Ixodes scapularis

Ixodes scapularis
Ixodes scapularis (female) the vector for Borrelia burgdorferi the causative agent of Lyme Disease, Babesia microti causative agent of human babesiosis, and Anaplasma phagocytophilum causative agent of human granulocytic ehrlichiosis.

Sunday, October 10, 2010

Ixodes scapularis as a vector


Ixodes scapularis is a known vector for a number of diseases including Lyme disease (caused by the bacteria Borrelia burgdorfer), human babesiosis (caused by the protazoan Babesia microti), and human granulocytic ehrlichiosis (caused by the bacteria Anaplasma phagocytophilum). The principal source (reservoir) of these pathogens is the white-footed mouse (Peromyscus leucopus). A larva can also pick up Borrelia burgdorferi from Tamias striatus (chipmunks) and some species of birds. Lyme’s disease is the most prevalent of these vector-borne diseases with over 100,000 cases reported in the United States since 1982. Lyme disease, also known as Lyme Borreliosis, has three phases. The first symptom of the disease is a rash that appears at the bite site. It is a red area that clears in the center as it expands to a final diameter of about 15 cm. This distinctive target-like rash only occurs in about 75% of the cases. Flulike symptoms appear a couple of weeks after the rash fades. Antibiotics taken during this interval are very effective in limiting the disease. During the second phase chronic neurological symptoms, such as facial paralysis, meningitis, and encephalitis may be seen. In addition the heart is often affected, causing an irregular heartbeat that can become so severe that a pacemaker is required. In the third phase patients may develop arthritis, and more severe chronic neurological symptoms. Although there are several antibiotics that are effective against Lyme disease, during the later stages large amounts are need and the symptoms often persist. See the Youtube video below for a firsthand account of what it is like to have Lyme disease.
Along the west coast the vector for Lyme disease is Ixodes pacificus. Throughout the rest of the United States the vector for Lyme disease is Ixodes scapulari (commonly known as the blacklegged tick or deer tick), which can be found in much of the eastern United States. The tick undergoes four stages of development: egg, larva, nymph, and adult. During each mobile stage it feeds on a different host animal so that it can molt and move on to the next stage. Larvae feed on the blood of mice or birds, primarily on Peromyscus leucopus (the white-footed mouse). This is the stage where they are most likely to become infected with pathogens, which are passed on to the subsequent life stages (known as trans-stadial transmission). Nymphs and adults feed on larger hosts such as raccoons, deer, people, and pets. When the tick feeds its saliva, metabolites, and excess fluids are secreted back to the host. It is during this step, usually beginning 24 hours after attachment to the host, that pathogens are transmitted to the host organism. Humans are at the greatest risk of contracting any of these diseases during the summer months. This is due to the fact that nymphs are the most active between May and August and many of our outdoor activities take place during that time. Immature ticks can also attach to humans, but often go unnoticed due to their tiny size Refer to the life cycle diagram on the side of the blog for more details.
References:
Patnaude, M. R. (July 2000). Featured Creatures. Retrieved from http://entnemdept.ufl.edu/creatures/urban/medical/deer_tick.htm
Nemose. (March 2010). Ixodes Scapluaris, black-Legged Tick, Deer Tick-Vector of Lyme Disease. Retrieved from http://www.metapathogen.com/tick/
Tortora, G. J., Funke, B. R., Case, C. L. (2010). Microbiology: An introduction (10th ed) (pp. 653-654). San Francisco, CA: Pearson Benjamin Cummings.


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