Friday, April 22, 2011

Tick Pathogens


In the United States, some ticks carry pathogens that can cause human diseases. Not all ticks carry a disease or are harmful, but if one that has the tick borne disease should bite you it can have a broad degree of severity in humans. Ticks feed on many vertebrates such as dogs, medium sized mammals and small rodents. The two most common species of tick vectors in the United States are the American dog tick, and the Rocky mountain wood tick.

In North America, Rickettsia rickettsii is transmitted by the American dog tick, and the Rocky mountain wood tick. R. Rickettsii is a rod shaped bacterium known to cause Rocky Mountain Spotted Fever. Ticks are infected with R. Rickettsii while feeding on blood from the host in the larval, nymphal or adult stage. Once the tick gains this pathogen from its host, they remain infected for life. After an immature tick develops into the next stage of its life it can be passed on to the secondary host.

Ticks perch in low vegetation and wait for a susceptible host on which they can attach and feed on. Various online sources describe how ticks enter a host cell. First the R. Rickettsii attach to a protein-dependent receptor on the cell membrane of the host. The cell wall of R.Rickettsii is composed of the outer membrane, peptidoglycan, and cytoplasmic membrane. This makes it hard to stain with the Gram stains and view under the microscope. Secondly, with the aid of the outer membrane Protein A (ompA), the adhesion of this molecule to the host cell induces the local cytoskeleton arrangements with the cell, which results in their entry into the cell. Once a tick attaches to its host, some are known to secrete a cementing material to fasten themselves to the host. Some ticks secrete an anticoagulant, immunosuppressive, and anti inflammatory substance into the area of the tick bite to help the tick obtain a blood meal without the host noticing. The same substances help any freeloading pathogens to establish a foothold in the host.

The Damage following R. Rickettii happens in the blood vessels of the human body, mostly in the brain, skin, and the heart. The bacteria are able to live in the cytoplasm of the nucleus of the host cell. When that bacteria replicate, the results are severe damage and often death of the cells in which it lives in. During multiplication, blood leaks out into nearby tissues through holes in the vessel walls. This obstructs the flow of blood. This part of the cycle involving injury to the blood vessels causes the rash associated with Rocky Mountain spotted fever, in addition to other symptoms including stupor and terminal shock. Death is often caused through excessive damage to the endothelial cells, resulting in the leaking of plasma, decrease in blood volume and shock.

Ticks can transmit many pathogens such as; bacteria, spirochetes, Rickettsia, protozoa, viruses, nematodes and toxins. Tick bite contraindications can resemble arthritis, or flulike symptoms, so it is always a good idea to check yourself anytime after a camping event, or if you have animals that may carry them on their fur. Taking the time to check yourself can prevent a wide variety of symptoms from something as simple as a rash or to something as dangerous as paralysis, shock, or death. Some bites can be cured with and antibiotic, unless it has invaded the Central Nervous System.

References:
1.) http://microbewiki.kenyon.edu/index.php/Rickettsia_rickettsii

2.)http://www.bio.davidson.edu/people/sosarafova/Assets/Bio307/liwoeste/PathogenLifeCycle.html

3.)http://emedicine.medscape.com/article/786652-overview

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