Science for Saving Species - Research findings factsheet Project 2.3.5
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Science for Saving Species
Research findings factsheet
Project 2.3.5
Understanding and treating a new Enterococcus bacterial
infection affecting Christmas Island lizards
In brief
A deadly infection caused by a Conservation managers lizards and that the incubation
new and unusual bacterium was quarantined affected animals from period is long. We trialled several
first observed in captive Critically the main population; however, antibiotics to determine if any would
Endangered and Extinct in the Wild they were not able to treat the have an impact and be a potential
Lister’s geckos (Lepidodactylus affected lizards, as it was unknown means of treatment.
listeri) on Christmas Island in late which, if any, treatments would
be effective. To fill this knowledge The findings will be of use to
2014. The infection was then
gap, we undertook carefully Christmas Island National Park and
identified in another captive
Critically Endangered and Extinct controlled experimental infection captive breeding staff as well as
in the Wild lizard species on and treatment trials to discover quarantine/biosecurity officers and
Christmas Island, the blue-tailed how the disease is transmitted, wildlife disease and conservation
skink (Cryptoblepharus egeriae), what the incubation period is and scientists. Their application has the
as well as in two species of invasive the effectiveness of five different potential to reduce the threat, and
gecko, the Asian house gecko antibiotic treatments. possibly the spread of this deadly
(Hemidactylus frenatus) and mute We found that infection likely disease to the captive populations
gecko (Gehyra mutilata), across happens due to bite wounds or of Critically Endangered Christmas
much of the east of the island. other direct contact from infected Island reptiles.
Background
The Australian external territory of have had the most significant impact 2014, following an outbreak in the
Christmas Island, 1550 km off the on native reptiles. captive Lister’s gecko population,
north-western coast of mainland which is likely to have resulted from
Around 10 years ago, out of concern
Australia, has reptile fauna that are direct contact with free-ranging
for their dwindling populations, Parks
found nowhere else. Although once invasive Asian house geckos
Australia established captive breeding
common on the island, some of and mute geckos.
programs for the blue-tailed skink
these species have become Extinct Since 2014, there have been a
and Lister’s gecko, which are now
or Critically Endangered following number of outbreaks within the
both Extinct in the Wild.
the introduction of invasive species captive blue-tailed skink population
since settlement. In particular, These captive breeding programs that are housed in large open-
the Asian wolf snake (Lycodon have become threatened by a aired pens called exclosures.
capucinus) and giant centipede recently emerged Enterococcus These outbreaks have resulted in
(Scolopendra subspinipes), which species of bacteria, known as the death of an unknown number
were introduced to Christmas Island Enterococcus lacertideformus. of animals and have been managed
via international ships are likely to We identified the disease in October by isolating affected animals.
Background (continued)
The disease causes visible facial We also discovered that the In order to better understand
deformation, with more advanced organism is genetically distinct; the on-going risk of infection
infection impacting bones, organs that is, it represents a novel species we have also investigated where
and tissues throughout the body. of Enterococcus bacteria. Because the disease was occurring on the
The progression of the disease it is a unique bacterial species island and how widespread it was.
varies widely among individuals that we were not able to culture Island-wide surveys demonstrated
and between species, but is for antibiotic sensitivity tests, we that this bacterial disease continues
ultimately fatal in geckos. had to experimentally infect and to occur in both species of invasive
treat lizards to determine effective geckos at multiple locations across
Treatment was not considered
treatment protocols. We used the island, indicating that future
an option at that time, as it was
highly invasive Asian house outbreaks are likely.
unknown which, if any, antibiotics
geckos collected in the wild on
would be effective. Given that
Christmas Island for these trials.
untreated infections result in the
animals’ certain death, conservation
Asian house gecko receiving an oral swab to confirm absence of E. lacertideformus
managers wanted to understand disease and enlistment into the experimental trial. Image: Jessica Agius
the pathology of the disease,
and whether antibiotics present
an effective option to treat
infected individuals.
Following the initial outbreak in
late 2014, we analysed the form,
structure and genetic make-
up of the bacterium to gain an
understanding of the causes and
effects of the disease. We found
that the bacteria is contained within
a kind of capsule that likely protects
it from the immune response of
the host and from some antibiotics.
Research aims What we did
The aims of the experimental The infection trial • Oral cavity (where we
infection and treatment trial The first step was to identify specific administered bacteria by mouth)
were to: infection pathways in invasive • Abdomen (where we injected
1. Identify the infection pathway free-ranging geckos on Christmas bacteria into the abdominal
2. Identify the disease incubation Island. We collected, euthanised and space)
period dissected diseased invasive geckos
to obtain infected tissue. We then • Skin incision (where we placed
3. Test the effectiveness of five bacteria onto a shallow skin
inoculated this infected tissue into
potential antibiotic treatments incision)
25 Asian house geckos randomly
4. Determine whether any of the
allocated to the following five • Mucosal incision (where we
five antibiotic treatments have
groups (5 geckos per group). placed bacteria onto a shallow
prophylactic application
• Subcutaneous (where we incision inside the moist lining
injected bacteria under the skin) of the mouth)
What we did (continued)
A control group was also used in
the trial, five healthy Asian house
geckos were injected with sterile
saline solution instead of the
bacterial inoculation.
We also wanted to investigate
whether direct contact could
cause infection, so we housed an
additional five Asian house geckos
individually with a diseased gecko.
We then monitored all geckos in Asian house gecko being examined to determine the effectiveness of antibiotic treatments
the trial twice weekly for three during the trial. Image: Jessica Agius
months to track the timing of
the development of disease. • Rifampicin To further analyse the effectiveness
• Clarithromycin of enrofloxacin and our trialled
The treatment trial dosage as an antibiotic treatment
Geckos that went on to develop A sample size of three animals for this disease, we dosed 24
disease in the infection trial were per treatment group was used. healthy invasive geckos once
then randomly allocated to five All animals were dosed orally with enrofloxacin. We collected
groups, which were administered once a day for a total of 21 days, blood plasma at 0, 1, 2, 6, 12,
the following antibiotic treatments: and the progress of disease 24, 48 and 72 hours following
was tracked by observing and administration of the antibiotic
• Enrofloxacin
photographing the treated geckos to determine whether adequate
• Enrofloxacin combined with twice weekly. At the end of the concentrations of the antibiotic
amoxicillin clavulanic acid treatment period, all geckos had been reached in the blood
• Amoxicillin clavulanic acid were examined to determine the plasma to kill the bacteria.
effectiveness of the antibiotics.
Key findings
The infection trial likely to be infected for quite long The treatment trial
The experimental infection of geckos periods before they develop The majority of the antibiotics we
with the Enterococcus bacteria was visible signs of disease. administered to geckos in this trial
successful, with all groups, except Signs of disease occurred earlier showed some degree of success.
the control group and under-the- in animals that were given the In geckos with advanced head
skin (subcutaneous) injection group, bacteria through incisions to the lesions and evidence of disease
producing visible signs of disease. skin and oral mucosa (moist inner spread throughout the organs,
These results indicate that infection lining of the mouth), in contrast bones and/or tissues, 21 days of
likely starts through bite wounds or to those where the bacteria were antibiotic treatment did not result in
some other form of direct contact. dropped into the mouth or injected. cure. Geckos with skin lesions at a
This indicates that breaks in the skin less advanced state of the disease
The incubation period, or time
or in the mucosal barriers may allow responded better to treatment, and
taken for visible signs of disease to
the bacteria to be more effective were completely cured in one case.
develop, varied significantly between
at establishing disease; and this Although the majority of antibiotic
infection groups, ranging from 50
likely also explains the shorter treatments resulted in the signs of
to 100 days. This long incubation
incubation periods we observed disease lessening following 21 days
period indicates that this disease
in animals from these groups. of treatment, complete resolution
progresses slowly, with animals
of the disease nevertheless was rare.
LEFT: Lesion regression of an Asian house gecko
receiving antibiotic treatment for infection
with E. lacertideformus. Image: Jessica Agius
BELOW: Necropsy of an Asian house gecko
affected with E. lacertideformus. A number
of white lesions containing the bacteria
throughout the liver are evident.
Image: Jessica Agius
Key findings (continued)
This finding may be to do with the or disappearing in one case. We
capsule surrounding the bacteria. conducted an analysis of this
This capsule likely prevented the antibiotic in plasma over time, which
lizard’s immune system from revealed that the concentration we
recognising the bacteria, and also administered likely reached plasma
prevented the antibiotics from concentrations that were sufficient
inhibiting it. to kill Enterococcus lacertideformus.
However, the presence of the
On the basis of what we could capsule surrounding the bacteria
observe visually of the disease, the may hinder the effectiveness of
antibiotic enrofloxacin was most enrofloxacin, and a higher dose
successful, with the highest degree or more frequent dosage may
of the disease signs lessening be required for cure.
Implications and recommendations for future work
The findings from this trial provide and the frequency and duration threat of this disease to the captive
important information about the of antibiotic use ensured a full population of Critically Endangered
pathology and treatment of the and effective course was given. Christmas Island reptiles, and
novel Enterococcus bacterium Additionally, waste was incinerated possibly reduce its spread to
that has led to the death of many and all animals were euthanised and other regions. It is thus beneficial
Extinct in the Wild lizards on were not released back into the wild, to the long-term conservation
Christmas Island. therefore, this trial did not pose a risk of these species.
for the development of resistance.”
The trial indicated that antibiotic Further analyses are underway to
treatments may aid in regression These findings are of relevance to evaluate the total effectiveness of
or complete cure of the disease Christmas Island National Park and each antibiotic. This will involve
(in one animal), and that of the captive breeding program staff, in microscopic examination of
five antibiotics trialled, enrofloxacin addition to quarantine/biosecurity the tissues of animals in the trial
was the most effective. officers and wildlife disease and following 21 days of antibiotic
conservation scientists. treatment to determine the extent
Although this trial did incorporate
two antibiotics with a high Australian By informing disease management of internal disease. This work will
importance rating, only a small and biosecurity protocols this further add to our understanding
number of animals were treated, new knowledge can reduce the of this disease and how to treat it.
Further reading
This factsheet summarises key findings from the following scientific papers. Please refer to the
Further Information papers for more detail.
Rose, K., Agius, J., Hall, J., Thompson, P., Eden, J. S., et al. 2017. Emergent multisystemic
Jessica Agius Enterococcus infection threatens endangered Christmas Island reptile populations. PLOS ONE
jessica.agius@sydney.edu.au 12(7): e0181240. https://doi.org/10.1371/journal.pone.0181240
Agius, J., Rose, K., Emery, J-P., & Phalen, D. 2021. Experimental infection of Asian house geckos
(Hemidactylus frenatus) with Enterococcus lacertideformus demonstrates multiple routes of
disease transmission and the relative in-vivo efficacy of antibiotic treatments. Scientific Reports.
Cite this publication as NESP Threatened Species Recovery Hub. 2021. Understanding and treating a
new Enterococcus bacterial infection affecting Christmas Island lizards, Research findings factsheet.
This project is supported through funding from the Australian Government’s National Environmental
Science Program.You can also read
