1. Ticks Paul R Earl Facultad de Ciencias Biológicas Universidad Autónoma de Nuevo León San Nicolás, NL, Mexico

2. TICKS are universaly distributed ectoparasites of vertebrates that take blood and lymph from them. They are related to mites and distantly to spiders. They are vectors of many microbial pathogens. About 850 species have been described, and the most important in Europe, the Far East and the New World are Ixodes species Try The Ticks of the World (Acarida, Ixodida). Nomenclature, Described stages, Hosts, Distribution (Including new species described before 1/01/96) by JL Camicas, JP Hervy, F. Adam, PC Morel. Ed Orstom, Paris, 1998.

3. Ixodes ticks transmit the spirochete Borrelia burgdorferi of Lyme disease in Eurasia and North America, tick-borne encephalitis virus (TBEV) in Europe and Asia, human babesiosis, caused by Babesia microti and B. bovis to man in North America, Babesia divergens in Europe and B. bigemina & B. bovis in Mexico. Human granulocytic ehrlichiosis (HGE) now called human anaplasmosis is caused by Anaplasma phagocytophila, A. equi & HGE agent in North America and Europe. The pathogens Bartonella spp., Francisella tularensis, Coxiella burnetii and Rickettsia spp. cause tularaemia, Q-fever and tick-borne lymphadenopathy (TIBOLA) are importance.
Besides TBEV and B. burgdorferi, 5 additional virus species (Eyach-, Erve-, Tribec-, Lipovnik-, Uukuniemivirus) have been isolated from ticks in Germany alone. In addition, 4 species of bacteria (Rickettsia slovaca, C. burnetii, A. phagocytophila, Ehrlichia or ! Anaplasma canis) and 4 species of protozoa (B. divergens, B. bigemina, B. bovis, B. microti) are known to cause infections even though sometimes silent ones by the production of antibodies. Infections in humans caused by the Louping ill virus after tick bite are extremely rare. Louping ill virus is a disease of sheep mainly and transmitted by Ixodes ricinus.

4. Tick biology Ticks are arachnids that comprise 2 major families: the Ixodidae (ixodid or hard ticks), having a dorsal shield (scutum), and the Argasidae (argasid or soft ticks). These 2 general taxonomic categories differ in form, behavior, pattern of development, and disease relationship. Ixodes ricinus is equipped with long cheliceras and the central hypopharynx: the piercing and sucking mouthparts. The hypostome is equipped with recurved spines. A quick hardening cement in ticks can improve the functioning of the puncture channel.
The order Acarina of the class Arachnida contains mites and ticks. Spiders are of course related. Members of Acarina differ from other arachnids in that the body is not segmented. The cephalothorax and abdomen are combined into one body region. Larval mites and ticks have 3 pairs of legs, whereas nymphs and adults have 4 pairs. Mites inhabit most environments from deserts to rain forests, mountain tops to tundra, and from ocean floors to lakes. The relatively few species parasitic on humans, sometimes causing dermatitis followed by allergic reactions.

5. TICKS rank second to mosquitoes as disease transmissors and disperse a greater variety of pathogens. Persistent painless blood-sucking of large amounts of blood like 8 ml over weeks on mammals and birds allows wide dispersion. Wide host range and tendency to feed on several hosts during their lifetime ensures ample opportunity to acquire and transmit pathogens. Hardiness and longevity allow them to survive periods of unfavorable conditions while waiting for a host. Waiting is called questing. High reproductive potential ensures large populations and a high frequency of host-vector contact. Ticks feed slowly. This allows for pathogen acquisition and transmission, and vector dispersal by host migration.
Saliva has a bloodmeal anticoagulant and also local anesthetics so the tick bite is effective and painless, often remaining unnoticed by the host. On humans, ticks prefer to attach themselves to the hair-covered portion of the head, to the arm and knee bends, hand, feet and ears as well as the gluteal and genital regions. In children, most ticks are founs on the head.

6. With 3-host ticks, the larva, nymph and adult each feed on a different individual vertebrate host, often a wide range of species, for a period of a few days. Hard ticks moult only twice; the egg stage generates a 6-legged larva, which develops into an 8-legged nymph, which in turn moults to produce a similar but larger adult. Hard ixodid ticks increase their body mass 10–200 times during feeding. Larvas feed on their host for an average of 2–4 days and increase their mass 10–20 times. Nymphs feed 3–5 days and increase by 15–40 times and adult females feed 6–10 days and increase by 100–200 times.
All tick stages feed only once per stage, with the exception of the adult male, which can feed several times or not at all. It increases its body mass only by 2. Copulation usually takes place on a host before blood feeding shortly after which the male dies. A few weeks later, the female lays between 1000 and 5000 eggs.

7. Each stage of I. ricinus takes about 1 year to develop from one to the next, so the shortest life cycle takes 3 years to complete. However, it may vary from 2-6 years depending on the availability of hosts and climatic conditions. I. ricinus spends 99% of its life living free in certain locations with special vegetation. Ticks digest their blood meals intracellularly. Ticks do not pierce blood vessels and are pool-feeders. They feed on lymph and dissolved cells besides blood.
The acquisition and transmission of pathogens are separated by long periods of free living. A series of hormonally mediated changes occur in the body of the feeding tick during the first day of host contact; The tick is blind, but senses carbon dioxide, temperature, odors, ammonia and movements. The Haller’s organ on the final segment of the first pair of legs, serves for orientation during feeding.
Questing ? The tick is waiting on vegetation for a host. Flagging ? A flag of say 1 square m of cloth on a stick is dragged. Ticks jump on the flag from which they can be collected. Traps can have dry ice as an attractant.

8. Hard ticks (family Ixodidae) are responsible for transmission of the majority of tick-borne diseases of humans. They are the vectors of babesiosis, Colorado tick fever, Lyme disease, Rocky Mountain spotted fever, and tularemia in the US. While soft ticks (family Argasidae) do not directly transmit these diseases to man, they may be involved in the maintenance of natural cycles among reservoir hosts, as in the case of Colorado tick fever. In addition, soft ticks of the genus Ornithodoros are the vectors of tick-borne relapsing fever.
Hard ticks have a hard upper surface called a shield or scutellum that covers the entire back of the male, but only partly covers the female. Mouthparts are visible from above. They attach securely and may feed for weeks, using a different host in each life stage. The female produces as many as eggs.
Soft ticks do not possess a shield, so the sexes look alike. Their mouthparts are beneath the anterior end of the body and are not visible from above. Principal hosts are birds, domestic animals, bats and small mammals. These ticks feed intermittently at night. The female oviposits following the blood meal and produces 500 to 1000 eggs during her lifetime.

9. Developmental Stages Seed tick
Developmental Stages Seed tick. Normally, thousands of tiny larvas hatch from the eggs batch and crawl about searching for a host. Lucky ones attach to a mammal or lizard. Feeding time is generally short, a few hours or a day, but up to 3 days for Ixodes scapularis. During feeding the host wanders and the tick is transported to a new location where it drops off when engorged. Nymph. After molting, hard tick nymphs climb grass leaves or plant stems and quest. As they become higher in ground level, they tend to attach to larger hosts. Soft tick nymphs burrow in and await the arrival of a host. After several days of feeding they drop off and again molt.

10. Adult. Ticks sometimes wait for months or more than a year for a suitable host. When finally engorged, they drop off to oviposit. Ticks that tend to feed on the same host species at each stage are referred to as 1-host ticks, whereas those that feed on different hosts each time are called 3-host ticks. The first pair of legs is extended and used to grasp the host when contact is made. This behavior is known as questing. If warmth or carbon dioxide is detected by the tick, it will seek it out and climb onto the host as it passes. The height at which questing takes place determines the size of the host and therefore, to some extent, the species selected.
There is considerable variation between species, and the different life stages of some species, in the height at which they quest.
Many soft ticks, in contrast, inhabit caves, dens, stables, and other places used by potential hosts. They typically secrete themselves in loose soil or cracks and crevices by day and attack their host at night, usually while it is asleep. They crawl to the host, engorge in a few minutes or hours, and return to their hiding place.
All ticks orient to potential hosts in response to products of respiration. Carbon dioxide, in particular, is attractive at a distance. This characteristic is helpful in surveillance studies because many species can be collected using traps baited with dry ice.
When feeding, the tick uses its cheliceras (teeth) to cut the victim's skin and then inserts its mouth parts. The hypostome (feeding tube) has many rows of recurved barbs that become cemented in
and anchor the tick to its host, making it very hard to withdraw by pulling on the tick. Blood is pumped by a muscular pharynx and the salivary glands produce an anticoagulant that allows long periods of feeding without the host blood coagulating. The tick usually moves to the highest part of the host to attach and feed on the head or ears.

11. The occurrence of tick-borne encephalitis viruses is determined by the distribution of their tick vectors which, in turn, is governed by ecological conditions. The tick hosts and vectors of TBE group viruses are primarily of the genus Ixodes. In central Europe I. ricinus is the main transmitter of the Western virus subtype. I. ricinus activity starts when the temperatures rises to 5–7 C in March or April and ends late in the year in October and November.

12. American dog tick (Dermacentor variabilis)
The American dog tick, a 3-host tick, is widely distributed east of the Rocky Mountains and along the Pacific coast. Dogs are the preferred host. They feed on many large mammals including man. This tick transmits the causative pathogen of Rocky Mountain spotted fever and possibly Q fever to humans. Q stands for Queensland. The adult stage is identified by ornate markings on the scutum. Also, they have 11 festoons, simple eyes and short mouthparts.
American dog ticks prefer overgrown empty lots and the like, fields, and edges of paths and trails. They wait on grass (questing) and weeds for a suitable host to brush against the vegetation.
Larval activity begins in early spring when they feed on rodents such as meadow voles and whitefooted mice, whereas the 8-legged nymphs may be found on whitefooted mice, cotton rats and rabbits during winter months.
The female feeds, mates, becomes engorged and drops off to lay 1,000-3,000 eggs. The life cycle requires from 4 months to over a year.
A ventral view
Male

13. Brown dog tick (Rhipicephalus sanguineus)
The brown dog tick when it infests domestic pets is often established inside houses. It is the most widely distributed tick in the US. It does not transmit human diseases. A parasite of dogs, it attaches to the ears and in between the toes of dogs. The engorged female ticks, sometimes are particularly noticeable as they crawl on walls.
The entire life cycle can be completed in less than 2 months. Homes and yards can become heavily infested. This tick does not survive outside in northern winter.
Why don’t you buy an insecticide collar for your dog ?

14. Rocky Mountain wood tick (Dermacentor andersoni)
It is the major vector of Rocky Mountain spotted fever, a rickettsial disease of man. It is common in the Rocky Mountain states and in southwestern Canada, where it is a vector of bovine anaplasmosis and canine babesiosis (blood parasites of animals). The toxins injected as it feeds cause tick paralysis in humans as well as animals.
This tick mates during feeding, after which the female detaches from the host and deposits several thousand eggs over a period of a month. Hatched seed ticks attach to small rodents, feed, detach and
develop into the nymphal stage. Nymphs seek shelter and are inactive until the following spring, when they attach to another animal, feed, drop off and molt into the adult stage. The adult stage overwinters and the following spring they attach to a large animal, feed and start the life cycle over. This requires 3 to 4 years.

15. Lone star tick (Amblyomma americanum)
The lone star tick is found in the southeastern sector of the US, but reaches as far north as New Jersey. Due to its long mouth parts, the bite is painful. It is a vector of human anaplasmosis (ehrlichiosis), tickborne typhus and tularemia. Females of this species are easily recognized by the conspicuous silvery-white spot on the back or scutum. The male tick has horseshoe shaped markings on the posterior region of its reddish-brown body.

16. Common hosts for all life stages are livestock, dogs, deer, birds and humans. This tick, like many other species, is attracted by the scent of animals, hence is numerous along roads, paths and trails. Female ticks that drop from animals along bedding areas, pathways and trails further increase the concentration at these sites.

17. Deer tick (Ixodes scapularis)
The deer tick or black legged tick inhabits the eastern 2/3rds of the US, and its close relative, Ixodes pacificus, is found on the west coast. These ticks are the main vectors of Lyme disease, human anaplasmosis and babesiosis. Lyme disease signs and symptoms include a ring-shaped rash at the point of the bite, which usually appears within a few days to a month after the bite. They prefer wooded areas, feeding on a wide variety of birds, mice, deer, domestic animals and man. They are a 3-host tick, the adult reaching only the size of a sesame seed.

18. Ixodes pacificus
Overwintering adults produce eggs in the Spring and the larvae feed primarily on white-footed and other mice during the summer. They molt into nymphs the following Spring and feed on larger animals in the woods and grasslands. This is the primary stage that transmits the Lyme disease pathogen to man, following a feeding period of 48 hours or more. Adults feed on deer and other larger mammals.

19. Boophilus microphilus
Boophilus microphilus is a crucially important worldwide transmittor of cattle disease like anaplasmosis and babesiosis.
An engorged female of B. microphilus >

20. Relapsing fever ticks (Ornithodorus spp.)
This is the most important genus of soft ticks from a medical standpoint. Relapsing fever ticks are seldom seen by the average person since they are nest ticks and can survive starvation for months or even years. Persons bitten may contract relapsing fever.

21. Fowl tick (Argas persicus) This soft tick feeds rapidly at night and subsequently oviposits in cracks and crevices. The tick has two or three nymphal stages before molting to the adult stage. Like the relapsing fever tick, these ticks may live for months or years without a blood meal. Argus persicus readily attacks humans but does not transmit human disease. It is a vector of fowl spirochetosis.

22. Ixodes ricinus I. ricinus is the most important vector in Europe.
Ixodes ricinus carries louping ill to sheep and MANY other diseases.
I. ricinus is the most important vector in Europe.

23. Spinose ear tick (Otobius megnini)
This soft tick gets its name from the habit of larvas and nymphs to infest the ears of cattle, horses, mules, etc. and occasionally people. This is a 1-host tick. All stages feed on the same host.

24. Summary In this introductory lecture, most fundamental points are reviewed, and some economically important ticks are illustrated. How ticks, mites and mosquitoes fit into temperate and tropical medicine and veterinary practice is a very long story involving discovery not told here Who was Howard Taylor Ricketts ? The information here on ticks is a good start for vector control or other fields of interest that are often neglected. All ticks are parasites! Modern medicine or its US version does not concentrate on vector transmitted diseases which are at once tropical and rural, and once upon a time were colonial.
Progress in sanitation and urbanization have allowed attention to turn to health objectives belonging to cardiology, cancer studies and so forth that are far from the infectious diseases of the rural poor, most of whom live in the tropics.