|
WARNING: This report is not for the
squeamish.
If maggots remind you of fly-blown meat and rotting corpses, think
again. For maggot therapy -- the debridement of necrotic tissue
with sterile fly larvae -- is fast securing a place in wound care.
Early clinical experience suggests it could also be a formidable
weapon against meticillin-resistant Staphylococcus aureus (MRSA).
Maggots clean up wounds beautifully --
a fact known for centuries, especially to military surgeons,
who found that battle wounds accidentally infested with maggots
healed quickly without becoming infected. According to Ronald Sherman
(University of California, Irvine, CA, USA), maggot therapy was
introduced into civilian medicine in the USA in the 1930s but fell
out of favour with the introduction of antibiotics. But maggots
are now making a comeback, especially in the treatment of chronic
wounds infected with antibiotic-resistant bacteria. "Maggots
are often successful where conventional remedies have failed",
says Sherman.
Steve Thomas (Princess of Wales Hospital, Bridgend, UK), who runs
the UK's only commercial unit breeding medicinal maggots, which
supplies 800 centres in the UK and Europe, describes the larvae
as "living chemical factories".
Once applied to the wound, and covered with a fine nylon net (to
prevent escape), the maggots move over the surface "secreting
proteolytic enzymes that break down dead tissue, turning it into
a soup, which they then ingest".
How maggots tackle wound infections is not entirely clear, however.
It has been suggested that ammonia in maggot secretions may partly
account for this antimicrobial effect by raising wound pH, but the
secretions also contain other agents, which Sherman and other investigators
are attempting to purify and characterise. But there is another
and potentially more important mechanism: along with their semiliquid
food, maggots ingest bacteria, which are lysed in their gut.
Maggots Can Deal with a Variety of Wounds
Not all species of maggot are suitable for medical use, because
some attack healthy human tissue. Both Thomas and Sherman use
larvae of the common greenbottle, Lucilia (Phaenicia) sericata.
To breed medicinal maggots, eggs collected from specially bred adult
blowflies are sterilised, then allowed to hatch on fresh liver.
In June, Sherman presented the preliminary results of his prospective
trial of conventional wound care followed by maggot therapy at a
Wound Healing Society symposium in Toronto, Canada. 43
maggot-treated wounds were debrided faster and more completely than
they had been during conventional treatment.
Large, prospective, randomised trials of maggot therapy have been
hampered by lack of funding, but the striking results of one
small trial suggest that maggots can provide a cost-effective alternative
to conventional treatments for necrotic venous ulcers, which involve
considerable nursing time and expense.
In a randomised trial in 12 patients with sloughy venous ulcers,
Michael Walker (West Cumberland Hospital, Whitehaven, UK) found
that maggot therapy debrided the ulcers more quickly and effectively
than standard hydrogel dressings -- all six patients treated with
maggots had their ulcers successfully debrided with a single application,
whereas two of the six hydrogel-treated patients still needed dressings
a month later (J Tissue Viability 2000; 10: 91-94).
Walker calculates that, taking nursing time into account, maggot
therapy costs little more than half as much as hydrogel (UK£78
vs UK£136). Although the trial was small and non-masked, Walker
is "hugely impressed" by the results. The patients happily
accepted maggot therapy, "although a few reported a slight
nipping sensation".
In vitro, live maggots kill or inhibit the growth of a range
of pathogenic bacteria, especially S aureus and group A and B streptococci.
They show some activity against Pseudomonas spp, but none against
Escherichia coli or Proteus spp. "These findings are consistent
with clinical observations that maggots can combat infections in
a variety of wound types, including those infected with antibiotic-resistant
strains", says Thomas.
In fact, Thomas believes that treatment
of wounds infected with MRSA is likely to become a major indication
for the use of maggot therapy in the future. "The
presence of large amounts of necrotic tissue in wounds can prevent
topical antibacterials, such as mupirocin, from reaching the site
of infection", says Thomas. Sterile maggots also obviate the
growing problem of MRSA resistant to other antibiotics in addition
to meticillin. Thomas recently used maggots to treat five consecutive
MRSA-infected lesions (three pressure sores, a pilonidal sinus,
and a large abscess), all of which had failed to respond to many
weeks of treatment with conventional products.
After 48 h of maggot therapy, all lesions were MRSA-negative
and healing well (unpublished results). Thus, Thomas sees the
use of maggots as a cheap, safe, and highly effective method for
managing MRSA-infected wounds without adding to the problems of
antibiotic resistance.
Maggot therapy seems to be catching on more quickly in the UK
than in the USA -- partly because Thomas and his colleagues
have taken "an upbeat approach, lecturing at study days and
conferences, and so on". But Sherman notes that "there
are a lot more patients in the USA requesting maggot therapy than
can find practitioners willing to apply it. There is still a strong
feeling among doctors that it is an antiquated treatment."
However, he adds, US medical insurance companies
do reimburse for maggot therapy.
In the UK, most wounds are treated in primary care, and it would
make sense for maggot therapy to be available to patients in the
community -- especially since both hospital-based and district
nurses find the technique easy to learn. Thomas is optimistic that
the Department of Health will accept his application to have maggot
therapy available on a National Health Service general-practice
prescription. "It would be an enormous benefit for patients",
he says. "The use of maggots can dramatically
reduce treatment times compared with conventional therapies,
and it is very likely that their use at an early stage would reduce
hospital admissions or the need for surgical intervention in the
treatment of certain types of necrotic wounds."
Lancet September 30, 2000; 356:
1174 - 1178
| 