Parasite: Myiasis

 

Introduction to Myiasis

 

Photo Credit: Dalius Baranauskas

 

When maggots are mentioned, what do you think of? Creepy, crawly critters in horror movies that feed on dead flesh? You would be correct, but maggots can feed on live tissue, too. The infestation of live tissue with fly larvae (or maggots) causes the disease myiasis.

 

Myiasis (pronounced my-eye-a-sis) can be defined as “the infestation of live human tissue and vertebrate animals with dipterous larvae, which, at least for a certain period, feed on the host’s dead or living tissue, liquid body substances, or ingested food” [1]. And what are dipterous larvae, you ask? Dipterous larvae refer to larvae of flies belonging to the order Diptera.

 

Myiasis is a serious problem for the livestock industry, causing severe economic losses worldwide [2]. Although infestation by fly larvae is much more prevalent in animals, it is a relatively frequent occurrence in humans in rural, tropical and subtropical regions as well [3].

 

Myiasis can come in all sorts of variations, depending on the fly species and where the larvae are located. Some flies may lay eggs in open wounds, other larvae may invade unbroken skin or enter the body through the nose or ears, and still others may be swallowed if the eggs are deposed on the lips or on food [3].

 

What’s in a name?

In Greek, myia = fly.

Myiasis is also known as “fly-strike” and “fly-blown.”

 

Classification and Taxonomy

 

Myiasis-causing flies belong to the order Diptera, known as “true flies.” These flies possess a single pair of wings, distinguishing them from other flies.

 

There are three major families of myiasis-producing flies [4]:

1) Oestridae (bot and warble flies)

2) Calliphoridae (blowflies)

3) Sarcophagidae (fleshflies)

 

Different forms of myiasis are classified according to the parasite-host relationship. That is, whether the fly larvae need to develop in live tissue or not. When we classify myiasis this way, we come up with three different types: specific myiasis, semispecific myiasis, and accidental myiasis [3].

 

Specific Myiasis: Caused by flies that require a host for larval development

 

Fly Species (or Genus)

Common Name

Dermatobia hominis

Human Botfly

Cordylobia anthropophaga

Tumbu fly

Oestrus ovis

Sheep botfly

Hypoderma

Cattle botflies or ox warbles

Gasterophilus

Horse botfly

Cochliomyia hominivorax

New world screwworm fly

Chrysomyia bezzania

Old world screwworm fly

Auchmeromyia senegalensis

Congo floor maggot

Cuterebra

Rodent and rabbit botfly

 

Semispecific Myiasis: Caused by flies that usually lay their eggs in decaying animal or vegetable matter, but that can develop in a host if open wounds or sores are present

 

Fly Genus

Common Name

Lucilia

Green-bottle fly

Cochliomyia

Blue-bottle fly

Phormia

Black-bottle fly

Calliphora

Blowfly

Sarcophaga

Flesh fly or sarcophagids

 

Flesh flies, or sarcophagids, can cause intestinal myiasis in humans if the females lay their eggs on meat or fruit [3].

 

Accidental Myiasis (also called “pseudomyiasis”): Caused by flies that have no preference or need to develop in a host but that will do so on rare occasions. Transmission occurs through accidental deposit of eggs on oral or genitourinary openings, or by swallowing eggs or larvae that are on food.

 

Fly Species (or Genus)

Common Name

Musca domestica

Housefly

Fannia

Latrine flies

Eristalis tenax

Rat-tailed maggots

 

Below are 18 different myiasis-causing flies (adults, of course)!

 

Photo Credit: MJR Hall. “Screwworm flies as agents of wound myiasis.”

 <http://www.fao.org/DOCREP/U4220T/u4220T07.htm>.

 

See fly #8? This fly is Cordylobia anthropophaga, better known as the tumbu fly. Other names include the mango fly, skin maggot fly, and verde cayor. C. anthropophaga has been endemic in the subtropics of Africa for more than 135 years [5] and is a common cause of myiasis in humans in the region. Its name gives us a pretty good clue of what C. anthropophaga is known for: anthropophaga is derived from the Greek word anthropophagus, which means “eater of men.”

 

Because so many factors differ among fly species, such as transmission, clinical presentation, reservoirs, and incubation periods, the tumbu fly will be used throughout the rest of the site as the main example of a myiasis-causing fly species.

 

History of Discovery

 

The Reverend F.W. Hope coined the term myiasis in 1840 to refer to diseases resulting from dipterous larvae as opposed to those caused by other insect larvae (the term for this was scholechiasis). Hope described several cases of myiasis from Jamaica caused by unknown larvae, one of which resulted death [6].

 

Even though the term myiasis was first used in 1840, the disease has been around for far longer than that. In fact, the first account of human myiasis is in the Bible, where Job complains, “My body is clothed with worms and scabs, my skin is broken and festering.” Ambroise Paré, the chief surgeon to Charles IX and Henri III, observed that maggots often infested open wounds [1].

 

Since this site is focusing on the tumbu fly, Cordylobia anthropophaga, it is perhaps important to note that the larvae of the tumbu fly were first described in Senegal in 1862, and Blanchard first described the adult and gave it its name in 1893. In 1903, Grunbert placed the tumbu fly in a new genus, Cordylobia [7].

 

Dipterous fly larvae are not only known for unwanted disease; maggots have historically been used for good as well! They have a long history of being used to clean away dead tissue in wounds, something that is today called maggot therapy. This will be explored more in-depth in the “Medicinal Maggots” section.

 

Clinical Presentation

 

How myiasis affects the human body depends on where the larvae are located. Larvae may infect necrotic (dead) or living tissue in various sites: the skin, eyes, ears, stomach and intestinal track, or in genitourinary sites [8]. They may invade open wounds and lesions or unbroken skin. Some enter the body through the nose or ears. Larvae or eggs can get to the stomach or intestines if they are swallowed with food and cause gastric or intestinal myiasis [3].

 

Yikes! It seems like maggots can get anywhere! Well, yes, that’s why there are so many different clinical presentations of myiasis. However, most cases are not life threatening and can be cured quite easily by simply removing the larvae.

 

A few different presentations of myiasis and their symptoms [3]:

 

Cutaneous Myiasis: Painful, slow-developing ulcers or furuncle- (boil-) like sores that can last for a prolonged period.

 

Nasal Myiasis: Obstruction of nasal passages and severe irritation. In some cases facial edema and fever can develop. Death is not uncommon.

 

Aural Myiasis (in the ear): Crawling sensations and buzzing noises. Smelly discharge is sometimes present. If located in the middle ear, larvae may get to the brain.

 

Ophthalmomyiasis (in the eye): Fairly common, this causes severe irritation, edema, and pain.

 

Nosocomial Myiasis: This is not a specific type of myiasis but rather refers to myiasis in a hospital setting. Unfortunately it is quite frequent, as patients with open wounds or sores can be infested if flies are present. To prevent nosocomial myiasis, hospital rooms must be kept free of flies.

 

The following series of photos show a 5 year old patient receiving treatment for myiasis in his eye (ophthalmomyiasis). The larva extracted is bottom right:

 

Photo Credit: http://en.wikipedia.org/wiki/Myiasis

 

C. anthropophaga rarely causes severe problems, and mainly causes cutaneous myiasis. Geary et al. describe the presentation of cutaneous myiasis caused by the tumbu fly: “At the site of penetration, a red papule forms and gradually enlarges. At first the host may experience only intermittent, slight itching, but pain develops and increases in frequency and intensity as the lesions develop into a furuncle. The furuncle’s aperture opens, permitting fluids containing blood and waste products of the maggot to drain”[9].

 

This photo shows a typical furuncle caused by a tumbu fly larva:

 

Photo Credit: http://www.warrenphotographic.co.uk/wphtm/insects/0602.html

 

CA: Transmission

 

Female tumbu flies lay their eggs in soil contaminated with feces or urine or on damp clothing or bed linens. Damp clothing hanging to dry makes for a perfect spot! The larvae hatch in 2-3 days and attach to unbroken skin and penetrate the skin, producing swelling [3]. If the larvae hatch in soil, any disturbance of the soil causes them to wiggle to the surface to penetrate the skin of the host [9].

 

This drawing shows a female tumbu fly as well as a larva within the skin of the host.

Photo Credit: Chopra, A., Probert, A.J., and Beer, W.E. “Myiasis due to Tumbu Fly.” The Lancet (1985): 1165.

 

CA: Reservoirs

 

A reservoir is defined as an organism that can harbor a pathogen indefinitely with no ill effects. Although C. anthropophaga larvae can cause ill effects for animal hosts, because we are talking about myiasis in humans, we will consider any animal hosts as reservoirs.

 

Many animals are hosts of C. anthropophaga. The dog is the most common domestic host and several species of wild rats are the preferred field hosts. Domestic fowl are dead-end hosts, meaning that the larvae cannot develop when they enter the tissue of fowl [7].

 

Humans are in fact accidental hosts, which means that tumbu fly larvae do not usually infect humans and we are not necessary for the transmission cycle of the fly [5].

 

CA: Vector

 

A vector is an organism that carries the parasites (the larvae) from one host to another. The tumbu fly itself is the vector in a loose sense, because the female deposits the eggs in soil or on damp cloth, where the larvae can hatch and attach to human or animal skin [3].

 

The adult tumbu fly:

 

Photo Credit: Natural History Museum, London

 

CA: Incubation Period

 

After the young larvae penetrate the skin of the host, they take 8-12 days to develop into the prepupal stage and then leave the host to pupate. While in human skin, the larva grows through three different larval stages [8].

 

CA: Morphology

 

C. anthropophaga larvae are 11-15 mm long with 3 curved slits as respiratory openings and numerous small black spines [9].

 

A drawing of a tumbu fly larva:

Photo Credit: K.G.V. Smith (ed). “Insects and Other Arthropods of Medical Importance.” British Museum, London (1973).

 

…And the real thing!

 

Photo Credit: Department of Agriculture Western Australia, photographed by Rebecca Graham

 

CA: Life Cycle

 

Female tumbu flies deposit 100-300 eggs in sandy soil often contaminated with animal feces. The hatched larvae can remain viable in the soil for 9-15 days until they need to find a host for development [8]. If a larva finds a host, it will penetrate the skin and take 8-12 days developing through three larval stages before it reaches the prepupal stage. It will then leave the host, drop to the ground, bury itself, and pupate. It then becomes an adult fly able to reproduce and begin the cycle all over again [9].

 

Below is a simplified version of the blow fly life cycle. The life cycle is the same as that of the tumbu fly, which is also a member of the family Calliphoridae and therefore can be considered a blow fly. The times between stages differ for different fly species.

 

 

Below is another life cycle particular to the tumbu fly, with times between stages noted:

 

Photo Credit: Geary, M, Bernard, H, Russel, R, and Hardy, A. “Exotic myiasis with Lund’s fly.” Medical Journal of Australia 171 (1999): 654-655.

 

The life cycle below is also specific to the tumbu fly. It’s a bit simpler, but note the rat and cat next to the human. These are important animal hosts for C. anthropophaga!

 

Photo Credit: Ockenhouse, Christian, Samlaska, Curt, Benson, Paul, Roberts, Lyman, Eliasson, Arn, Malane, Susan, and Menich, Mark. “Cutaneous myiasis caused by the African tumbu fly.” Archives of Dermatology 126 (1990):199-202.

 

CA: Diagnostics

 

First of all, it’s important to get a travel history. Myiasis is often misdiagnosed in the United States because it is extremely rare and its symptoms are not specific. Intestinal myiasis and urinary myiasis are especially difficult to diagnose [3].

 

Cutaneous myiasis caused by the tumbu fly should be suspected when a patient who has just spent time in Africa presents with ulcers or boil-like sores. A definitive diagnose can only be made when the larvae are found. They should be removed and allowed to develop into adult flies for identification purposes [3].

 

Listed are some clues that you should suspect myiasis: recent travel to an endemic area, one or more non-healing lesions on the skin, itchiness, movement under the skin or pain, discharge from a central punctum (tiny hole), or a small, white structure protruding from the lesion [5].

 

CA: Management and Therapy

 

In cases of cutaneous myiasis, the larvae are most often removed without an incision. Applying Vaseline to the skin blocks the breathing hole and cuts off the larva’s air supply. This will force the maggot to the surface of the skin as it searches for air. The larvae can then easily be extracted from the skin. If this does not work, local anesthetic can be administered and an incision is made to extract the maggot [9].

 

Below shows the removal of larvae from furuncles 15 minutes after applying Vaseline:

 

Photo Credit: Ockenhouse, Christian, Samlaska, Curt, Benson, Paul, Roberts, Lyman, Eliasson, Arn, Malane, Susan, and Menich, Mark. “Cutaneous myiasis caused by the African tumbu fly.” Archives of Dermatology 126 (1990):199-202.

 

Patients should be monitored for additional and subsequent lesions as development does not occur all at once and some larvae may take longer to reach the prepupal stage [9]. To prevent bacterial infection after removal of the larvae, antibiotics can be administered [1].

 

CA: Epidemiology

 

Myiasis has a worldwide distribution, but is most often seen in young children, the elderly, and the physically or mentally infirm, in cases of personal neglect or in places of high fly density [1]. Risk factors include living in rural regions and close contact with domestic animals on a regular basis [3]. Myiasis is common in domestic and wild animals all over the world [3], but is accidental and rare in humans [8].

 

The tumbu fly is endemic to the tropical regions of Africa, south of the Sahara desert. Myiasis caused by C. anthropophaga is the most common cause of myiasis in Africa but can be seen worldwide because of air travel, as human movements carry infestation outside endemic areas [3].

 

In the map below, the distribution of C. Anthropophaga is between the dotted lines. The shaded areas show the distribution of C. rodhani, another species in the same genus.

 

Photo Credit: Geary, M, Bernard, H, Russel, R, and Hardy, A. “Exotic myiasis with Lund’s fly.” Medical Journal of Australia 171 (1999): 654-655.

 

CA: Public Health and Prevention Strategies

 

To prevent myiasis, there is a need for general improvement of sanitation, personal hygiene, and extermination of the flies by insecticides. Clothes should be washed thoroughly, dried away from flies, and ironed. The heat of the iron kills the eggs of myiasis-causing flies [5]. This is especially important for the prevention of myiasis caused by the tumbu fly, as the flies tend to lay their eggs on damp clothing.

 

The Iron: A Secret Weapon in the Fight Against Myiasis!

 

 

Medicinal Maggots

 

Maggots are not always the bad guys: if controlled, myiasis can actually have medical benefits! Fly larvae that feed on dead tissue can clean wounds and may reduce bacterial activity and the chance of a secondary infection. They dissolve dead tissue by secreting digestive enzymes onto the wound as well as actively eat the dead tissue with “mouth hooks,” two probing appendages near their toothless mouth [13]. This is called maggot therapy (alternative names include maggot debridement therapy, or MDT, larval therapy, and biosurgery). A substance in the maggot’s salivary gland has the ability to kill bacteria and promote healing [3]. Maggot therapy has been found to be effective, safe, and simple.

 

Maggot therapy has a long history. The indigenous people of Australia used maggot therapy, as well as the Hill Peoples of Northern Burma, and possibly the Mayans of Central America [3]. Surgeons in Napoleon’s armies recognized that wounded soldiers with myiasis were more likely to survive than those without the infestation. In the American Civil War, army surgeons treated wounds by allowing blowfly maggots to clean away the decayed tissue.

 

In the picture below, maggots can be seen infesting a gangrenous wound on the heel. Some of the black, dead tissue remains, but healthy red tissue is noticeable where the maggots have been eating:

 

Dr. William Baer, an orthopedic surgeon at Johns Hopkins during the late 1920s, used maggot therapy to treat a series of patients with osteomyelitis, an infection of bone or bone marrow and published his findings. Dr. Baer first got the idea when, during World War I, two soldiers presented to him with broken femurs after having lain on the ground for seven days without food and water. Dr. Baer could not figure out why neither man had a fever or signs of sepsis, and he got an unexpected surprise: “On removing the clothing from the wounded part, much was my surprise to see the wound filled with thousands and thousands of maggots, apparently those of the blow fly. The sight was very disgusting and measures were taken hurriedly to wash out these abominable looking creatures.” However, he then realized that the wounds were filled with “beautiful pink granulation tissue” and were healing well. Dr. Baer was onto something that many had discovered before him: the healing power of maggots [11].

 

The following picture shows a wound before and after maggot therapy. Notice how well it has healed!

 

Maggot therapy was common in the United States during the 1930s. However, during the second half of the twentieth century, after the introduction of antibiotics, maggot therapy was only used as a last resort for very serious wounds [3]. Lately maggots have been making a comeback due to the increased resistance of bacteria to antibiotics.

 

Although maggot therapy has been used in the US for the past 80 years, it was approved by the FDA as a “medical device” only in 2004 (along with leeches in the same year) [12]. Maggots were the first live organism to be marketed in the US according to FDA regulations, and are approved for treating neuropathic (diabetic) foot ulcers, pressure ulcers, venous stasis ulcers, and traumatic and post-surgical wounds that are unresponsive to conventional therapies. Before this, maggots were being used but were unregulated. Richard Sherman, a doctor in Irvine, CA, is the most well-known maggot therapy advocate and began treating patients with maggots in 1990 [12]. He is now the laboratory director of Monarch Labs, the first and only commercial producer of medical grade maggots. This lab has provided maggots and maggot therapy supplies since 1935 [14].

 

 

The photo below shows medicinal maggots applied to dead tissue in an ulcer on the leg:

 

Photo Credit: Sherman, RA, Hall, MJR, and Thomas, S. “Medicinal Maggots: An ancient remedy for some contemporary afflictions.” Annual Review of Entomology 45 (2000):55-81.

 

Today, there is an ever-increasing demand for medical maggots. In the US, demand for these fly larvae has increased by 20% over the last ten years, and doubled since the FDA ruling. Maggot therapy is now used in more than 300 sites across the country [13]. The American Medical Association and Centers for Medicare and Medicaid Services recently clarified the reimbursement guidelines to the wound care community for medicinal maggots, and this therapy may soon be covered by insurance [10]. The species most widely used for maggot therapy is Lucilia sericata, the green-bottle blowfly. The species chosen for maggot therapy must not feed preferentially on living tissues; L. sericata starve on live tissue and therefore work well for this purpose. Medicinal maggots are placed on the wound and covered with a sterile dressing of gauze and nylon mesh. Too many larvae placed on the wound could result in healthy tissue being eaten [1].

 

Want some medical maggots of your very own? It’ll set you back $98 (and a prescription). Below is part of the Monarch Labs order form:

 

 

Web Links

 

Have a larva specimen that you can’t identify? The Natural History Museum in London has a handy interactive key to help you identify the larva that has been causing you problems. If you don’t have a specimen, it’s still cool to have a look!

http://www.nhm.ac.uk/research-curation/research/projects/myiasis-larvae/key/

 

Check out the website of Monarch Labs, the first and only commercial producer of medical grade maggots. There are plenty of videos to watch, including one that shows how to apply a maggot therapy dressing.

www.monarchlabs.com

 

National Geographic has an informative video on maggot therapy:

http://video.nationalgeographic.com/video/player/places/culture-places/work/us_maggots.html

 

Watch a video of tumbu fly larvae being removed from the breast of a Nigerian woman:

http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=394335&blobname=1471-2482-4-5-S1.mpg

 

References

 

[1] Sherman, RA, Hall, MJR, and Thomas, S. “Medicinal Maggots: An ancient remedy for some contemporary afflictions.” Annual Review of Entomology 45 (2000): 55-81.

 

[2] Otranto, Domenico. “The immunology of myiasis: parasite survival and host defense strategies.” Trends in Parasitology 17 (2001): 4.

 

[3] John, David and Petri, William. Markell and Voge’s Medical Parasitology: 9th Edition. Missouri: Saunders Elsevier, 2006. p. 328-334.

 

[4] Hall, Martin and Wall, Richard. “Myiasis of Humans and Domestic Animals.” 1995. Advances in Parasitology 35 (1995): 257-334.

 

[5] Adisa, Charles and Mbanaso, Augustus. “Furuncular myiasis of the breast caused by the larvae of the Tumbu fly (Cordylobia anthropophaga).” BMC Surgery 4 (2004): 5.

 

[6] “Introduction to Myiasis.” The Natural History Museum of London. <http://www.nhm.ac.uk/research-curation/research/projects/myiasis-larvae/intro-myiasis/index.html>.

 

[7] Rice, Paul and Gleason, Neva. “Two cases of myiasis in the United States by the African tumbu fly, cordylobia anthropophaga.” The American Journal of Tropical Medicine and Hygiene 21.1 (1972): 62-65.

 

[8] Ockenhouse, Christian, Samlaska, Curt, Benson, Paul, Roberts, Lyman, Eliasson, Arn, Malane, Susan, and Menich, Mark. “Cutaneous myiasis caused by the African tumbu fly.” Archives of Dermatology 126 (1990):199-202.

 

[9] Geary, M, Bernard, H, Russel, R, and Hardy, A. “Exotic myiasis with Lund’s fly.” Medical Journal of Australia 171 (1999): 654-655.

 

[10] Lloyd, Robin. “ Insurance may soon cover maggot therapy.” MSNBC 19 Nov. 2008 <http://www.msnbc.msn.com/id/27808424/>.

 

[11] Baer, William. “The treatment of chronic osteomyelitis with the maggot (larva of the blow fly).” Journal of Bone and Joint Surgery 13 (1931): 438-475.

 

[12] Rubin, Rita. “Maggots and leeches: Good medicine.” USA Today 7 July 2004 < http://www.usatoday.com/news/health/2004-07-07-leeches-maggots_x.htm>.

 

[13] Greer, Kathleen. “Age-old therapy gets new approval.” Advances in Skin & Wound Care. January/February 2005.

 

[14] Maggot Therapy Project. Ed. Ronald Sherman. 2009. University of California Irvine Department of Pathology. 2 Feb. 2009 <http://www.healthaffairs.uci.edu/som/pathology/sherman/home_pg.htm>.