[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

CHAPTER 13 The Arthropods
311
TABLE 13-7
Parameter
Mouth parts
Antennae
Body
Wings
Life Cycle Notes
Key Features Used to
Speciate Adult Flies and
Adult Mosquitoes
Description
Presence or absence of hairs
Number of segments
Structures present for piercing
of skin or sucking
Size and shape as a whole
Size and shape of head,
thorax, and abdomen
independent
Color and distribution of hair
Pattern of veins
Flies undergo complete transition from the developmental
stage to a point at which each stage is
morphologically different, a process known as
metamorphosis. Fly larvae emerge from eggs. Fly
life cycles typically contain multiple larval stages.
The formation of a cocoon stage (known as a
pupa) prior to becoming an adult is a standard
occurrence in the fly life cycle. The specific life
cycle of individual fly species may vary. The adult
fly is capable of transmitting a variety of diseases,
parasitic and bacterial, to humans through blood
meals.
Epidemiology and Geography
Flies, in general, are found worldwide. Specific
species of flies are more prevalent in certain
regions than others. The geographic distribution
of the common parasite-transmitting flies
and the specific parasites involved are listed in
Table 13-8.
Clinical Symptoms
Most flies affecting humans in the United States
have been described as biting pests whose main
function may be a concern only of sanitation.
Flies can transmit various bacterial diseases
TABLE 13-8
Species
Parasite-Transmitting Flies:
Geographic Distribution
and Associated Parasites
Geographic
Distribution
Associated
Parasite
Tsetse fly Africa Trypanosoma
rhodesiense
Trypanosoma
gambiense
Sandfly Asia, South America,
Mexico, Central
America, Africa,
Leishmania spp.
Black fly
Mediterranean
Africa, Mexico,
Central and
South America
Onchocerca
volvulus
Deer fly Tropical Africa Loa loa
associated with enteritis caused by crosscontamination
of exposed foods. They may also
actively transmit specific parasites. Relatively few
symptoms are associated with contact with the
fly itself. An irritated and sometimes painful bite
site has been described in some patients. Most of
the symptoms seen are related to the parasite
transmitted and not to the fly bite.
Myiasis refers to humen tissue infestation by
fly larvae (often referred to as bot flies) found in
Central and South America (Dermatobia spp.)
and sub-Saharan Africa (Cordylobia spp.).
Although primarily a problem for livestock,
humans can be accidental hosts. Infection can
occur after the female fly passes her eggs onto
another flying insect, such as a mosquito. Accidental
or opportunistic cases can occur when a
female fly lands on a human host, particularly an
individual with wounds or diseased tissues. The
female fly takes advantage of such situations and
deposits her eggs or larvae. When the mosquito
bites an animal (or human) the eggs hatch and
the larvae, often referred to as maggots, immediately
penetrate the skin. Depending on the species
of fly, the larvae (i.e., maggots) may inhabit the
skin lesion for approximately 2 weeks before
maturing (Cordylobia spp.) or 6 to 12 weeks