National Disease Control Program Northern Territory report, 1986/87

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HISTORICAL

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NATIONAL DISEASE CONTROL PROGRAM NORTHERN TERRITORY REPORT 1986/87

MEDICAL ENTOMOLOGY BRANCH

N. T. DEPARTMENT OF HEALTH AND COMMUNITY SERVICES

The Northern Territory contributions to the National Disease Contr~l Program have continued to reduce the numbers of insects of medical importance in the Northern Territory. Significant reductions in the area available for mosquito breeding in Darwin have been achieved by engineering means, while chemical and biological insecticide applications in population centres such as Darwin, Alice Springs, Nhulunbuy and Jabiru have reduced the numbers of both pest and potential vector mosquitoes.

Entomological advice on development proposals including rural, residential and industrial projects has ensured that potential mosquito problems have been reduced or avoided. Publicity and awareness campaigns involving the potential effects of mosquitoes have encouraged the people of the Northern Territory to take better self protection and mosquito avoidance measures, while investigations of mosquito activity in the major tourist areas will enable visitors to have a more pleasant and healthy visit to the "outback Territory".

Highlights of the year have been:

DL HIST 614.432

Continued exclusion of Aedes aegypti and thus dengue fever transmission from the Northern Territory.

Continued absence of malaria transmission despite increasing numbers of imported cases.

Improved drainage of mosquito breeding areas at Leanyer and Coconut Grove swamps.

Dramatic reductions in salt marsh mosquito reaching Darwin's northern suburbs due to the schemes and the highly successful helicopter control operations in late 1986.

Successful use technique for in early 1987.

of the helicopter mosquito control of potential arbovirus

numbers drainage mosquito

control vectors

Exotic Mosquito Borne Disease

Aedes aegypti, the dengue fever mosquito, has continued to be excluded from the Northern Territory, due in part to public awareness programs promoted by the Department, and to the co- operative efforts between the Branch and the Commonwealth Quarantine Service. This absence has been confirmed by the special Aedes egg trap surveillance program at points of entry in the Territory, fortnightly checks in each suburb of Darwin, from larval searches of more than one hundred residences along the tourist route from Queensland (where the dengue vector is endemic), and larval and adult surveys around the coast and at various vulnerable towns throughout the Northern Territory. The results of the ovi trap surveillance program in Darwin and suburbs are shown in Table 1.

The continued exclusion of Ae. aegypti is very cost effective as attempts to eradicate or control this vector mosquito in other areas have proven very costly, and have often had l i t t l e success.

The need to keep the Territory free of the vector was highlighted by the notification of an imported case of dengue fever near Darwin this year.

There were twenty confirmed cases of imported malaria in the malaria receptive area of the Northern Territory this year, representing an increase over previous years. All cases were entomologically investigated and cases in Darwin, Adelaide River and Katherine required adult mosquito control measures. Only one of the fifteen Darwin cases required these measures and this is seen as a reflection of the continuing reduction of the numbers of Anopheles farauti and other malaria vectors in the Darwin residential area. However, increased accessability of South-east Asian destinations to Territorians, together with the increasing number of international tourists passing through the Territory, must increase the risk of reintroduction of malaria into the N. T., and i t is vital to maintain vigilance with surveillance and control programs.

Endemic Mosquito Borne Disease

The presence of Ross River virus, the causal agent of epidemic polyarthritis, has again been detected over a wide area of the top end of the Northern Territory. The sixteen serologically confirmed cases, which are set out in detail in Table 2, included cases from East Arnhem, Katherine a~d Darwin regions. Arbovirus diseases are traditionally underreported as the symptoms are often general or subclinical, and these confirmed cases represent only a part of a regular and widespread prevalence of mosquito borne disease in the Northern Territory.

TERRITORY HEALTH SERVICES

The case clustering around Katherine and Borroloola probably represents a combination of high vulnerability and a heightened awareness by local medical practitioners and health authorities.

Personal protection such as insect screening, protective clothing, avoidance of risk locations at certain times, and repellants should be ongoing practices in at least these two communities.

As part of the arbovirus research program, the branch processed 29,518 live mosquitoes, and of those screened by the Virology Unit at the Department of Primary Production so far, virus isolations have been obtained from three species. Table 3 shows the numbers of mosquitoes collected from each location and those which were positive for virus. To establish an understanding of arbovirus transmission and vector abundance this year's collections were from Darwin where Aedes vigilax and Culex annulirostris are major vectors, from Mataranka where Aedes normanensis is a major vector, and from the little-studied Aboriginal communities of Peppimenarti and Palumpa.

Last year there were 22,480 mosquitoes processed and 17 viruses were recovered, including two alphaviruses (Sindbis and Getah) and one flaviviruse (Edge Hill). If, as these results indicate, one in a thousand mosquitoes of a vector species are harbouring arboviruses, many Territorians and visitors must be infected each year.

Distribution of Vectors

The abundance and breeding areas of the vector mosquito species of the Northern Territory can only be determined by frequent and extensive field surveys and by a trapping network operated by local authorities. An ongoing mosquito monitoring program, in conjunction with health surveyors, town councils and mining companies, has provided monthly data for Alice Springs, Nhulunbuy, Katherine and Jabiru. Supplementary surveys to these areas, and surveys along the inland route to Queensland, to the Finniss River region, Batchelor and to Peppimenarti and Palumpa have also been conducted. Identifications of large numbers of mosquitoes collected in the Victoria River Downs district, Wadeye, and Ngukurr in previous years have been completed.

Jabiru continues to have the highest numbers of pest and disease carrying mosquitoes, and these are the subject of regular fogging operations. To maximise the effectiveness of this fogging, officers from the Branch conducted a comprehensive trapping program there and determined the major source of the mosquitoes and the optimum fogging route.

From a study in April of vector and nuisance mosquito species and their breeding areas at Il Parpa swamp in Alice Springs, and from information gathered from monitoring data and previous surveys, a report was prepared advising the council and the Transport and Works Department consultants on ways to manage the sewerage treatment plant and swamp to minimise mosquito breeding.

A mosquito survey of inland towns from Larrimah to the Queensland border and north to Borroloola indicated domestic mosquito breeding at most communities, but that the dengue fever vector, Aedes aegypti, was s t i l l absent. However the area remains highly receptive to its re-introduction. Other important mosquito species were collected in very high numbers in some areas, highlighting the need for mosquito avoidance to be practiced. A number of cases of epidemic polyarthritis were confirmed from Borroloola for this time, and from our survey i t seems that the vector responsible was~ normanensis.

Mosquito breeding at the Aboriginal communities of Peppimenarti and Palumpa was assessed in April. Large numbers of Anopheles mosquitoes were collected at both communities, indicating their receptivity to malaria. The noted arbovirus vector, Culex annulirostris, was also found and the local council advised of a suitable control procedure for one of the significant breeding areas near Peppimenarti. Avoidance was once again the most practical measure for mitigating the health risks posed by mos qui toes.

In anticipation of continued expansion of rural living in the Darwin region an extensive monitoring program was operated in the Darwin River, Berry Springs, Noonamah and Acacia Gap areas. This adds further to the baseline data derived for the Howard Springs and Humpty Doo localities. A study of the biting insects in the Palmerston area is also being conducted to enable advice to be given to planning authorities on ways to minimise potential pest and disease problems.

A preliminary survey of mosquito breeding in the Finniss River district in May indicated several areas of intensive mosquito breeding. This data will be used to assist planning of any proposed developments of the area.

Other important projects include a mosquito monitoring program which was commenced in the rural area in December to gather information on vector species and their abundance in areas being considered for a new army base. A brief survey of the Batchelor area pinpointed mosquito problems resulting from effluent from the sewerage treatment works and abattoir, and from a disused dam.

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The Integrated Control of Mosquitoes

The principal mosquito problem associated with Darwin's coastal swamps has been plagues of the saltmarsh mosquito, ~ viqilax.

A drainage program, carried out in conjunction with the Darwin City Council and the Northern ·~Territory Government has significantly reduced mosquito breeding areas of all species in Leanyer Swamp. This is demonstrated in pie charts shown in Table 4.

To control mosquitoes in areas of Leanyer Swamp that couldn't be drained and in the less accesible extensive swamps of Holmes Jungle, Micketts Creek and on RAAF land, a helicopter was used to apply a biological insecticide. This technique was very successful in October when trialled on a 30 hectare site which had been turned into a breeding area by a large tide. In November, when the combination of a large tide and heavy rains created over 220 hectares of mosquito breeding, the entire area was treated over a two day period. There was a substantial reduction, from an average of 271 Ae vigilax /trap night in Darwin's northern suburbs in the last three months of 1985, to 8 /trap night for the same time in 1986. As well as being very effective this technique applies an insecticide which targets mosquito larvae specifically, thus leaving this fragile environment undamaged.

Other mosquito breeding areas around Darwin were regularly monitored and the Darwin City Council advised when control was required. The problems at particular sites such as Leanyer Dump, Casuarina Beach, Coconut Grove, Vesteys Beach and the Botanical Gardens have thus been mitigated by the judicious application of larvicides. Table 5 shows the numbers of selected species of mosquitoes collected at Casuarina, Coconut Grove and Leanyer Dump for the last 5 years.

As well as construction and maintenance of drains in Leanyer Swamp, the Mosquito Control Engineering group has co-ordinated the survey of Casuarina sand dunes and commenced the rectification of the drainage problems there. Other mosquito trouble spots have been located and rectified throughout the year. Thus mosquito problems associated with the Tiger Brennan Drive extensions were alleviated by improved drainage, earth drains were constructed at Kululuk and Leanyer, and concrete drains installed at Stuart Park.

The control of mosquitoes in other centres is being co-ordinated as part of the National Disease Control Program. Those towns taking part in the program were Alic~ Springs, Jabiru and Darwin.

While the Nhulunbuy Corporation receives no assistance, their mosquito control program is conducted with liaison and monitoring assistance from the Department. Investigations by the Branch in Alice Springs during the year highlighted existing vector control problems and assisted in an indepth environmental report, which should lead to the rectification of the high mosquito numbers in Il Parpa Swamp. Visits to Jabiru highlighted operational problems with the fogging operations and recommendations were made for increasing the effectiveness of the program.

Public Awareness Program

"Make a mozzie mizzrable" was the slogan for this years mosquito awareness campaign, and the artwork depicting a mosquito and the s 1 o g an re c e i v e d w i de me di a cove rage . '·· The s t i c k e r , e ye - c at c hi n g singlets, a computer program, microscope display and a mossie competition were used to focus attention on public displays. All regions co-operated in the exhibition of material provided by the Branch and co-ordinated by the Health Promotion Unit. Television advertisements featured potential backyard mosquito breeding places, and the advertisement for personal protection has been timed to coincide with the camping season. A great deal of interest was shown in the displays mounted in the shopping centres and at the Rural Show. This was typified by the success rf the mossie competition which involved guessing the number of mosquitoes in a jar, which attracted over a thousand entries. An entomological investigation conducted pre- and post- campaign showed reduced numbers of mosquitoes when compared with last year, but that there was s t i l l considerable backyard breeding.

This is particularly worrying with regard to Aedes aegypti, which could easily become established in Darwin i f re-introduced.

Talks were also given to nurses and other malaria and insects of medical importance.

Co-operative Research and Liason

health workers on

The Branch again assisted with the National Vector Control Course at Mildura, Victoria. Three WHO Fellows from the Solomon Islands visited the Branch in November for training in exotic insect surveillance and vector control, and students from the Horticulture section of the Darwin Institute of Technology were also advised on aspects of insect control.

Seminars were presented at the C. S. I. R. 0. seminar series in Darwin, and the National Disease Control Working Party Meeting in Canberra.

Co-operative research was undertaken with a number of organizations and included host preference studies, electrophoresis identification trials and assistance with a cuticle hydrocarbon study of malari~ vectors with the School of Public Health and Tropical Medicine. An enhanced picture of arbovirus transmission in the Territory is being obtained through work on virus isolations from mosquitoes from various sources in conjunction with the Department of Primary Production. Assistance was provided to the Menzies Institute in their work on detecting vectors of Trachoma.

Liaison with other departments included representing the Department on the Coastal Management Technical Advisory Group and the Mosquito Control Engineering Group. Ongoing liaison with the Department of Lands and the Conservation Commission focused on numerous planning and environmental matters related to developments and potential mosquito breeding.

Publications

Whelan, P. I and Booth, D. R.

Mosquito Breeding at Il Parpa Swamp, Alice Springs Kelton, W. K.

Batchelor Mosquito Survey - June 1987 Davis, G. P. and Kelton, W. K.

Vector Mosquito Survey - Katherine, Apri 1 1 986 Davis, G. P. and Smith, E. S. C.

Vector Mosquito Survey - Gapuwiyak, May 1985 Davis, G. P. and Kelton, W. K.

Vector Mosquito Survey - Maningrida, April 1984 Whelan, P. I. and Weir, T. I.

Skin Lesions caused by Paederus australis Guerin - Meneville

< Coleoptera: Staphylinidae) . J. Aust. ent. Soc. ( in press)

Peter Whelan

Senior Medical Entomologist Medical Entomology Branch DEPARTMENT OF HEALTH

AND COMMUNITY SERVICES

TABLE 1 Aedes aegypti SURVEILLANCE PROGRAM

DARWIN CITY AND SUBURBS * JULY 1986 TO JUNE 1987

MEDICAL ENTOMOLOGY BRANCH - DEPARTMENT OF HEALTH AND COMMUNITY SERVICES

1986 1987 TOTAL

MONTH JUL AUG SEP OCT NOV DEC JAN FEB MAR APR JUN JUL

Ovi-traps sampled 42 41 39 43 40 44 42 44 44 44 20 42 485

Ovi-traps positive 25 29 25 23 27 30 35 34 33 37 15 34 347

SPECIES AND NUMBER OF TIMES RECORD~D

Ae.notoscriptus 25 29 25 23 27 30 33 34 33 36 15 33 343

Ae.tremulus 0

0

1 1 2 2 7 2

0

3 1 1 20

Cx.quinquefasciatus 0 0 0 1 2

0 0 2

1

0

0

2

8

Cx.pullus

0 0

0 0 0

0

0

0

0 1 0 0 1

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TABLE 2 EPIDEMIC POLYARTHRITIS CASES IN THE NORTHERN TERRITORY, 1986-87 Based on data from contributing laboratories

Hedi cal Entomology Branch, Department of Health and Community Services

Date of Place of Age Probable Antibody IGH

first residence and point of titre detected

blood sex infection

sample

28/7/86 Jabiru 30, F Jabiru 1!640 yes

29/12/86 l<ather i ne 25, F Katherine 1:20,1:160 yes

3/1/87 Katherine 33, F Katherine 1:80 yes

5/1/87 Katherine 31, M Katherine 1:300 yes

9/1/87 Darwin 55, F Hataranka 1:160 yes

13/1/87 Darwin 35, F Mataranka 1:320 yes

16/1/87 Katherine 42, F Katherine 1!160 yes

19/2/87 Katherine 19, H Roper Valley 1:20,1:160 yes 24/2/87 Katherine 24, F Borroloola 1!640,1!320 yes

26/2/87 Borroloola 36, M Borroloola 1!40 yes

16/3/87 Borroloola 31, F Borroloola 1!320 yes

16/3/87 Darwin 37, H Darwin 1:320 yes

19/3/87 Palmerston 34, H Nhulunbuy 1!320,1!640 yes

21/3/87 Darwin 45, H Darwin 1!160 yes

21/4/87 Adelaide River 37, F Adelaide River 1!80 yes

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^19/5/87 Groote Eylandt 27, H Groote Eylandt 1!160 yes

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TABLE 3. MOSQUITOES COLLECTED FOR VIRUS ISOLATION - JULY 1986 TO JUNE 1987 MEDICAL ENTOMOLOGY BRANCH - DEPARTMENT OF HEALTH ANO COMMUNITY SERVICES

SPECIES

An.amictus An. annulipes An .ban croft ii An.farauti An.hill i

An.meraukensis An.novaguinensis Ae. lineatopennis Ae.normanensis Ae.notosciptus Ae.phaecasiatus Ae.vigilax Ae.funereus Ae.reesi

Cx.annulirostris Cx.bitaeniorhynchus Cx.pul lus

Cq.xanthogaster Ha.uniformis TOTALS

DARWIN NO. NO.

HOSQ. +VE

8

63 50 37 139 105 18 724 116 878 28 7072 149

105 9492

1

1

2

HATARANKA NO. NO.

HOSQ. +VE 398

396

674 13324 1 29

24 5 7 35

PEPPIHENARTI 8. PALUHPA NO. NO.

HOSQ. +VE 453

27 308 23 41

151 3732

15043 1

16 383

4983 0

As at 16.7.87 only a few collections from Darwin and Hataranka examined by Virology Laboratory

TOTALS - ALL CENTRES NO. NO.

HOSQ. +VE 851

431 308 86 50 78 139 779 13342 753 140 883 7 63 10955 149 16 383 105 29518

0 0 0 0 0 0 0

0 1 1 0 0 0 0

1 0 0

0 0 3

. 'Tab.le 4.

~ MosQuito Monitoring Darwih Leanyer Dump 1984. 1985

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1986

1984

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TABLE 5 MOSQUITO MONITORING PROGRAM - DARWIN, 1983 TO 1987 HALF-YEARLY COLLECTIONS OF SELECTED SPECIES JANUARY TO JUNE

Total number of female mosquitoes collected in weekly CO2 traps

MEDICAL ENTOMOLOGY BRANCH DEPARTMENT OF HEALTH AND COMMUNITY SERVICES TRAP

LOCATION

Casuarina

YEAR SPECIES COLLECTED

An. farauti An. meraukensis Cq. xanthogaster I An. bancrofti i Ae. vi gi lax I Ma. uni for mis I I An. hi l l i I Cx. annulirostris

1983 401 1984 650 1985 752 1986 310 1987 305

1287 21 306 4

1 02 9

90 9

163 7

164 62 30 29 34

1431 1266 336 188 641 245 849 896 649 1078 1246 99 502 1106 50

11 4 78 1 3 8

46

Coconut Grove 1983 1403 2365 75 1984 1933 1056 2

1324 738 10989 464 221 64 6438 609

75 150 40 32 48

Leanyer Dump

1985 563 335 14

1986 128 236 13

1987 78 84 51

1983 336 1984 779 1985 174 1986 120 1987 80

2284 317 2043 69 105

274 644

257 38 83

120 408 3476 498 27 2812 2623 163 78 90 1295 47

688 369 91 53 93

518 43 134 258 1 81

5817 227 132 4068 1435 93 6310 402

4053 181 4565 102

170 96 356

TOTALS

5020 2174 3300 2869 2213

17433 10473 5454 6034 1771

10319 8899 7643 5073 6104