American Dog Tick (Dermacentor variabilis)

americandogtick

All ticks are parasitic, feeding on the blood of mammals, birds, and reptiles. Ticks are the most important vectors of disease to domestic animals and second only to mosquitoes as vectors of disease to humans. Certain ticks inject venom while feeding on their hosts that produces a paralysis which can be fatal if the tick is not removed.

Ticks in North America are classified into two families, the soft ticks or Argasidae and the hard ticks or Ixodidae. Soft ticks lack a scutum or hard dorsal plate, are soft bodied, and the mouthparts are ventral and can not be seen from above. The soft ticks are mainly nocturnal, feeding rapidly during the night and concealing themselves during the day in cracks near the nest of their host. The female soft tick indulges in several blood meals and generally lays small batches of eggs after each feeding until 100 to 200 total eggs are laid. The eggs develop into nymphs which may molt several times before reaching the adult stage. Different species of soft tick can be found in poultry houses, inside the ears of rabbits and in bat caves or rodent burrows. An important pest of poultry, the Fowl tick Argas persicus, attacks sleeping birds at night. This flattened tick is well adapted to conceal itself in the woodwork of buildings during the day.

Identification

The hard ticks are more commonly known to the general public, especially those ticks that transmit human disease. Hard ticks have a hard dorsal plate called the scutum, and the mouthparts protrude and can be seen from above.

Biology

These ticks, after settling on their hosts, essentially turn into an automatic pump extracting blood for nourishment. After finishing her final blood meal, the engorged female hard tick drops off the host animal and can lay from 2,000 to 18,000 eggs on the ground. The first stage to hatch from the egg is called a larva. The larvae have three pairs of legs, are active and generally attach to small animals. After they feed and drop off, they molt to become a first instar nymph. In hard ticks, there is only a single nymphal stage. The nymphs have four pairs of legs; they also attach to an animal, engorge, drop off and molt to become adults. Hard ticks may have one, two or three different host animals.

The first tick recognized as a vector for human disease was the wood tick Dermacentor andersoni, which was shown early in this century to be the causative agent of Rocky Mountain spotted fever. This pathogen–a small, gram-negative intracellular coccobacillus belongs to the family Rickettsiaceae (R. rickettsii). Rocky Mountain spotted fever has now spread from the Rockies to the south central, southern, and eastern regions of the US, where the disease is associated with the dog tick D. variablis. About 1000 cases of Rocky Mountain spotted fever are reported annually, and new foci of infection are continually being identified. Dermacenter andersoni is also known for its ability to transmit Q fever, tick paralysis, tularemia and Colorado tick fever. Rocky Mountain spotted fever has a high mortality rate in man when untreated.

A second tick-borne rickettsial disease that is increasing in frequency and distribution is ehrlichiosis. It is caused by gram-negative intracellular rickettsia of the Ehrlichia genus, primarily Ehrlichia chaffeensis. Ehrlichiosis is widely distributed and more common in many areas than Rocky Mountain spotted fever. Epidemiologic studies have turned up sporadic cases in south central, southern, and eastern states in a distribution similar to that of the Lone Star tick Amblyomma americanum. Recently cases of human granulocytic ehrlichiosis have been described in the northern US in areas where Lyme disease and babesiosis are endemic. Transmission by Ixodes scapularis or Dermacentor variabilis is suspected.

To Remove engorged ticks from animals or man

An engorged tick is hard to remove after it has become attached. Its head is partially hidden by its enormously enlarged abdomen and its mouth parts are well attached into the skin. The following procedure will help you to remove these ticks quickly and safely. The best method is to grasp the tick with fine tweezers, as near the skin as you can, and gently pull straight out. Since the Lyme bacteria and other diseases are injected by the tick when it bites, you must be careful not to squeeze the tick when removing it which could result in more bacteria being injected. Do NOT attempt to remove with lighted cigarettes, matches, nail polish, or Vaseline. Save the tick in case of illness so that a more accurate diagnosis can be made. Dogs can catch Lyme disease from ticks and will need to be treated by a Veterinarian.

Avoiding tick bites

Do not let the fear of ticks prevent you from enjoying the warmer months of the year. If you are in a tick infested area you should be wearing long, light colored pants tucked into your socks. This will help you to spot ticks before they become attached. Ticks rest in brushy vegetation waiting for an animal to pass by; they are not found as often in open areas. A careful check for ticks after a day of outside activity will help to prevent tick disease since ticks must remain attached for many hours before the disease organism is transmitted.

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