Saddam Ahmed sarangzai

1. DERMAL MYIASIS
INTRODUCTION:
Myiasis is the infestation of the organs or tissues of host animals by the
larval stages of dipterous flies, usually known as maggots or grubs. The
fly larvae feed directly on host’s necrotic or living tissue. The host are
usually mammals, occasionally birds and, less commonly, amphibians or
reptiles.
Definition. Myiasis is defined as the infestation of live human and
vertebrate animals by larvae of the order Diptera (true flies i.e. those
whose adult have two wings) that feed for varying time periods on the
host’s dead or living tissue, body substance ,or infested food.
The term myiasis was proposed by Hope in 1840 and stems from Greek
myia meaning a fly
Classification.
Myiasis may be classified into two different ways. The first pertains to
the location of the affected area such as cutaneous, nasopharyngeal,
ocular, intestinal/entric, and urogenital. The second classification
describes the relationship between the host and the parasite such as
obligatory, facultative, or accidental.
Cutaneous myiasis is the most frequently encountered clinical forms
and can be divided further into three main clinical manifestations:
1) Furuncular, 2) creeping (migratory), and 3) wound (traumatic)
myiasis

2. Myiasis –producing flies are members of the superfamily oestrodiae
oestrodiae consist of three major families’ oestridae, calliphoridae, and
sarcophagidae subfamilies of oestridae include oestrinate,
gasterophiliane, hypodermatinae, and cuterebridae, with all species of
this family being obligate parasites The families of calliphoridae and
sarcophagidae contain both obligate and facultative organisms below
are main flies that cause cutaneous myiasis in humans.
1) Furuncular myiasis
Dermatobia hominis
 The larvae that commonly cause human furuncular myiasis are
Dermatobia hominis, Cordylobia anthropophaga, Cuterebra spp.,
Wohlfahrtia vigil, and W opaca.
 D hominis is the most common agent of both cutaneous myiasis
and furuncular myiasis diagnosed in North America.
 D hominis is found in Central and South America and uses a
carrier insect to transport its eggs to the host
Many of the flies that cause furuncular and migratory myiasis are
commonly referred to as ‘‘bot flies’’ or ‘‘warble flies.’’ ‘‘Bot’’ refers to
the maggot itself; ‘‘warble’’ refers to the furuncular lesion formed by the
fly larva. D hominis, commonly referred to as torsalo and the human bot
fly, is the most common agent of cutaneous myiasis diagnosed in
travelers returning to the Unite d States.
Figure 2 Furuncular-like nodules on shoulder caused by Dermatobia hominis myiasis
Figure 1 Dermatobia hominis fly

3. the life cycle of D hominis is complex. The adult D hominis female lays
her eggs directly onto foliage or onto captured day-flying mosquitoes,
and, less commonly, onto flies and ticks; the eggs adhere via a quick-
drying adhesive. The eggs are conveyed to the host by direct contact
with foliage or when a mosquito, fly, or tick bites the host. This
characteristic is called ‘‘hitch-hiking’’ or phoresis. At the time of
colonization, the autochthonous inhabitants of D hominis-infested areas
were familiar with the mosquito’s role in the D hominis life-cycle,
because the term gusano de zancudo (‘‘worm of the mosquito’’), was
used to describe the larva. The mature D hominis fly is not commonly
seen by human because of its short 4- to 8-day lifespan and the
method of egg dispersal which avoids vertebrate hosts. All vernacular
names in the languages spoken where the human bot fly is found
describe the larva and sometimes the egg carriers but never the mature D
hominis fly. Although humans are the preferred hosts, dogs, cattle, and
monkeys can also be affected Once in contact with the skin, the host’s
body heat causes the eggs to hatch and the first stage larvae (first
instars*) then painlessly burrow into minute skin perforations, follicular
openings, or unbroken skin. After larval penetration, a small,
erythematous papule develops that later becomes a furuncular-like
nodule.
Skin
Figure 3 Second (solid arrows) and third instar (broken arrows) Dermatobia hominis larvae. Note
the wider cephalad ends, which are located deep in the tissue, and therows of black spines that
resist extraction. When the third instars larva emerges from the skin, it falls to the ground to
pupateand develops into an adult fly.

4. 2) Creeping myiasis – dermal myiasis
Hypoderma.
Creeping myiasis is caused by the larvae of horse and cattle bot flies.
These flies are obligatory myiasis producers, with humans not being the
ordinary host. In humans, the larvae cannot develop further and will
produce tunnels in the epidermis where they may wander for
considerable distances. Two flies that cause creeping myiasis include
Gasterophilus and Hypoderma.
Figure 4 Gadding behavior of calf in response to figure 6 third instars larvae of hypodermae
Hypodermabovis attack. Note theraised tail and kicking up of
the heels of the hind legs
Hypoderma spp. Cause significant economic impact because of the
reduction in milk production, weight loss, damage to hides, and carcass
depreciation caused by trimming of the diseased areas. An ongoing
eradication program in Europe using avermectin, a systemic larvicide,
has been highly successful. The flies of the Hypoderma spp. that infest
cattle are known as heel flies, gad flies, and cattle grubs. H bovis, known
as the northern cattle grub, is established in most locations in the
northern hemisphere. It has not become permanently established
in the southern hemisphere and cases reported from Australia, southern
Africa, and South America

5. 3) Wound (traumatic) myiasis
Screwworm flies
New World and Old World screwworms, respectively, are two
important species of screwworm flies that cause obligatory wound
myiasis in humans, domestic mammals, and wild mammals. The
distribution of the C. hominivorax, the New World screwworm, once
extended from the US to southern Brazil but massive state, federal, and
international eradication programs have made their appearance in these
areas rare. They are currently located in the areas of South and Central
America
Screwworm infestations are rare in humans but can become fatal
because of two compounding factors: (i) screwworms may travel
through living tissue and are not confined to the subdermal layer, and (ii)
eggs are laid in batches of 150–500 eggs resulting in multiple
infestations within the host and wounds containing up to 3000
larvae.5,30 Females of both species are attracted to mammalian wounds
and will lay their eggs at the edge of the lesion.5 The large batch of eggs
will then hatch approximately 15 h later and will feed on living tissue
during their entire larval period.5 Lesions 4–5 cm deep are rapidly
produced and a characteristic odor is given off that will attract gravid
flies to lay additional batches of eggs at the infestation site.30
Prevention
most infestations can be avoided if proper precautions are observed.
Keeping the responsible fly, mosquito, or tick from reaching the skin is
paramount. Using window screens and mosquito netting, insect
repellents and insecticides, and good skin and wound hygiene can
prevent skin contact. Adequate skin covering and the use of proper

6. clothing is likewise important. Open wounds should always be covered,
and dressings should be changed daily. Particularly in the case of tumbu
fly myiasis, drying clothes in bright sunlight, ironing them, or both will
prevent clothes from acting as fomites. Field control of flies, including
mosquitoes via aerial spraying, destruction of animal carcasses, removal
of garbage from around living areas, and practicing standard field
hygiene and sanitation can significantly reduce fly populations
Conclusion
Myiasis in humans can produce furuncular, creeping, or traumatic
lesions. The trauma could range from minor to severe depending on
species and location of infestation. Each fly has a specific geographical
region ranging from the woodlands of North America to the tropical
regions of South America and Africa. Location of the primary
infestation and the physical characteristics of the fly and wound allow
clinicians to aid in the diagnosis. Length, shape, color, life cycle,
number of offspring, and arrangement of spines are all physical
characteristics that differentiate the many different species of larvae and
thus are useful in determining and predicting the severity of infestation.
Treatment is species specific, but may include preventative measures
such as mosquito repellents containing DEET. However, avoiding
exposure is the single best preventative measure. Other treatments may
include, but are not limited to, expression of the larvae after placing an
obstructing substance over the spiracle, irrigation and debridement,
surgical exploration, or topical and/or systemic antibiotics to prevent
secondary infection
REFERENCES
1. Zumpt F. Myiasis in man and animals in the Old World. London: Butterworths; 1965.
2. Hope FW. On insects and their larvae occasionally found in the human body. Trans R Soc Entomol London
1840;2:256.
3. Patton WS. Some notes on Indian Calliphorinae. Part I—
Chrysomya bezziana Villeneuve, the common Indian Calliphorinae whose larvae cause cutaneous myiasis in man
and animal