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Arthropods of Medical Significance

This page is still under construction and/or in the process of renovation. 

Introduction:

Arthropods (joint legged invertebrates) present in the environment may influence human health directly in a number of ways. 
    They may cause nuisance or injury directly - through their bites usually, which may result in inflammation or in toxic effects. 

    Constituents of their bodies (or their excreta) may behave as antigens, and result in allergic disease. 

    They may act as vectors of infectious disease

As far as human health is concerned, the two most important classes of arthropods are the insects (six-legged adults), and the arachnids (eight-legged adults). Of course, besides direct effects on human health, one must not lose sight of the economic consequences of infestation by certain arthropods -especially the effects of insects on crops.
 

Fleas 

Lice 

Locusts

Mites

Ticks
 

Insects

Fleas

The rat flea used to be an important vector of the plague. Although fortunately this is no longer a problem in most parts of the world, the disease has not been eradicated. 

A slide of a dog flea is shown on the right. Fleas of one species, typically hosted by a particular mammalian species (e.g. dog or cat) can also afflict members of another species (i.e. man).
Dog flea

Lice

These parasites are much more fussy than fleas, and lice afflicting one particular mammalian species are not at all likely to transfer to another mammalian species. Indeed, even within man, different types of the human louse lice infest different parts of the body. Thus the pubic (crab louse) lives in an envirnment which is less densely packed with hair than the head louse. 

Two pictures, of  human lice are shown on the right hand side.
Human louseHuman lice

Locusts:

These insects are most important to man as a species, because of their potential to wreak havoc on crops. 

However, a less known hazard is the potential for sensitisation (usually of laboratory workers) to antigenic constituents of the body of the insect. This can result in occupational asthma.
 

Other Arthropods

Mites

Scabies is caused by infestation with a parasitic mite (Sarcoptes or Acarus scabiei) that burrows under the skin, and which may result in severe itch especially by night. 

House Dust Mites (commonly Dermatophagoides pteronyssinus) can be important respiratory sensitisers and thus contribute to asthma morbidity. The antigenic component is present in the faeces of house dust mites. 

Moreover, mites can cause problems in a wide range of occupational contexts ranging from the making of cheese to the cultivation of plants, to the extraction of pharmaceuticals. 

Many species of mites can cause inflammation through allergy or in other ways. 

Images of two dust mites appear below.
House Dust MiteHouse Dust Mite

Mites are very widespread and probably under- recognised as occupational hazards. In conducting investigations, a very simple and easy test is to apply a piece of sticky adhesive tape to an area of presumed high infestation, and then sticking it down on glass slides, and examining the slides under low magnification with a microscope. 

If this fails, dust might need to be collected, and the mite population concentrated using a density gradient method (but in an occupational context when people are complaining of lots of symptoms, 
this added step is usually not necessary, as patient examination of only a few slides should reveal the mites). 

It is usually easy to determine that mites are present in large quantities using simple methods, but then one usually has to consult an acarologist to get a proper identification, since this can be a highly demanding task requiring specialist skills.

Ticks

under revision