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| Journal of the New Zealand Medical Association,
08-September-2006, Vol 119 No 1241
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Erucism in New Zealand: exposure to gum leaf skeletoniser
(Uraba lugens) caterpillars in the
differential diagnosis of contact dermatitis in the Auckland region
José Derraik
Introduction, biological notes, and distribution‘Erucism’ is the term generally used to refer to
the adverse reactions resulting from contact with urticating caterpillars, the
larval forms of the insect order Lepidoptera (moths and butterflies).1,2
Although erucism is a relatively common public health problem throughout the
world,1 there are no indigenous species of Lepidoptera in New Zealand whose
caterpillar is known to cause adverse reactions in humans (Brian Patrick, Otago
Museum, personal communication; 2006).3 As a result, erucism has never been a
human health issue in this country, and is therefore a condition somewhat
unknown to local medical practitioners.
The situation has changed however, since the establishment
of the gum leaf skeletoniser Uraba lugens
Walker (Lepidoptera: Nolidae), an Australian moth whose caterpillar feeds
on the foliage of gum trees
(Eucalyptus) and other closely related
genera.4 The younger larvae avoid feeding on the oil glands and veins found in
the leaves, which are consequently ‘skeletonised’.3 More mature
larvae will however eat the whole leaf.3
Uraba lugens is a
significant pest for Eucalyptus
forestry. Infestation by U. lugens
may kill young trees if there is repeated defoliation.5 This process on
larger trees may reduce wood production for several seasons.6 Outbreaks of this
species seem to periodically occur in natural forests in Australia, but these
eventually recover, even though defoliation can be severe.7
Uraba lugens was
first discovered in New Zealand in 1992, and it is now firmly established in the
Auckland region, over an area of at least 20,000 ha.4 Due to its wide
distribution, eradication was deemed to be not feasible.8
Uraba lugens is now the focus of a
long-term management programme aiming particularly at filling current knowledge
gaps and controlling the existing population.8
The approximate distribution of
U. lugens currently goes as far north
as Takapuna and as far south as the Bombay Hills, including the area between the
Hunua Ranges in the east and the Manukau Heads and Waitakere Ranges in the
west.7 The highest density of this organism seems to occur in southwest
Auckland.9 Results from climatic models indicated that
U. lugens could potentially establish
throughout New Zealand. To date, the population is not known to be established
outside the Auckland region, but specimens have recently been captured in
pheromone traps in Katikati (Bay of Plenty) and Warkworth (Northland).18
The Auckland populations of
U. lugens have two generations per year
(bivoltine), with larvae usually present from January to March (summer) and May
to October (winter).10 Uraba lugens
caterpillars vary in length from 1 to 25 mm depending on the stage of
development.3. There are between 11 and 13 larval stages.4,5
Uraba lugens are
extremely hairy caterpillars with yellow and brown markings, and when mature
they retain the head capsules of previous instars that are pushed up to top of
the head, which makes U. lugens easy to
identify (Figure 1).5 Each body segment of the larvae has 10 tubercles, four of
which are located dorsally and have short, stiff, brown-tipped bristles that are
hollow and contain venom that can be injected into the human skin upon
contact.3
Figure 1. Uraba
lugens caterpillars (Photo courtesy of Ensis)
 Exposure, symptoms of envenomation, and possible treatmentThe exposure of people to stinging caterpillars is greater
when these creatures are occurring at high densities, as numerous caterpillars
may be found in the direct vicinity of an infested tree. Large infestations of
stinging caterpillars can become a serious public health issue, and in some
severe cases it has led to the closure of schools.2
Figure 2. Wheals formed approximately 30 minutes after
exposure to the urticating spines of Uraba
lugens (Photo courtesy of Ensis)
 Most cases of harmful exposure to caterpillars seem to occur
in young children, and in one study of 365 cases of exposure to
Lophocampa caryae Harris (Lepidoptera:
Arctiidae), 80% of the records were paediatric exposures.11 Caterpillars are a
source of curiosity to children due to their easy accessibility and slow
mobility,11 and also due to these creatures’ generally bright colours.
Young children tend to have thinner skin and smaller bodies than adults, both of
which may increase the extent of the reaction.12
Approximately 150 species of Lepidoptera from more than a
dozen families have been described to cause some form of injury to humans.1,13
The caterpillars of many species have chitinous spines that are capable of
penetrating human epidermis, and injecting venom parenterally.13 Exposure to
stinging caterpillars can result in a variety of reactions, which vary according
to the species,14 but adverse reactions range from moderate to severe local
effects, usually characterised by severe pain, and less commonly systemic
effects,14 including renal failure and intracerebral hemorrhage.1
The nature of U. lugens
venom is largely unknown,12 but it contains histamine and most likely
also a proteinaceous substance.3 Skin contact with the envenomating bristles of
U. lugens will immediately cause a
sharp stinging sensation, which may be severe.3 Local pain is followed by the
associated formation of flat itching wheals (Figure 2),15 which may remain
visible for a few weeks.3
The skin reaction may cause a high degree of discomfort, and
an adult woman described the reaction as “violent and distressful for
3–4 days”.3 As a result, adverse reactions to
U. lugens venom may be particularly
distressing for young children. It is important to note that even the spines on
the youngest caterpillars are capable of stinging, and that these continue to
sting even after the insect is dead, and also following the shedding of
skin.3
Ingestion of caterpillars of other species by children has
been described in the literature,1,14,16 with some adverse effects consisting of
pain, difficulty swallowing, drooling, and shortness of breath.16 There seem to
be no records of U. lugens ingestion,
but it would be likely to require hospitalisation. While life-threatening
reactions are unlikely to occur, the possibility of serious adverse reactions,
such as anaphylaxis, cannot be discarded.12 Although severe and systemic
reactions to U. lugens have not
been described, eye lesions could be potentially serious and should be dealt
with by a specialist. Note that there is no evidence of sensitisation from
repeated exposures to U. lugens.3
Contact with some caterpillar species such as the
white-stemmed gum moth (Chelepteryx
collesi) leads to a very large number of hairs becoming embedded in the
skin.17 Even though for some species attempts to remove the hairs seem to be
unsuccessful,17 the careful removal of spine(s) with adhesive tape is a commonly
prescribed initial treatment of urticating caterpillar stings.2,14 However, this
is not likely to be an issue with U.
lugens, as there seem to be no reports of its spines becoming embedded in
human skin, especially in Southcotts’s detailed descriptions of numerous
cases of exposure.3 Instead, the application of ice packs, and oral or topical
administration of antihistamines to attenuate itching and burning sensation, is
advised.1,2,14 Intense inflammatory reaction may be locally relieved by topical
or oral corticosteroids.1,2
Current incidence and recommendationsThere are no available data on the incidence of exposure to
U. lugens in New Zealand. Biosecurity
New Zealand has information on at least two confirmed cases, where members of
the public have contacted the agency following adverse reactions to an
‘unknown’ caterpillar (Mark Ross, personal communication; 2006).
However, based on the distribution of the caterpillars in the Auckland region
and its relatively high density in some areas, one could expect the actual
number of cases to be considerably higher. The author would welcome information
on any confirmed cases of exposure to U.
lugens in New Zealand.
Even though U. lugens
is the target of a long-term management programme, this species is
well-established in the Auckland region and will not be eradicated. Since
Auckland is the most populated region in the country, human exposure to the
caterpillars is likely to occur on a regular basis, particularly among children.
As a result, general practitioners should consider exposure to
U. lugens in the differential diagnosis
of contact dermatitis, where symptoms such as wheals are present.
Prevention is an important tool, and in cases where exposure
to U. lugens is confirmed, the access
of children to areas adjacent to infested trees should be restricted, and a
reputable pest controller should be contacted for mitigating action. In case the
infested tree is located on public land, the local or regional authority should
be notified.
Avoidance is a fundamental preventive tool, and children
should be educated not to touch or handle U.
lugens caterpillars. It should be also noted that this species’
potential establishment in Eucalyptus
plantations in New Zealand may lead to occupational safety and health concerns,
as a result of the likelihood of exposure to forestry workers.12
Author information:
José G B Derraik, Advisor (Human Health), Risk Analysis Group,
Pre-Clearance Directorate, Biosecurity New Zealand, Wellington
Acknowledgements: I
thank John Fountain (National Poisons Centre, University of Otago), Doug Lush
(Ministry of Health), and Ian Gear and Mark Ross (Biosecurity New Zealand) for
revising this manuscript and providing valuable feedback. Ensis Forest
Biosecurity & Protection has kindly allowed their photographs to be included
in this article. Thanks also to Brian Patrick (Otago Museum) for input.
Correspondence:
José G B Derraik, Biosecurity New Zealand, PO Box 2526, Wellington. Fax:
(04) 894 0733; email: jose.derraik@maf.govt.nz
References:
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