Myiasis: All you need to know
Myiasis means the infestation of live human and vertebrate animals with larvae, which feed on the host’s dead or living tissue, liquid body substances, or ingested food for some period of time. The vertebrates usually involved are mammals, birds, amphibians and reptiles, but a case of aquarium fish (Asryanax mexicanus fasciatus,Mexican tetra) was infested in the stomach by Calliphora.
Classification of myiasis
Infestations of the head passages
Detrimental- Myiasis , Beneficial- Maggot therapy
Detrimental- Food spoilage, beneficial- Nutrient recycling and forensic
Adopting the parasitological classification, we will consider three main groups of myiasis-producing species: obligatory parasites, which must develop on live hosts and facultative parasites, which can develop on both living and dead organic matter and can be divided into two groups, the primary species which are able to initiate myiasis and the secondary species which occur after obligate or primary species have initiated it fourth grouping, the accidental myiases or pseudomyiases occur when fly eggs or larvae are inadvertently swallowed.
In a controlled experiment, nausea, vomiting, intestinal cramps and diarrhoea were observed in volunteers who swallowed live larvae of Musca domes- tics, Calliphora or Sarcophaga in gelatine capsules Naturally acquired accidental intestinal infestations can show similar symptoms or be benign.
Myiasis in humans
Fly on Skin
Miscellaneous myiases are often reported, particularly in humans, that are essentially accidental but do not involve the intestinal tract. They occur when the wrong host is invaded or eggs are laid in atypical sites for the species. Examples are facultative species involved in human urinary tract myiases, when eggs are deposited at the entrance to the urethra, hatch into larvae and develop at the end of the urethra or inside the urethra or bladder, being passed in the urine Another internal region of the human body that can be unusually infested is the respiratory tract, with relatively mild. human myiasis can be common in parts of the tropics. In humans it can affect oral cavity, skin, penile strutctures, ears etc. This leads to what is called oral , cutaneous, penile myiasis.
Although many authors have reported the clinical and histological features of human infestations with Dermatobia hominis (e.g. Lane et al., 1987), there are few accounts of immunological features. report that there is a complex host immunological response to thelarva, including lymphocytes, eosinophils, activated fibroblasts, mature histiocytes, mast cells/basophils, plasma cells and Langerhans cells. A similar set of cells is found in mice infested by Cuterebra angustifrons.
Immunohistochemistry revealed that the dominant dermal cells responding to the larva were activated T-helper cells which, in turn, probably stimulate plasma cell production and B-cells to produce antibody. The activated fibroblasts produce collagen that may be important in containment of the larva within its fibrous, subcutaneous nodule. The first instar larvae produced the greatest host reaction and allowed the earliest detection of infestation by ELISA. However, the initial immune response against antigens produced by second and third instar larvae was depressed during the course of an infestation, but started to increase as soon as the larvae left their host. This suggests that immunosuppression may be a phenomenon.
Portchinsky (1916) recorded many cases of human infestation with W. mugnca from Russia, with approximately 80% in children of 10 years or less and approximately 70% affecting the ears. Most other cases affected the head area, either eyes, mouth or nose. Human infestations due to W. magnca are still recorded, from the ear (El-Begenny, 1989), eye nose or mouth.
There are basically three levels at which control of myiasis species can be considered:
eliminate the fly species
take care of the wound, dress it properly, take prophylaxis
antibiotics or insecticides can be used
The location of the parasites for much of their developmental stages on the host means that control techniques can be very precisely targeted against at least the larval stage. The precision of targeting and the proportion of the population that can be reached depends on the host specificity of the parasite (i.e. whether there are wild animal, reservoir hosts which cannot be easily treated), and its degree of dependence on the host (i.e. whether or not it is a facultative species that can also develop on carrion).
Historically, control of Dermatobia hominis has been by the application of various insecticides to the hide of livestock, to kill larvae in furuncles and to prevent reinfestation. Applications had to be repeated at two- to four-week intervals to be of benefit. Insecticides used in this manner include toxaphene (camphechlor), DDT/gamma-BHC mixtures, crufo- mate, fenthion and trichlorphon. The intramuscular injection of Closantel (10-12.5 mg kg-‘) has been used for control with success, three injections at regular intervals keeping cattle virtually free of larvae for three to four months.
Ivermectin is very effective for killing larvae of D. hominis in cattle. Doramectin gave at least 35 days protection from infection by first instar larvae. This ability to protect cattle from infestation gives chemicals such as Doramectin a marked advantage over those that are only effective in treating existing infections since, in economic terms, it is more important to prevent hide damage than treat animals with an infection that has already damaged the hide
There is considerable scope for further study of the interactions between agents of myiasis and other parasites of domestic livestock, regarding immunosuppression and the possibility of myiasis making animals more susceptible to other diseases.