Mosquito borne disease in the Northern Territory

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Northern Territory Department of Health Library Services Historical Collection

DL HIST

614.4323

WHE

1988

OEPA.RTlilENT OF 1-4EA.LT~

AHO~TYSERVICES

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MOSQUITO BORNE DISEASE IN THE NORTHERN TERRITORY

For further information contact: Peter Whelan

Senior Medical Entomologist Medical Entomology Branch

Department of Health and Community Services P. 0. Box 1701 , Darwin

Telephone: 208 333

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- MOSQUITO BORNE DISEASE IN THE NORTHERN TERRITORY

46278

CENTRAL LIIRARY

- 6 MAR 1998

TERRITORY HEAL TH SERV1CES

The Northern Territory has a history of various mosquito borne diseases, including malaria, dengue, Australian encephalitis and epidemic polyarthritis. Malaria transmission has been eradicated from the Northern Territory, but each year we have a number of imported cases from overseas malarious countries that make us vulnerable to i t s reintroduction. The vector of dengue has not been established in the Northern Territory for many years, and although there are occasional instances of imported insects, we are not receptive to this disease. It is s t i l l probable to be infected in the Northern Territory with the causative viruses of the other two diseases mentioned above. The Medical Entomology Branch of the Department of Health and Community Services has ongoing programs of mosquito monitoring, control and awareness throughout the Northern Territory to reduce the incidence of these diseases.

MALARIA

Malaria is a parasitic human blood disease carried only by Anopheles mosquitoes. The last epidemic of malaria in the Northern Territory occurred in 1955-57, with 750 cases reported.

The last indigenous case was in 1962 at Roper River. However, the Northern Territory is receptive to malaria reintroduction.

There are a number of confirmed and suspected Anopheles vectors in the Northern Territory, and these mosquitoes can occur in particularly high numbers around towns and in tourist areas.

With the worldwide resurgence of malaria and the spread of drug resistance, the risk of malaria reintroduction to the Northern Territory is increasing. This risk is further increased with the rising numbers of people travelling between the Northern Territory and neighbouring malarious countries. There has been a

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large jump in the number of imported cases of malaria in the Northern Territory in the 1987-88 year, with 29 cases reported.

This compares with 18 cases in the 1985/86 year, and 19 cases in 1986/87. These cases were mainly imported into the Darwin area.

Two cases occurred in the Nhulunbuy area which is particularly vulnerable, with large mosquito breeding areas close to residential areas. The bulk of the cases were from Indonesia and Papua New Guinea and five were of the potentially fatal form of falciparum malaria (See Table 1). Five of the cases required fogging operations to reduce the risk of transmission.

DENGUE

Dengue fever is a mosquito borne virus disease carried primarily by the dengue fever mosquito. It causes fever, severe muscle and joint pains, and in some cases there is internal and external bleeding. Although the vector of dengue fever has not been established in the Northern Territory for many year~, the mosquito could be introduced at any time. This mosquito breeda in close association with human habitation, in rain filled containers such as tins, tyres, rainwater tanks and pot plant drip trays. The mosquito has been reported from Mornington Island in the Gulf of Carpentaria and could be introduced by sea or land traffic from Queensland. Illegal landings on our north coast also pose a risk for the reintroduction of this and other related species.

The Medical Entomology Branch conducts regular mosquito monitoring programs and surveillance operations to intercept and prevent possible introductions of this species. The prevention of the disease is dependent upon keeping the vector out of the Northern Territory. This can be achieved by reducing the available breeding sites in towns, as well as intercepting the mosquitoes at likely points of entry. If the mosquito can be kept out of the Northern Territory, we will not have this disease.

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AUSTRALIAN ENCEPHALITIS

Australian encephalitis is a potentially fatal infection with a mosquito borne virus, usually Murray Valley encephalitis virus

C MVE), al though i t has been reported rarely from Kunj in virus.

Australian encephalitis is regarded as endemic in northern Australia. There was an Australian wide epidemic in 1974, including five cases in the Northern Territory, but none occurred north of Katherine despite the greater concentration of people in the Top End. The only subsequent confirmed case of Australian encephalitis since 1974 has been one on Groote Eylandt. The MVE virus has not been isolated in the Top End of the Northern Territory since at least 1972, when the Medical Entomology Branch was established, despite extensive sampling.

However, there have been four recent cases of this disease in the Northern Territory <See Table 2).

male virus

infants in the months of July, has been implicated in all

The recent cases occurred in March, April and May. MVE four cases. The four cases, three Aboriginal and one Caucasian, occurred in small communities with relatively high numb~~s of the common banded mosquito. The present cases confirm that this disease is present in the Northern Territory in non-epidemic periods. The incidence of this disease may signify an increased awareness of arboviral diseases by medical personnel in the Northern Territory. It certainly emphasises a need for continued public education programs and for mosquito reduction programs, at least around the major population centres.

EPIDEMIC POLYARTHRITIS

Epidemic polyarthritis is a mosquito borne virus disease caused by Ross River virus. The symptoms include fever, rash and arthritis. It is rare in patients less than 15 or older than 60 years. There are a number of mosquito vectors involved in the spread of this disease. Ross River virus is a disease of animals and people. The major animal reservoirs in Australia are the larger marsupials. The disease is found throughout mainland Australia and Tasmania. In Australia there are occasional large outbreaks associated with summer rainfall and flooding. The most

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cases reported each year are from Queensland. In 1986 there were approximately 600 cases reported from Queensland, with 200 from

.

Victoria, 40 from New South Wales, 70 from South Australia and 13 from the Northern Territory.

There have been a lot of media reports on a "outbreak" of epidemic polyarthritis in the Jabiru area this year. As can be seen from Table 3, there has been an increase in the number of cases in the Darwin region, from 8 in 1987 to 21 in 1988.

However, the total cases in the Northern Territory this year represents only four more than last year.

reported from the Jabiru area (See Table

Ten of the cases were 4), but this could be due to an increased awareness of the disease as well as a real increase in the incidence of the disease.

The main vector species in the Darwin region are both the common banded mosquito and the salt marsh mosquito. The common banded mosquito is of more importance in the Jabiru area (See Table 5> . Most of the cases in the Northern Territory have occurred in the December-April period, with the highest number of cases occurrin~ in February (See Table 5). Local Councils in the major towns, in liason with the Medical Entomology Branch, have ongoing mosquitQ monitoring and control programs, to reduce the potential for disease transmission within the towns. However, for small communities and other areas, self protection must be the mainstay in the prevention of this disease.

measures such as mosquito proof houses

Simple self or tents,

protection protective clothing, mosquito avoidance and repellents will generally be sufficient to prevent infection. The Department conducts regular public awareness programs and distributes

the general public on these aspects.

MOSQUITO CONTROL

information to alert

The Department of Health and Community Services has assumed responsibility for totally funding the Northern Territory portion of the

Under

former Commonwealth National Diseases Control Program.

this program the Medical Entomology Branch maintains mosquito monitoring and surveillance programs throughout the Northern Territory. Technical and funding assistance is given to

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local Councils of the major towns to help run mosquito control programs.

In the Darwin area, a separate and extensive mosquito engineering control program has largely brought the extensive coastal mosquito breeding sites under control. Large areas of salt marsh mosquito breeding that cannot be drained are treated with a helicopter applied application of a new bacterial insecticide.

When investigations indicate that there is a danger of malaria transmission, or when the transmission of Australian encephalitis is likely to occur, the Department may carry out adult mosquito control. The insecticide of choice for these operations is a pyrethroid insectide (related to pyrethrum) which has been approved as a household space spray and has been used for spraying the cabins of international planes. The fogging is generally aimed at mosquito breeding and harbouring areas away from residential areas. However, when parasite or virus infected mosquitoes are present in residential areas, the fogging may need to include residential areas.

The Department of Health and Community Services has one of the best organised mosquito monitoring and mosquito control programs in Australia. The continued absence of Aedes aegypti and the lack of any malaria transmission can be largely attributable to these programs.

Peter Whelan

SENIOR MEDICAL ENTOMOLOGIST

August, 1988

Table 1. IMPORTED MALARIA CASES

IN THE NORTHERN TERRITORY, 1987 /1988

Location No. Country of Origin Species No.

of Cases Indonesia P. vivax Requiring

Cases P. N. G. P. falciQarum Mosquito

Africa P. malariae Control Other

Darwin 1 6 6 5 2 3 1 2 4 4+

Palmerston 3 3 3

Howard Springs

Batchelor* 1

Nhulunbuy 2 2 2

Katherine 3 3 2

Tennant 2 2

Creek Alice Springs*

Total 29 10 1 2 2 5 23 5 7+

*cases passed through Darwin

+includes response to cases in Alice Springs and Batchelor which passed through Darwin

TABLE 2.

AUSTRALIAN ENCEPHALITIS CASES IN THE NORTHERN TERRITORY, 1987/88

LOCATION

Belyuen

Maningrida

South Alligator

Haningrida

DATE OF ONSET

1/7/87

21/3/88

21/4/88

8/5/88

AGE RACE

1. 4 Aboriginal

0. 1 Aboriginal

0. 6 Caucasian

3. 75 Aboriginal

SYHPTOHS

Fitting,

fever, seizures, ataxia.

Fever, epilepsy hand tremor facial palsy

Fever, neck stiffness, epileptic seizures facial palsy

Convulsions

VIRUS IDENTITY

MVE

MVE

MVE

MVE

TABLE 3.

EPIDEMIC POLYARTHRITIS CASES IN THE NORTHERN TERRITORY 1980-88 MEDICAL ENTOMOLOGY BRANCH

N. T. DEPARTMENT OF HEALTH AND COMMUNITY SERVICES

Probable infection points for serologically confirmed cases of of epidemic polyarthritis cases submitted to the Pathology Laboratories, Darwin, based on first blood sample date.

REGION 80

DARRIN 7

KATHERINE BARKLY

ALICE SPRINGS 1?

EAST ARNHEM UNKNOWN OUTSIDE NT

TOTAL

*

As at 3/8/88

4

1 4

81 82

7 4

6

4

9 1 4

83 84 85 86

8 8 7 9

6 1 3 2 4

4

1 9 25 1 0 1 3

Note: Regions are as defined by Department of Health and Community Services with Darwin Region including Jabiru.

87 8 1 5

2

25

88*

21

4

2

29

Table 4.

Date of first blood

11/12/87 14/12/87 14/12/87 16/12/87 17/12/87 22/12/87 22/12/87 23/12/87 30/12/87 30/12/87 Dec. 87 4/1/88 5/1/88 5/1/88 6/1/88 7/1/88 18/1/88 20/1/88 25/1/88 27/1/88 28/1/88 29/1/88 29/1/88 1/2/88 12/2/88 15/2/88 15/2/88 17/2/88 18/2/88 22/2/88 24/2/88 24/2/88 26/2/88 29/2/88 7/3/88 14/3/88 14/3/88 29/3/88 16/4/88 28/4/88

EPIDEMIC POLYARTHRITIS CASES IN THEN. T., 1987-88 Based on data from contributing laboratories and assisting medical practicioners.

Place of Residence

Katherine Katherine Katherine Katherine Lake Bennett Darwin

Katherine Darwin Katherine Batchelor

Groote Eylandt Darwin

Numbulwar Lake Bennett Darwin

Katherine Katherine

Age and Sex

36,F 30,F 20,F 30,F 20,F 20,M 52,F 27,M 28,F 33,F 29, M 42,F 32,M 26,F 30, F 1 3, M 30,M

Darwin 7,F

Darwin 39,F

S' th Alligator 27, M

Darwin 30,M

Katherine 34,F Elliott 31, M

Darwin 42,F

Jabiru 31,F

Darwin 44, M

Jabiru 26,F

Jabiru 40,M

Darwin 28,M

Jabiru 27,M

Berry Springs 35, F Jabiru East 18,F

Darwin 49,F

Jabiru 37,F

Jabiru 26,F

Darwin 23,F

Jabiru 60,M

Groote Eylandt 27,M

Jabiru 30,F

Alice Springs 15, M

Probable point of Infection

Katherine Katherine Katherine Katherine Lake Bennett Noonamah Katherine Darwin Katherine Mary River Kakadu Darwin Numbulwar Lake Bennett Mary River Katherine Katherine Darwin N. T. /W. A.

Jabiru Darwin

Kath/Numbul.

Dunmarra Darwin Jabiru Darwin Jabiru Jabiru Darwin Jabiru

Antibody Titre

IGM

detected

Yes Yes Yes 1:40,1:160 Yes 1:320 Yes Yes Yes 1: 1 60

1: 1 60 1: 80 ·

Yes Yes Yes Yes 1: 1 60, 1: 1 60 Yes Yes 1:160 Yes 1: 1 60 Yes 1:20,1:640 Yes 1:160 Yes 1: 160

Yes Yes Yes 1:160 Yes 1: 40 Yes 1:80,1:20 Yes

1: 1280

Yes Yes Yes Yes 1:160,1:200 Yes 1: 80 Yes Yes Berry Springs 1: 160 Yes

Jabiru East Yes

Darwin Jabiru

1: 160 Yes Yes

Jabiru Yes

Darwin Yes

Jabiru Yes

Groote Eylandt 1: 160 Yes Jabiru 1: 160 Yes Alice Springs 1: 10, 1: 80

TABLE 5.

EPIDEMIC POLYARTHRITIS CASES IN THE NORTHERN TERRITORY 1980-88 MEDICAL ENTOMOLOGY BRANCH

N. T. DEPARTMENT OF HEAL TH AND COMMUNITY SERVICES

Seasonal prevalence of epidemic polyarthritis infection in the Northern Territory. The time of infection has been calculated as

14 days before date of 1st blood sample, 10 days before 1st symptoms or recollection of exposure to high numbers of mosquitoes. This data has been collected from contributing laboratories and Doctors from 1980-88.

Lines indicate probable vectors. Broken lines are used where identity of vector is particularly uncertain.

REGION DARRIN

Cx. ann Ae. vig EAST ARNHEM

KATHERINE

BARKL Y

ex.

ann Ae. Vig

ex.

ann Ae. nor

Ae. nor ALICE SPRINGS

Cx. ann

TOTAL

As at 7/7/88

J F H A H J J

8 34 10 6 4

2 2 2 2

9 . 1 5 5 3

1 ?

21 51 16 12 3 6

A s

3

4 0

ex.

ann = Culex annulirostris (common banded mosquito) Ae. nor - Aedes normanensis (floodwater mosquito) Ae. vig = Aedes vigilax (salt marsh mosquito)

0 N D TOTAL

2 1 0

3

3 1 6

3 5 29

79

1 6

53

2?

1 51

..