Insects and their relatives can affect our health and that of our livestock and pets in many ways-
Nuisance
e.g. bush flies, ants
Phobia
Spiders, cockroaches, moths
Biting, sucking
Ants, bed bugs, March flies, Horse flies, mosquitoes, sand flies, fleas
Venoms and allergies
Wasps, ants, bees, spiders, ticks, dust mites, cockroach faeces
Blistering, inflammation and urtication (irritating hairs)
Blister beetle, 'Spanish fly', caterpillars, spiders
Disease, infestation
Head, body and pubic lice, mites (scabies), Myiasis (fly strike), bot flies
Disease vectors
Whereby an insect or other arthropod does not cause actual disease but transports the organism responsible.
Two vector methods:
Protozoa - malaria, sleeping sickness, Chagas' disease, Leishmania
Arboviruses - myxomatosis, equine encephalitis, yellow fever, dengue, blue tongue virus
Rickettsias - endemic typhus, murine typhus, scub typhus
Bacteria - plague
Nematodes - elephantiasis (filariases), river blindness
Disease organism - protozoan
Vector - Mosquito (Dusk and night biting)
Hosts - Man
Distribution - Tropical Asia, Africa, South America, Pacific
Method -
DDT etc
Numbers affected
Control -
Disease organism - protozoan
Vector - Tse tse fly
Hosts - Man (preferred), cattle
Distribution - arid Africa
Method - The protozoan multiplies in the tse tse fly's blood and then migrates to the salivary glands from where they are transmitted to humans or cattle by biting. In humans, the protozoan multiplies in the blood (stage 1), then in the lymph nodes (stage 2). The disease can also enter the central nervous system. Death by toxins follows in a few months, preceded by emaciation and weakness/sleeping.
There is no cure.
Control -
Disease organism - protozoan
Vector - reduviid (assassin) bug
Hosts - Man, monkeys, armadillos, various mammals
Distribution - Dry marginal agricultural areas of South America
Method - The bug ingests infected blood of a mammal. The disease organism is deposited in the faeces of the bug onto the skin of the next host mammal. It enters the mammal's blood via the skin or eye, is engulfed by a host macrocyte and divides within it. It then circulates within the blood causing toxaemia. It may also lodge and multiple in soft tissues and organs (heart, brain, kidney) and cause either death or chronic illness.
Control -
Disease organism - protozoan
Vector - sandflies
Hosts - Man, dog, rat
Distribution - Generally arid areas in Africa, Middle East, South America,
Method - the disease organism multiples in the fly's midgut, migrates to the pharynx and after 3-5 days is ready for transmission to another mammal. In a mammal, the organism is engulfed by a phagocytic cell where it multiples again in several cycles
Injury is mostly minor but disfiguring, particularly for infants and infections on mucous membranes. It may also cause liver and spleen enlargement.
Control -
There is currently no content for plague.
Disease organism - nematode
Vector - a day-biting mosquito (Culex quinquefasciatus)
Host - Man
Distribution - Asia, PNG
Method - The worm develops to infective stage in the flight muscles of the mosquito, migrates to the head and completes development in the human host. The worm takes several months to maturity and can live in human blood for many years.
Injury - Currently 120 million people are affected, 40 million seriously.
The nematode damages lymph vessels, preventing proper drainage from limbs, breasts and genitalia, leading to massive swelling. There is no cure for the injury and preventative medicines available are useful only in presymptomatic stages.
Control - Standard mosquito control (see malaria) except for netting on beds
There is currently no content for river blindness.
Copyright © University of Sydney. Last updated February, 2004. Site construction and maintenance: SOBSTDU. Email us here with your comments and feedback.