MITES

INTRODUCTION

• Mites, along with ticks, are small arthropods belonging to the subclass Acari (also known as Acarina) and the class Arachnida. 
• The scientific discipline devoted to the study of ticks and mites is called acarology.
• In soil ecosystems, mites are favored by high organic matter content and by moist conditions, wherein they actively engage in the fragmentation and mixing of organic matter.

MOST COMMON SPIDER MITES

SCIENTIFIC CLASSIFICATION

Kingdom: Animalia

Phylum: Arthropoda

Subphylum: Chelicerata

Class: Arachnida

Subclass: Acari

Leach, 1817

Superorders

Acariformes

Parasitiformes

LIFE CYCLE

SYMPTOMS

DIVERSITY AND ECOLOGY

• Mites are among the most diverse and successful of all the invertebrate groups. 
• They have exploited an incredible array of habitats, and because of their small size (most are microscopic), go largely unnoticed. 
• Many live freely in the soil or water, but there are also a large number of species that live as parasites on plants, animals, and some that feed on mold.
• It is estimated that 48,200 species of mites have been described.
• Mites occupy a wide range of ecological niches. 
• For example, Oribatid mites are important decomposers and occur in many habitats. 
• They eat a wide variety of material including living and dead plant and fungal material, lichens and carrion; some are even predatory, though no species of Oribatida mite are parasites. 
• Many mites which have been well studied are parasitic on plants and animals. 
• One family of mites Pyroglyphidae, or nest mites, live primarily in the nests of birds and animals. 
• These mites are largely parasitic and consume blood, skin and keratin. 
• Dust mites, which feed mostly on dead skin and hair shed from humans instead of consuming them from the organism directly, evolved from these parasitic ancestors.
• Insects may also be infested by parasitic mites. 
• Examples are Varroa destructor, which attaches to the body of the honeybee, and Acarapis woodi (family Tarsonemidae), which lives in the tracheae of honey bees. 
• There are hundreds of species of mites associated with other bee species, and most are poorly described and understood. 
• Some are thought to be parasites, while others beneficial symbionts. 
• Mites also parasitize some ant species, such as Eciton burchellii.
• Some of the plant pests include the so-called spider mites (family Tetranychidae), thread-footed mites (family Tarsonemidae), and the gall mites (family Eriophyidae). 
• Among the species that attack animals are members of the sarcoptic mange mites (family Sarcoptidae), which burrow under the skin. 
• Demodex mites (family Demodicidae) are parasites that live in or near the hair follicles of mammals, including humans. 
• Acari are mites, except for the three families of ticks.
• The tropical species Archegozetes longisetosus is one of the strongest animals in the world, relative to its mass (100 μg): It lifts up to 1,182 times its own weight, over five times more than would be expected of such a minute animal.
• Mites also hold the record speed; for its length, Paratarsotomus macropalpis is the fastest animal on Earth.

MEDICAL SIGNIFICANCE

• The majority of mite species are harmless to humans, but a few species of mites can colonize humans directly, act as vectors for disease transmission, or cause or contribute to allergenic diseases.
• Mites which colonize human skin are the cause of several types of skin itchy rashes, such as grain itch, grocer's itch, and scabies. 
• Sarcoptes scabiei is a parasitic mite responsible for scabies which is one of the three most common skin disorders in children.
• Demodex mites, which are common cause of mange in dogs and other domesticated animals, have also been implicated in the human skin disease rosacea, although the mechanism by which demodex contributes to the disease is unclear. 
• Chiggers are known primarily for their itchy bite, but they can also spread disease in some limited circumstances, such as scrub typhus. 
• The house-mouse mite is the only known vector of the disease rickettsialpox. 
• Dust mites cause several forms of allergic diseases, including hay fever, asthma and eczema, and are known to aggravate atopic dermatitis.
• House dust mites are usually found in warm and humid locations, including beds. 
• It is thought that inhalation of mites during sleep exposes the human body to some antigens that eventually induce hypersensitivity reaction.

PREVENTION

• Prevention is preferable to having to control an outbreak. 
• This can be summed up as general hygiene and screening of all cultures and material coming into the laboratory and destroying or isolating ail infested material. 
• Even so, separate handling, storage and quarantine of fresh material is desirable, as slightly infested cultures can develop heavy infestation if undetected at first examination. 
• If it is necessary to handle infested material, the culture collection should be well isolated.

 CONTROL

Different workers have varying views on control. 

Some who are handling a quick turnover of infected material may not even regard a few mites as serious, but in a culture collection they spell disaster. 

A combination of prevention and action seems preferable. These can best be classed in several categories: 

1. Hygiene

Hygiene coupled with quarantine is perhaps the best protection.

• All work surfaces must be kept clean.
• Cultures should be protected from airborne contamination.
• Mites can be carried on workers' hands and clothing.
• Cramped laboratory conditions and crowded arrangement of cultures increase the risk of infestation.
• Work surfaces and benches should be washed regularly with acaricide. The acaricide is left for sufficient time to act (overnight) and washed off, preferably with alcohol. As some acaricides are toxic to man, protective gloves should be worn.

The acaricide used at the CMI is Actellic (ICI, Agrochemicals, PLC). 

Other acaricides available for agricultural and grain storage purposes are Murfit, Reldan and Dursban (Murphy Chemicals Ltd) and Satisfar (Sandoz Ltd

As mites appear to become resistant, the acaricide should be changed from time to time.

• Infected cultures should be removed immediately and sterilized if possible. All cultures in the immediate area should be checked and isolated.

2. Fumigation

• Cultures may be stored in cupboards or boxes with acaricides either as preventative or short-term treatment. Camphor and paradichlorbenzene (PDB) have been used for this, but are now regarded as toxic. PDB also has some effect on fungal growth. Drops of Kelthane and Crypo on culture plugs (Smith, 1967) were effective. Current safety practice would suggest that fumigation is no longer desirable.

3. Mechanical and chemical barriers

Many physical methods of prevention of infestation and spread have been tried.

• Cultures are placed on a platform or tray surrounded by water, oil, petroleum jelly or other sticky material. Handling of cultures becomes unpleasant and protection is only from crawling mites.
• Culture bottles or plates may be sealed, but it is necessary to allow growing cultures free respiration, so a means of sealing which is permeable to air is desirable.
• Snyder and Hansen (1946) sealed bottles below screw caps or above the cotton wool plugs (well pushed down) with sterile cigarette papers using copper sulphate glue (20 g gelatin, 2 g copper sulphate, 100 ml water). The pores of the paper allowed respiration but prevented movement of mites, thus protecting clean cultures and isolating infested ones. Care is necessary to ensure the seal is effective. 
• Smith (1971) recommends the use of disposable plastic bottles with plastic caps which, when screwed down, still allow respiration but exclude mites. 
• Smith (1978) described a screw-lid closure with a hole sealed with Metricel.
• Sealing Petri dishes and bottles with various modern plastic tapes often reduces spread but, by means of cracks or wrinkles, mites can eventually penetrate cultures stored for a long time. 
• Tight cotton wool plugs present a considerable barrier but are not completely effective, though a mite that has passed through cotton wool is often much cleaner. Some workers treat plugs with mercuric chloride solution. 
• This kills the mites but is poisonous and dangerous to handle even if a red dye is included to indicate its presence. It is also toxic to fungi.

4. Protected storage

Many methods used for long-term storage of cultures in culture collections prevent infestation.

• Mites do not infest cultures stored under mineral oil. 
• Cold storage at 4-8C greatly reduces movement of mites but does not kill them, so they continue to multiply when the cultures are removed from the refrigerator.
• Deep-freeze storage at approximately -20C usually kills any mites present. Storage in a deep freeze for three or four days can be used prior to cleaning to treat infested material that is too valuable to discard. 
• Freeze-dried ampoules are sealed and totally protected.
• Storage at ultra-low temperatures, for example in liquid nitrogen, gives total protection.
• Cultures stored in silica gel are in vials or bottles with screwed-down caps, so are totally sealed.

REFERENCES : MITES