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Bio Justin 171
Oestridae and Myiasis-based Parasitism in Hosts
Introduction
The family Oestridae consisting of bot flies parasitizes mice by limiting their
reproductive functions and overriding immune system responses of hosts. The subfamilies of
Oestridae are Oestrinae, Gasterophilinae, Hypodermatinae, and Cuterebrinae and are further split
into numerous genera based on the selected host. A few species examined in this paper are
Dermatobia hominis, Cuterebra Fontinella, and Oestrum Ovis. These species inflict on hosts
what is called myiasis, or the invasion and infestation of parasitic larvae in the living or dead
tissues of the host. As a result, myiasis is detrimental and beneficial to the host but is more
advantageous for the parasite as the host provides shelter and nutrition for growing larvae. There
are three methods through which myiasis can occur: Dermal or subdermal, nasopharyngeal, and
intestinal. In dermal or subdermal myiasis, the skin is penetrated and swellings called furuncles
occur. In nasopharyngeal myiasis, the nostrils or mouth are invaded with larvae and the sinuses
are subsequently penetrated. Finally, intestinal myiasis occurs when eggs deposited on the host
are consumed. Hence, myiasis contributes to negative effects on vital rates of mice and other
hosts in host-parasite relationships with D. hominis, C. Fontinella, and other Oestrid species
(Colwell et al. 2006).
Body
Parasitism is defined as a relationship where one benefits at the others expense. Oestrid
larvae are indeed parasitic of mice. Bot fly species C. Fontinella depends on and benefits from
the white-footed mouse (Peromyscus leucopus) to complete the formers life cycle. Relying on
nutrients and proteins of mice hosts to grow, C. Fontinella absorbs these from P. leucopus tissue
after myiasis (infection). On the contrary, the disadvantaged infected hosts change behaviors
such as economizing space, movement, or grooming (Cameron et al. 2006). This is due to the
large size of the parasite relative to the host, which impedes movement in the latter (Cameron et
al. 2009). Likewise, infected P. leucopus consume more mass especially high in protein and
energy (Cameron et al. 2006). This increase in consumption inevitably leads to increased fat
stores which may reduce fitness. In the study conducted by Cramer et al. (2006), male and
female mice weighed 19.1 and 18.2 grams respectively prior to infection then 21.4 and 19.6
grams respectively after infection. Finally, another experiment conducted by de Rosis (2000)
examined the immune reaction in hosts by D. hominis infestation. Infestation increases quantity
of T lymphocytes (Thy+), helper T lymphocytes (CD4+), killer T lymphocytes (CD8+), and B
lymphocytes (CD45), especially in mice that were reinfested after having been purged of first
infestation (Colwell et al. 2006). CD4+ and CD8+ shape the immune response. In general, there
is an accentuated immune response in hosts of D. hominis myiasis, especially to multiple
invasions, which become likelier after a first infestation. These immune responses to Oestrid
infections are seen in the granulomas forming in skins of hosts and require energy from the host
(Cameron et al. 2006).
Bot fly parasitism is known to directly influence the death rates of mice. In the study by
de Rosis (2000) of D. hominis, thirty mice were infested with four to five larvae each and all died
within eighteen days. In another experiment by Leite et al. (2010), mice were artificially
infested with three instars that were taken from another host (Colwell et al. 2006). First-instar
(L1) is larvae that have been implanted in a host for 4 days, second-instar (L 2) is 6-12 days and
third-instar (L3) is 20 or more days. L3 develops when the larvae emerges from the host skin and
becomes an adult. In this experiment, larvae in varying instars are salvaged from a control group
and subsequently implanted into recipient mice. Three of eight mice that received L 2 larvae died
at varying times post-implantation whereas the other living mice successfully developed instars
until molting. Cutaneous scars formed after the emergence of larvae in all live mice (Leite et al.
2010).
Additionally, Oestrosis, defined by numerous amounts of myiasis the across host,
severely hampers the health of the host. Side effects include major nasal discharge which can
cause breathing hindrances and pneumonia if inhaled; these can ultimately lead to death (Colwell
et al. 2006). Lastly, the impaired movement in mice is extremely detrimental to females who
need mobility to access food resources to fuel pregnancy. As a result, fecundity would decrease
because of this (Cameron et al. 2009). Burns et al. (2005) confirms an inverse relationship
between C. fontinella parasitism and P. leucopus fertility.
The economic problem with Oestrid flies lies in infestation of cattle. In the case of
oestrosis of O. ovis in cattle, host movement can be hampered (Cameron et al. 2009).
Additionally, infested cattle are known to produce less milk and grow less mass. Ilchmann
(1986) reports that cattle produced 1.1-4.6 kg less meat, 200-500 g less wool, and 10% less milk
after infestation. In particular, nasopharyngeal myiasis of O. ovis likely leads to death in hosts.
It is for this economic loss that action must be taken against Oestrid flies. Understanding the
myiasis of Oestrid flies and how they produce furuncles can lead to several control methods.
One such method involves introducing bird species, which have been observed to consume
burrowed and emerging larvae (Colwell et al. 2006). Goodrich (1940) and Bauer (1978) both
observed starlings trying to dig out larvae from furuncles on the backs of cattle. Additionally,
Bishopp et al. (1926) discovered that the feeding patterns of robins and farm birds revolve
around larvae that have emerged from furuncles and dropped onto the ground. Finally, Leinati et
al. (1971) introduced chickens into a grazing cattle population and observed the near eradication
of Oestrids from these cattle.
Benefits from introduction of farm birds to a farm environment greatly outweigh the
disadvantages. For one thing, farm birds increase the diversity of livestock on farms while also
removing implanted larvae from cattle. Likewise, farm birds control other pests as well. On the
other hand, farm birds are inexpensive compared to constructing the coop. Food would be
supplied by Oestrid larvae. However, an effective yet less feasible method of controlling Oestrid
fly populations would be the utilization of the Sterile Insect Technique (SIT) used in controlling
the screwworm fly (Cochliomyia hominivorax).
This technique involves releasing a large
number of sterile males into the target population of species. In an attempt to use SIT against
Oestridae, the Joint US-Canada Pilot Cattle Grub Project ultimately failed to control Hypoderma
bovis and H. lineatum primarily because of the costs of producing sterilized males. Additionally,
the only way of acquiring sterile males was in vivo. However, despite the little progress made,
SIT still managed to reduce one of the targeted populations of Oestridae (Colwell et al. 2006).
Conclusion
In conclusion, Oestridae has a clear parasitic effect on host populations and their vital
rates, especially in mice and cattle. By directly killing the host, limiting the hosts fertility, or
impairing behavior vital for fitness, Oestrid larvae demonstrate potential to inflict major damage.
Fortunately, there are feasible methods that can be used to control the spread of these parasites.
Significant questions left unanswered involve the methods of myiasis adapted by some Oestrid
species whose hosts are endangered species. In general, these are unknown species whose
behaviors are unclear (Colwell et al. 2006).
Word Count: 1198
Works Cited
Colwell, D.D., Hall, M.J.R., Scholl, P. J. August 2006. The Oestrid Flies: Biology,
Host-Parasite Relationships, Impact and Management. CABI Publishing, Wallingford,
Oxfordshire, GBR.
Leite, A.C.R., Nascimento, M.F.A., Serafim, L.R. 2010. Implantation of Human Bot Fly
Larvae in Host Skin. Journal of Medical Entomology 47: 95-95.
Cameron, Guy N., Cramer, Michael J. December 2006. Effects of Bot Fly (Cuterebra
fontinella) Parasitism on a Population of White- Footed Mice. Journal of Mammalogy. 87:
1103-1111.
Cameron, Guy N., Cramer, Michael J. July 2009. Effects of Bot Fly Parasitism on
Movements of Permyscus leucopus. American Midland Naturalist. 163(2): 455-462.