Parasitic Insects
 

Parasitic insects are very important ecologically, medically and economically. A broad definition of parasitic that includes mosquitoes and biting flies would make some 15% of insects parasitic.


Lice
Lice have been a part of human history as parasites without socioeconomic boundries. Archaeologists have even found traces of lice on mummies. These insects are wingless, flattened and have reduced or no eyes. The eggs (nits) are glued to the feathers or hairs of the host and there are three immature forms from egg to adult. There are no free living stages and they die when separated from the host.

Bed bugs
Bugs of the Family Cimicidae are reddish brown, dosoventrally flattened bugs that are rather large (up to 8 mm long) with no wings. They are nocturnal feeders that run very fast. They generally are most active around dawn when they feed on resting hosts. Daytime hiding places include mattress seams or crack in walls or furniture. The bites may cause allergic reactions in some people but generally cause little reaction. Domestic cleanliness and residual insecticides to hiding places is effective in controlling bed bugs.


Reduvid Bugs
These bugs are vectors for Trypanosoma cruzi. These are large winged bugs that live in cracks and crevices of poorly constructed homes or in thatched roofs. They are not picky about the source of their blood meal and will feed on whatever is available in the habitat. Improvements in construction methods, the use of metal rather than thatched roofs and residual insecticides are effective control measures.


Fleas
Of the some 2,000 flea species, most are parasites of mammals. Historically fleas have had a great impact as transmitters of the bacteria (Yersinia pestis) that causes the plague. Fleas are bilaterally flattened, commonly reddish black, and wingless. The adults feed by sucking blood from the host. The larvae feed on debris and flea droppings on the bedding. Fleas are amazing jumpers. For example, common fleas can jump some 33 cm high. The oriental rat flea can jump more than 100 times its body length.

Fleas are not host specific but have preferred hosts. Pulex irritans is the human flea but can be found on dogs, cats, squirrels, pigs, and others. This species can transmit the plague. Ctenocephalides canis and C. felis are the common dog and cat fleas, respectively. Controlling pet parasites can be accomplished by numerous commercially available residual, topical and systemic insecticides.


Flies (Order Diptera) represent the most medically important group of insects. They cause directly or indirectly a million human deaths each year. Some flies do not kill but contribute to disfiguring, debillitating diseases of many kinds either as vectors of pathogenic organisms or as parasites.

Black Flies
Black flies belong to the family Simuliidae and are found worldwide where the females feed on blood as well as plant nectar. Black flies are the vectors of Onchocerca volvulus. Mating occurs in flight, larval development occurs in running water and the flies are therefore numerous near rivers and streams. In the US and Canada, S. venustum are well known to fishermen and campers. Bites may produce little reaction in some people, but often small red itching wheals develop as a local reaction. Sometimes black fly fever can result which is characterized by nausea, headache, fever and swollen limbs.


Sand flies
Most sand flies do not affect humans, but rather parasitize reptiles and amphibians. However, some do feed on birds and mammals, including humans. Females take a blood meal in addition to plant fluids. Males eat only plant juices. Most are night time feeders due to the need to avoid hot desiccating environments. They are good vectors of disease and participate in leismaniasis, bartonellosis and some viral diseases.


Biting midges (no-see-ums)
These very small flies (less than 1 mm) are mostly daytime feeders that are most obnoxious on calm days as winds easily carry them away. Only females feed on blood. They act as vectors for various protozoal and viral disease of domestic animals.


Mosqutoes
Some 300 species of mosquitoes have been described with at least 150 of these being in N. America. The life cycle of mosquitos requires water for the larval and pupal stages. Adult females can live for 4-5 months but during the height of the summer season they may only live a couple weeks. Males may live only for weeks to a month. Species of mosquito transmit western equine encephalitis, St. Louis encephalitis, filarial worms, yellow fever, dengue fever, eastern encephalitis and malaria.


Tsetse flies
These flies of the Glossina species are found in Africa where they are vectors of sleeping sickenss. They are daytme feeders that are visually attracted to moving objects. Both sexes feed exclusively on blood, including that of humans.


Ticks
These epidermal parasites are found in nearly every country in the world. Their importance as agents and vectors of disease has long been recognized. Pathogenesis appears in several ways including anemia, dermatosis, paralysis and infections. Ticks transmit viruses, bacteria, protozoa, filaria, richettsias and spirochettes.
 

Mites
Follicle mites of humans live in hair follicles or sebaceous glands of the face. The incidence of these parasites is very high in the eldery but can be seen in young adults as well. Infection is usually benign but follicle mites have been suspected in the causation of some acne by introducing bacteria into the follicles. The dog follicle mite causes mange which can be seriously pathogenic and even lethal. The skin develops reddish pimples, becoming hot and thickened with an obnoxious exudate. Treatment can be difficult and sometimes infected puppies must be killed. In adult dogs treatment is usually successful and sometimes acquired immunity results in a decrease in symptoms and even no further signs of disease.

Scabies or sarcoptic mange results from infestation by the itch mite. The females burrow rapidly into the skin after mating and lay eggs in tunnels within the epidermis of the skin for about 2 months. Eggs hatch and make their way to the surface of the skin. The tunneling and secretions of the mites cause severe itching in infected persons. Transmission occurs usually by physical contact between infected persons.

Chiggers and dust mites also belong to this group of insects. Chiggers can cause an ithcy rash on the skin. Dust mite allergies are caused when mites, parts of mites or their excrement are inhaled by sensitive persons.

 

  

Parasitic Insects
 

Parasitic insects are very important ecologically, medically and economically. A broad definition of parasitic that includes mosquitoes and biting flies would make some 15% of insects parasitic.


Lice
Lice have been a part of human history as parasites without socioeconomic boundries. Archaeologists have even found traces of lice on mummies. These insects are wingless, flattened and have reduced or no eyes. The eggs (nits) are glued to the feathers or hairs of the host and there are three immature forms from egg to adult. There are no free living stages and they die when separated from the host.

Bed bugs
Bugs of the Family Cimicidae are reddish brown, dosoventrally flattened bugs that are rather large (up to 8 mm long) with no wings. They are nocturnal feeders that run very fast. They generally are most active around dawn when they feed on resting hosts. Daytime hiding places include mattress seams or crack in walls or furniture. The bites may cause allergic reactions in some people but generally cause little reaction. Domestic cleanliness and residual insecticides to hiding places is effective in controlling bed bugs.


Reduvid Bugs
These bugs are vectors for Trypanosoma cruzi. These are large winged bugs that live in cracks and crevices of poorly constructed homes or in thatched roofs. They are not picky about the source of their blood meal and will feed on whatever is available in the habitat. Improvements in construction methods, the use of metal rather than thatched roofs and residual insecticides are effective control measures.


Fleas
Of the some 2,000 flea species, most are parasites of mammals. Historically fleas have had a great impact as transmitters of the bacteria (Yersinia pestis) that causes the plague. Fleas are bilaterally flattened, commonly reddish black, and wingless. The adults feed by sucking blood from the host. The larvae feed on debris and flea droppings on the bedding. Fleas are amazing jumpers. For example, common fleas can jump some 33 cm high. The oriental rat flea can jump more than 100 times its body length.

Fleas are not host specific but have preferred hosts. Pulex irritans is the human flea but can be found on dogs, cats, squirrels, pigs, and others. This species can transmit the plague. Ctenocephalides canis and C. felis are the common dog and cat fleas, respectively. Controlling pet parasites can be accomplished by numerous commercially available residual, topical and systemic insecticides.


Flies (Order Diptera) represent the most medically important group of insects. They cause directly or indirectly a million human deaths each year. Some flies do not kill but contribute to disfiguring, debillitating diseases of many kinds either as vectors of pathogenic organisms or as parasites.

Black Flies
Black flies belong to the family Simuliidae and are found worldwide where the females feed on blood as well as plant nectar. Black flies are the vectors of Onchocerca volvulus. Mating occurs in flight, larval development occurs in running water and the flies are therefore numerous near rivers and streams. In the US and Canada, S. venustum are well known to fishermen and campers. Bites may produce little reaction in some people, but often small red itching wheals develop as a local reaction. Sometimes black fly fever can result which is characterized by nausea, headache, fever and swollen limbs.


Sand flies
Most sand flies do not affect humans, but rather parasitize reptiles and amphibians. However, some do feed on birds and mammals, including humans. Females take a blood meal in addition to plant fluids. Males eat only plant juices. Most are night time feeders due to the need to avoid hot desiccating environments. They are good vectors of disease and participate in leismaniasis, bartonellosis and some viral diseases.


Biting midges (no-see-ums)
These very small flies (less than 1 mm) are mostly daytime feeders that are most obnoxious on calm days as winds easily carry them away. Only females feed on blood. They act as vectors for various protozoal and viral disease of domestic animals.


Mosqutoes
Some 300 species of mosquitoes have been described with at least 150 of these being in N. America. The life cycle of mosquitos requires water for the larval and pupal stages. Adult females can live for 4-5 months but during the height of the summer season they may only live a couple weeks. Males may live only for weeks to a month. Species of mosquito transmit western equine encephalitis, St. Louis encephalitis, filarial worms, yellow fever, dengue fever, eastern encephalitis and malaria.


Tsetse flies
These flies of the Glossina species are found in Africa where they are vectors of sleeping sickenss. They are daytme feeders that are visually attracted to moving objects. Both sexes feed exclusively on blood, including that of humans.


Ticks
These epidermal parasites are found in nearly every country in the world. Their importance as agents and vectors of disease has long been recognized. Pathogenesis appears in several ways including anemia, dermatosis, paralysis and infections. Ticks transmit viruses, bacteria, protozoa, filaria, richettsias and spirochettes.
 

Mites
Follicle mites of humans live in hair follicles or sebaceous glands of the face. The incidence of these parasites is very high in the eldery but can be seen in young adults as well. Infection is usually benign but follicle mites have been suspected in the causation of some acne by introducing bacteria into the follicles. The dog follicle mite causes mange which can be seriously pathogenic and even lethal. The skin develops reddish pimples, becoming hot and thickened with an obnoxious exudate. Treatment can be difficult and sometimes infected puppies must be killed. In adult dogs treatment is usually successful and sometimes acquired immunity results in a decrease in symptoms and even no further signs of disease.

Scabies or sarcoptic mange results from infestation by the itch mite. The females burrow rapidly into the skin after mating and lay eggs in tunnels within the epidermis of the skin for about 2 months. Eggs hatch and make their way to the surface of the skin. The tunneling and secretions of the mites cause severe itching in infected persons. Transmission occurs usually by physical contact between infected persons.

Chiggers and dust mites also belong to this group of insects. Chiggers can cause an ithcy rash on the skin. Dust mite allergies are caused when mites, parts of mites or their excrement are inhaled by sensitive persons.