insect_bites

insect bites and stings in Australia

introduction

  • biting and stinging insects of medical concern in Australia include:
    • Diptera - mosquitoes, flies and gnats
    • Hymenoptera - ants, bees and wasps
    • Phthiraptera - lice
    • Siphonaptera - fleas
    • Hemiptera - bugs including bed bugs

mosquitoes (Culicidae)

introduction

  • mosquitoes are a common problem in Australia with over 300 species, but fortunately Australia is not a malarial country (it was endemic in the tropics but was eradicated in 1981) and only a few species are a concern for disease transmission
  • the main diseases carried by mosquitoes in Australia are:
    • dengue fever in the tropical north Queensland (eg. Cairns region) at certain times of the year, spread by Aedes aegypti
    • Murray Valley encephalitis virus - north-western Victoria and other states, particularly after floods (eg. La Nina years such as 1951, 1974, 2011) as host is water birds. High subclinical rate with only 1 in 500 becoming ill.
    • Kunjin encephalitis virus - rare infections - perhaps 1 a year.
    • Ross River virus - epidemic polyarthritis, occurs in all states of Australia and is the most common mosquito transmitted disease with over 6,500 cases per year with occasional local epidemics with much higher numbers.
    • Barmah Forest virus - epidemic polyarthritis; found near Echuca on the Murray River as well as other States, but prevalence is 1/10th that of Ross River infections.
  • the most common problem is hypersensitivity reactions (often delayed onset) to the bites although fortunately, anaphylaxis is rare.

other flies

introduction

the common house fly

  • is a household nuisance introduced by the British on the early convict ships
  • it prefers to live inside houses and breeds in, and frequents nearby locations (usually within 50m of the house) which tend to be well populated with potentially pathogenic bacteria which the fly can vomit up (this helps dissolve dried substances) or leave excrement on human skin or on objects we touch or, on our food.
  • they breed in rotten vegetation or carcasses, including lawn clipping mulch > 2cm deep, compost, rubbish bins, or in sewage.
  • each fly carries several million bacteria!
  • they have the potential to spread amoebic dysentery, anthrax, cholera, gastroenteritis, parasitic worms, paratyphoid, poliomyelitis, salmonella, shigellosis, trachoma, tuberculosis, typhoid fever, typhus, but fortunately these are quite rare in Australia, and food contamination issues are minimal if proper food handling is maintained.
  • they taste with their sticky feet and thus tend to spread bacteria by walking over everything.
  • they do not bite

the Australian bush fly

  • these are the flies that are really annoying at those Summer barbecues or bushwalks.
  • they have become out of control following the introduction of cattle to Australia.
  • they only breed in animal dung, and cattle dung is much bigger and more moist than native Australian animal dung and makes a perfect breeding ground (as long as they are not swamped with rain or flood water). This is particularly so in Australia as there are no native cattle dung beetles to control them (native dung beetles tend to be most abundant in Winter), and introduced dung beetles tend to be most abundant in Summer - too late to control the Spring burst of bush fly breeding.
  • these breed by their millions in Spring (once maximum daily temps exceed 18degC) across the cattle farms in inner Australia where the Winter is warmer, and then strong winds on warm days blow them to urban areas - thus:
    • hot westerly winds blow them into Sydney Nov-Jan with peak numbers occurring in January
    • hot northerly winds blow them south to Canberra, Melbourne and Perth, usually with numbers increasing significantly after mid-Nov and peaking in December and lasting until end of January, although some will be present until April in eastern states.
    • the winds take them over the sea, and occasionally, they can be a problem in Tasmania.
    • Brisbane does not tend to get significant numbers as summer is too wet for them to breed locally and only a few blow in with the westerly winds.
    • they are common most of the year in the northern subtropics but numbers fall during Spring, and start to build up with Summer rains to peak in Autumn.
    • in drier north-west tropics, the build up is in late Autumn, with a rapid decline in Spring and almost none in the summer 'wet'.
    • although numbers are low in desert areas, they are poorly nourished and thus small and annoying most of the year, and the presence of a human will be like a light to a moth!
  • bush flies only fly at temperatures above 12degC and fly the most at 27degC. They prefer the sun and avoid indoors or shady areas such as forests unless temperatures exceed 35degC.
  • the females are the main ones attracted to humans as they need protein for ovarian function, and thus they like to get to tears, saliva and blood (from open wounds). The smaller ones need the most protein and tend to be the most annoying. Males may annoy humans when they are thirsty.
  • they seem to prefer light colours, particularly yellow (whereas house flies prefer red, black, and March flies prefer dark blue)
  • they do not bite, do not lay maggots in tissue (only in dung) and rarely transmit disease, although there is a risk of trachoma transmission.
  • hopefully the bush fly issue will come under control with the introduction of new dung beetle species.

the blow fly

  • these appear to have come to Australia from Africa in the 1880's and had become a serious pest in eastern Australia by 1915, and Western Australia by 1930's, and became a problem in Tasmania by 1957.
  • these flies are larger and lay maggots in carcasses, and even on live animals - particularly sheep which is a major problem for farmers, particularly now that these flies have become resistant to chemical sprays.
  • they are generally not an issue with humans, but have been known to cause maggot infestations in neglected wounds such as decubitus ulcers in the frail elderly.
  • these maggots are the ones preferred by fishermen for bait.

the March fly (Tabanidae)

  • these are larger, stout bodied flies which have a painful bite and their saliva which prevents blood from clotting, may cause an allergic reaction.
  • they prefer moist ground, and thus tend to be found along streams in late Summer in particular.
  • they tend to be very persistent as they suck blood from the human skin and are attracted to dark colours, particularly blue in open sunlit fields
  • prevention may require wearing loose, light coloured clothing and use of a DEET-type lotion repellant.

the Stable fly

  • these are another biting fly which breeds in hay contaminated with urine and dung, hence their predilection for being around horse stables abd dairies.
  • they are a major problem in Perth
  • their preference is to bite and feed on the lower legs of cattle.
  • they look like house flies but have a needle like proboscis at their mouth.

biting midges (sand flies)

  • NB. these are different insects to the sand fly of north-western NSW and western Queensland!
  • sandflies are small 1-3mm robust jet black insects with piercing and sucking mouthparts that belong to the family of flies Ceratopogonidae.
  • they are so small they can get through standard insect screen meshes so use smaller meshes when camping and spray them with insecticides.
  • renowned for their nuisance biting associated with tidal sea-water habitats such as coastal lagoons, estuaries, mangrove swamps and tidal flats and prefer calmer waters.
  • they breed in wet sand and populations can grow rapidly in warm weather as females produce 30-50 eggs, however, adults only live for a couple of days (whole life cycle takes 3-10 weeks) and can range up to 500m from breeding ground (sometimes up to 5km up valleys if wind carries them)
  • tidal waters rising and falling against a vertical surface such as a seawall eliminate the midge problem for the length of foreshore so treated.
  • a major problem in northern Australian mangrove areas in particular but also can be problematic on most coastal areas, in Victoria, Gippsland tends to have more of a problem than the western districts
  • the biting activity of adult biting midges is mainly limited to the periods of dawn and dusk but may continue overnight and on cloudy days, and seem to be particularly active at low tide on beaches on warm nights with little breeze.
  • they will remain inactive through very windy weather, finding shelter amongst vegetation.
  • emergence of adults of some species relates to lunar cycles and numbers seem to be higher after spells of hot weather and at neap tides
  • Female midges may attack humans in large numbers, biting on any areas of exposed skin, and often on the face, scalp and hands. Some species will blood feed on a wide range of animal hosts.
  • bites often cause discomfort, and itching which may be delayed for 12-24 hours
  • local residents seem to build up some immunity to the biting.
  • in some sensitive people, midges can produce persistent reactions that blister and weep serum from the site of each bite and these reactions may last for several days to weeks.
  • not known to transmit disease although there appears to be potential for midges to transmit leishmaniasis 1)
  • lotion formulations of DEET are recommended repellents (but only last 2hrs and need to be re-applied) while fishermen mix zinc cream with various home remedies such as citronella oil, vinegar, etc to help repel them.
  • NB. another type of biting midge belonging to the genus Leptoconops appears in the sandstone gulleys of the Berowra-Bobbin l-lead area (just north of Sydney) each year about October and November. This species is typically a daytime head biter, especially inside the ears of animals and around the hairline on humans. lt also bites close to the eye and can cause “bung eye”, a gross but painless swelling of both lids with even complete closure of the eye

bees and wasps

  • most of these can sting, and some people may develop potentially fatal anaphylaxis
    • 1 in 30 people are allergic, a new vaccine may be available soon to prevent serious reactions
  • Australia has over 1,500 species of native bees and of course, the introduced European honey bee to which 1.6% of people are sensitive
  • Australian wasps are usually not an issue but the much more aggressive introduced European wasp (Vespula germanica) has become a significant issue as it often stings repeatedly and discharges pheromones to alert other wasps to join in. This wasp reached mainland Australia in Melbourne in 1977 and appears to be restricted to the cool and wet climates of coastal southern Australia.

caterpillars and moths

  • some moths (eg. Onchogaster lunifer) have barbed, hairy filaments (setae) that are known to cause urticarial rash, corneal inflammation, and facial oedema.
    • the moths envenomate humans after people come in contact with the irritant produced by a gland at the base of setae on their feet
    • rarely, this may result in osteomyelitis of the phalanges, presumably associated with retention of the setae in the skin of digits
  • processionary caterpillars have been associated with outbreaks of paediatric dermatitis, conjunctivitis and respiratory illness.

ants

  • Australia is almost the only place on earth that is home to the bull ant family of ants (Myrmecia sp. which evolved some 110 million years ago).
    • in the Southern states, bull ants are least active in Winter
    • Myrmecia stings are very potent, and the venoms from these ants are among the most toxic in the insect world.
    • many of these can deliver painful stings and some people are hypersensitive and are at risk of anaphylaxis, especially to Jack Jumper ants (M. pilosula sp.) to which 2.3% of humans are sensitive
    • these ants are capable of stinging through fabric such as cotton gardening gloves
  • in Australia, the green-head ant (Rhytidoponera metallica) is the only ant other than Myrmecia species to cause anaphylaxis in people
  • the introduced pest, the Argentine ant (Linepithema humile) is much smaller and dominates urban areas but does not inflict a painful bite
  • the Iridomyrmex alpinus is a small (~3mm long) aggressive ant found in alpine areas of south-eastern Australia and can be very annoying for bushwalkers camping on mountain peaks as they tend to swarm over bare limbs if they come in proximity to their nests often hidden in ground foliage although they do not sting and their bites are not much more than sharp nips
  • other Iridomyrmex sp are mainly found in rural areas (and are almost unique to Australia, having evolved some 12 million years ago) and also tend to swarm and bite, the largest of these are the I. purpureus species group, the “meat ants”

"sea lice"

insect_bites.txt · Last modified: 2019/07/17 04:19 by gary1