Practical Parasitology

Introduction to the Hard Bodied Ticks and Lyme Disease


Overview

Ticks are divided into two groups hard bodied and soft bodied . Common hard bodied ticks will be studied here. This section is by no means the definitive source for identification it is a guide only. There are many genera and species of ticks some are Lyme disease transmitters and some are not. Examples of the genera Dermacentor, Ixodes and Rhipicephalus will be outlined in this section.

The etiological agent for Lyme disease is the spirochete Borrelia burgdorferi.(46), (47), (48), (49), (50), (51), (52) A rash may develop a short time after an infected tick bites. The bite may have the characteristic bulls eye appearance. Flu like symptoms and joint pain may also occur. Chronic infection, weeks to months after infection may result in facial palsy, joint pain and severe head aches. Early treatment is more successful.(49)


Anatomy of the Tick

Click on the images below to enlarge.

Tick ventral Tick dorsal Tick capitulum Typical capitulum of hard bodied tick Typical hypostome of hard bodied tick

The 3 main body parts of the tick are the body, scutum and the capitulum. The capitulum of a soft bodied tick is concealed by the scutum. It is the hypostome that is inserted into the flesh of a warm blooded animal. Each genera has differentiating characteristics such as the shape of the scutum, bifid coxa 1, internal or external spurs, festoons and the shape or direction of the anal groove to mention a few.


Genus Dermacentor

Dermacentor species Egg laying D. variabilis - American Dog Tick D. variabilis male D. variabilis male D. variabilis female D. variabilis female D. variabilis female

Dermacentor species ticks are ornate, with eyes, festoons, anal groove posterior to the anus and with bifid coxa 1. The schematic diagram and the photographs of D. variabilis illustrate the Dermacentor species. D. variabilis is a vector of Rocky Mountain Spotted Fever and Tularaemia. It does not transmit Lyme disease.


Genus Ixodes

Ixodes species I. ricinis I. ricinis I. scapularis I. scapularis I. cookei male I. cookei male I. cookei female I. cookei female

Ixodes species ticks are inornate, do not possess eyes and with an anal groove surrounding the anus anteriorly. The Ixodes of Canada contain approximately 20 species. It is important to note when identifying ticks to know where the tick came from. Because of the diversity in this field a tick from Europe may resemble one from North America. A good example of this is Ixodes scapularis a Lyme disease transmitter in North America and the European tick Ixodes ricinis. Also a Lyme disease transmitter. Please note that the palpi are missing in the photograph of I. ricinis. The illustrated I. cookei although not a Lyme disease transmitter is a vector of Powassan Encephalitis virus.


Genus Rhipicephalus

Rhipicephalus species Rhipicephalus sanguineus Rhipicephalus sanguineus

R. sanguineus is said to be the most common tick in the world.(53) This tick has very prominent eyes and an anal groove posterior to the anus with a median groove posterior to that.


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