council was unable to contribute to the larval survey and control operations, although they did assist with the engineering measures. Local councils however should be organised to carry out basic mosquito survey and control, operations, and be capable of doing this in emergency situations.
A major conclusion from this exercise was the need for urgent and additional flood mitigation measures in Katherine. Those areas within 2 km of the residential areas of Katherine which remained flooded for more than one week after the floods should be either drained or filled so that they are unavailable as mosquito breeding areas. This work is a vital public health measure and is unrelated to flood mitigation measures that may be required to protect property.
21.0 Conclusions
The integrated mosquito control program carried out in Katherine following the Australia Day floods in 1998 was very successful in controlling large flooded areas with high number of Cx. annulirostris larvae. This resulted in a significant reduction of adult mosquitoes for up to three weeks after the flood.
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The reduced number of reported cases of Ross River virus disease indicates that the control was effective in reducing the amount of arbovirus transmission to a level below seasonal expectations. This was a significant achievement in a situation where there were significantly increased areas of mosquito breeding and significant numbers of people exposed to mosquito attack.
This operation was a good example that larval mosquito control, if carried out in a timely and effective manner before a disease transmission starts, can be effective in preventing mosquito borne disease outbreaks.
22.0 Acknowledgments
The following people played an important and vital role in the integrated mosquito control operations in Katherine. These are in alphabetical order:
Flight Lieutenant Robert Blackford, officer in charge Environmental Health Unit, RAAF, Tindal; responsible for cooperation with THS.
Mr Charlie Griffiths, THS officer; involved in mosquito surveys and ground control.
Ms Gwenda Hayes, Mr Ross Nowland, and Ms Jane Carter and of the Medical Entomology Branch; organisation of equipment, field surveys, logistics, identifications and helicopter control operations.
Dr- Shirley Hendy, Public Health, Chief Health Officer, Family and Children's Servicesi Darwin; coordination and support.
Mr Paddy MacDonald, Engineering Section of Transport and W or.ks; Stuart Highway rectification drainage works.
Mr Tony Morley of the Environmental Health Section, Territory Health Services, Katherine;
ground survey and control operation,.
Sergeant Ken Neylon, Environmental Health Section, Army, Robertson Barracks;
coordination of Army personnel and equipment, and member of ground survey and control teams.
Mr Wayne Osborne of the Katherine Town Council; implementation of local drain clearance.
Corporal Jeff Reeves, Environmental Health Unit, RAAF, Tindal; member of a ground survey and control team.
Mr Xavier Schobben, Environmental Health THS, Darwin; coordination at THS coordination centre.
mcaa98\k:athpap\conf
Private Aaron Smith, Environmental Health Section, Robertson Barracks; one of the grourid survey and control team.
Sergeant Jerry Tescavich, Environmental Health Unit, RAAF, Tindal; initial organisation with MEB.
Mr Larry Tessman, Mr Paul Ledbetter and Mr Doug Crossin; pilots for Rotor Services.
Mr John Woollard, Environmental Health, Katherine; THS coordination with Disaster Council.
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Katherine Flooded areas 3 Feb 1998 (8 days after flood)
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Aerial pboeo from DLP&E ::.&11196
• Figure 2:
Adult Mosquito Monitoring Results - Katherine Sewage Ponds 1997
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9-Jan 24-.Jan 7-Feb 21-Feb 7-Mar 21-Mar 4-Apr 18-Apr
Collection Date
