No single tick can be considered the Lyme disease tick as there are a number of types that can be responsible for carrying and transmitting Lyme disease bacteria in different geographical areas. Getting to know the ticks present in the local area can however help people judge their risk of infection more accurately and increase awareness of Lyme disease. The size of a tick may also differ greatly depending on whether it is unfed or fully fed (engorged). Male and female ticks also vary in size and color within a tick species.
Ticks are closely related to insects but are actually a type of mite. The female blacklegged ticks found commonly in North America, particularly the western blacklegged tick in the Pacific Northwest, are around 3-5mm in length prior to feeding. These female ticks are red and dark brown in color and are usually larger than male ticks, growing up to the size of a grape after feeding in some cases. Unfed ticks are usually lighter in color and may be difficult to make out against the skin or fur. Ticks may be introduced to an area not considered to be endemic for Lyme disease by migratory birds or mammals but the risk of contracting Lyme disease is still quite low in such places.
The Tick Family
Ticks as a family are divided into two distinct groups, those considered soft ticks (Argasidae) and those hard ticks (Ixodidae). Hard ticks of the Ixodes genus are those which transmit Lyme disease infection although soft ticks transmit relapsing-fever Borrelia which can cause some confusion. Some relapsing-fever-like Borrelia such as B. myamotoi are also now thought to be transmitted by the same hard ticks that transmit Lyme disease bacteria. The presence of B. burgdorferi in ticks does not necessarily mean that they are capable of transmitting infection to new hosts however, and these bacteria have been found in mosquitoes and deer flies with no evidence of their ability to infect humans. The ticks which are considered important vectors for Lyme disease transmission are Ixodes persulcatus, I. ricinus, I. pacificus, and I. scapularis (dammini). Of these four the first two constitute the major problems in Europe, Russia, and Asia, whereas, the latter two are identified in North America. I. persulcatus is largely responsible for cases of Lyme disease in Asia and Russia, and I. ricinus for those cases seen in Europe. The distribution of ticks which cause Lyme disease in North America is also further delineated by a propensity for infection through the bite of I. pacificus on the west coast, and I. scapularis on the east coast where most cases are thought to occur.
The soft ticks have a pear or oval shape with a rounder body and mouthparts on the anterior ventral surface (at the front and slightly underneath, near the tick’s belly). The hard ticks are usually flattened when unfed and the mouthparts project more clearly anteriorly. Ixodes ticks also have a sclerotized (hardened) dorsal plate called the scutum on their backs which is frequently ornate but present throughout the tick lifecycle. However, visual differences are not the only kind to exist between the Lyme disease tick found in Europe, Asia, and Russia, and those in the US, as variations also occur in behaviour and disease transmission.
Continue Reading –> Which Tick Species Lives Where?