Friday, July 27, 2018

Ticks and mites: The differences we must know

Ticks and mites, like the fleas, bedbugs and lice are arthropods, the largest animal group. But, the similarity ends here. Fleas, bedbugs and lice are insects (Insecta group), while ticks and mites are arachnids (Arachnida group), which also includes spiders.

·         The most noticeable difference between ticks and mites is their size. Ticks are usually 1 mm long and can be seen with the naked eye. They can increase in length up to 3 centimeters after feeding. Mites, on the other hand, are less than one mm in size and hence, they cannot be seen with the naked eye i.e. they are microscopic. Ticks are usually acquired when walking through tall grass, shrubs and bushes.

·         Another important structural difference between the two lies in the hypostome, by which they attach to their hosts to feed. The hypostome in ticks is barbed and is inserted into the host allowing it to attach itself very effectively to the host. This is why it is difficult to remove a tick, especially when it is feeding as the hypostome may remain inside the host body. The hypostome in mites has no barbs and so mites can be easily be removed from their hosts.

·         Ticks have no hair on their bodies or have short hair, while mites have long hair on their bodies.

·         Ticks strictly live on animal hosts, while mites can feed on plants and animals.

Ticks and mites are external parasites of humans and are of public health importance as they are important vectors of diseases in humans (zoonoses).

Unlike ticks and mites, bedbugs, head lice and crab lice do not carry disease, though the bites caused by them can be bothersome. Only the body louse transmits infections to humans (Trench fever, epidemic typhus).

Rickettsiae (coccobacilli) and rickettsia-like bacteria are primary parasites of arthropods like lice, fleas, ticks and mites and usually spread to humans through the bites of ticks, mites, fleas, or lice that have previously fed on an infected animal.

Humans are accidental hosts in a chain of transmission between mites, ticks or fleas and animals (most commonly rodents).

·         Tick-borne illnesses include Lyme disease, Kyasanur forest diseases, Indian tick typhus, Rocky Mountain spotted fever, relapsing fever, tularemia, babesiosis, Q fever.
·         Scrub typhus and Rickettsial pox are mite-borne.

Rickettsial diseases are becoming common in India as a cause of acute febrile illness and are considered as emerging and re-emerging diseases. They are classically categorized into two: Typhus group and spotted fever group.

·         The Typhus group includes Epidemic typhus (louse), Murine typhus (flea) and Scrub typhus (mite).
·         The Spotted fever group includes Indian tick typhus (tick), Rocky Mountain spotted fever (tick) and Rickettsial pox (mite).

Then, there is another group of Rickettsial diseases, which includes Q fever and Trench fever.

The most commonly reported rickettsial diseases in India are scrub typhus (mite), murine typhus (flea), Indian tick typhus (louse) and Q fever (tick).

Other tick-borne diseases such as Kyasanur forest disease, Crimean Congo Hemorrhagic fever (CCHF), relapsing fever, Lyme disease and Q fever have also been reported in India.

Dr KK Aggarwal
Padma Shri Awardee
Vice President CMAAO
Group Editor-in-Chief IJCP Publications
President Heart Care Foundation of India
Immediate Past National President IMA

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