Myiasis
By Karma Tiberg
Biology 4800
Spring 2011
Outline
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What is myiasis?
Flies causing myiasis
Life cycle
Effects on livestock
Effects on humans
A few types of myiasis in humans
Treatment options
What is Myiasis?
• Myiasis is the disease caused by the feeding of larval
dipterans on living and necrotic tissue, liquid bodysubstance, or ingested food
• Described in two ways:
▫ Location of the affected area
▫ Relationship between the fly and its host (obligate,
facultative, or accidental)
• Can affect all vertebrates including humans!
The Flies
• There are three main families of flies that cause
myiasis:
▫ Oestridae (obligate parasites)
▫ Calliphoridae (obligate or facultative)
▫ Sarcophagidae (obligate or facultative)
Life Cycle
Effects on Livestock
• Pests that cause huge economic losses worldwide (in
the hundreds of millions annually)
• Cause stress to the livestock and reduction in
livestock health
• High infection levels, or migration of larvae into
important regions can lead to death
• Damage to the hides
Horse and Cattle Bots
Screwworm Flies
Effects on Humans
• Mainly a problem for rural populations especially in tropical and
subtropical regions
▫ A problem of countries with a low socioeconomic status, limited access to
health care, and poor hygienic practices
• A problem for elderly people
• Most commonly infected by obligate and facultative fly species
• Humans may become infected if they spend extended periods of time
around livestock
• Depending on the species of fly and the type of infection, the effects can
range from minor to severe and potentially fatal
• Secondary infections are common
Types of Myiasis in Humans
• Cutaneous
▫ Furuncular
▫ Creeping
▫ Wound
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Nasopharyngeal
Opthamomyiasis
Oral
Intestinal
Cerebral
Cutaneous
1. Furuncular
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Infection of skin on the scalp, face and extremities
Swelling localized at the area of infection
Small opening is maintained in the skin to promote
respiration, and waste excretion by the growing larvae
Mainly a problem in tropical locations, but can be a
problem in the U.S. and Canada
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Human botfly - Dermatobia hominis (family Oestridae)
Tumbu fly – Cordylobia anthropophaga (family
Calliphoridae)
*Wohlfahrtia vigil – (family Sarcophagidae)
Furuncular myiais
Cutaneous
2. Creeping Myiasis
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Infection of humans by the larvae of horse bot flies
(Gasterophilus) and cattle bot flies (Hypoderma)
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Both in the family Oestridae
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Larvae typically do not develop in humans
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Travel around the epidermis looking for proper host cues
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Painful “Migrating lumps” and the production of long tunnels
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Gasterophilus tunnels are located in the epidermal layer
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Hypoderma tunnels are located deep in subcutaneous tissue
but may migrate to other tissues
Cutaneous
3. Wound Myiasis
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Flies deposit eggs or larvae on
the outer margins of a wound or sore
Larvae feed and travel through living flesh
Can be fatal if left untreated
Wound myiasis can develop into other forms of myiasis
depending on where the larvae migrate in the body
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Screwworm Flies - Cochliomyia hominivorax, Chrysomya
bezziana
Wohlfahrtia magnifica (family Sarchphagidae)
Bluebottle flies
Nasopharyngeal
• Less common in humans
• Occurs in people who spend
extended periods of time around livestock
 Sheep bot fly (Oestrus ovis)
• Fly inserts larva into the nostril of host
• Larvae can cause extensive damage to the nose, sinuses and
pharynx due to the feeding on living and necrotic tissue
• In some cases larvae can migrate out of the sinuses into the
eyes, ears, mouth or brain causing myiasis in those locations
Nasopharyngeal
Opthalmomyiasis
• Affects the eyes, orbits and
periorbital tissue
• Larvae cause the destruction of
these tissues through feeding and
migration
• Often caused by migrating fly
larvae or flies that preferentially
infect soft and susceptible tissues
• May lead to blindness if not
treated
Opthalmomyiasis
Oral Myasis
• Infestation of the oral cavity by
fly larvae
 Sheep bot fly
• Migratory larvae, or
opportunistic infection of a sore
or lesion (wound myiasis)
 varejeira fly - Cochliomya
hominivorax
Intestinal Myiasis
• This is often a result of accidental infection
▫ Ingestion of fly eggs or larvae in water or
contaminated food and subsequent larval
development within intestines
• Can be a result of migration of larvae
Cerebral Myiasis
• Extremely rare
• A traumatic skull fracture
followed by the depositing of
eggs or larvae into the wound
 Human bot flies
 Screwworm Flies
• Migration of larvae into the
brain originating from another
area of the body
 cattle bot flies (Hypoderma)
Shoo fly, don’t bother me!
• Preventative measures are usually the best way to minimize
human (or livestock) infection with myiasis
▫ Use of insect repellents with DEET
▫ Improve hygienic practices
▫ Limit exposure to livestock and other common hosts, or
treatment of livestock with insecticides and larvicidal drugs
(endectocides)
▫ Introduction of coprophageous insect species
• Suffocation of larvae within the skin and then careful
extraction of the larvae (Furuncular)
• Treatment with Ivermectin products
• Surgery
References
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Caca, I., K. Unlu, S. Soker Cakmak, K. Bilek, B. Sakalar and G. Unlu. 2003. Orbital myiasis: case
report. Japanese Journal of Ophthalmology 47: 412-414
Colwell, D.D., D. Otranto and J. R. Stevens.2009. Oestrid flies: eradication and extinction versus
biodiversity. Trends in Parisitology 25: 500-504
Lucas, E. M., C. Diez, A. Gutierrez, F. Montiaga, J. Arnaiz, A. Gonzalez Mandly, E. Sanchez and N.
Valle. 2008. Unusual MRI findings in a patient with history of frontal fracture and skin
infestation by fly larvae, as a possible sign of intracerebral myiasis. Clinical Neurology and
Neurosurgery.110: 725-728
Robbins, K. and A. Khachemoune. 2010. Cutaneous myiasis: a review of the common types of
myiasis. International Journal of Dermatology 49: 1092-1098
Shinohara, E. H., M. Z. Martini, H. G. Oliveira Neto and A. Takahashi. 2004. Oral myiasis treated
with ivermectin: Case report. Brazilian Dental Journal.15: 79-81
1999, Intestinal Myiasis caused by Eristalis tenax, Journal of Clinical Microbiology 37: 3082