MyiasisBy Karma TibergBiology 4800Spring 2011

Outline

•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 body-substance, 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

•Nasopharyngeal•Opthamomyiasis•Oral • Intestinal•Cerebral

Cutaneous

1. Furuncular▫ 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 Human botfly - Dermatobia hominis (family Oestridae) Tumbu fly – Cordylobia anthropophaga (family

Calliphoridae) *Wohlfahrtia vigil – (family Sarcophagidae)

Furuncular myiais

Cutaneous2. Creeping Myiasis

▫ Infection of humans by the larvae of horse bot flies (Gasterophilus) and cattle bot flies (Hypoderma)

Both in the family Oestridae

▫ Larvae typically do not develop in humans

▫ Travel around the epidermis looking for proper host cues Painful “Migrating lumps” and the production of long tunnels

▫ Gasterophilus tunnels are located in the epidermal layer

▫ Hypoderma tunnels are located deep in subcutaneous tissue but may migrate to other tissues

Cutaneous3. Wound Myiasis

▫ 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 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• 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