Pathology And History Of Rickettsia Rickettsii Biology Essay


Although it is not a common disease here in West Virginia, a rickettsial illness known as the Rocky Mountain spotted fever (Rickettsia rickettsii) is somewhat familiar to those who live in the South Atlantic region of the United States(CDC, 2005). According to emedicine, a rickettsial illness is caused by organisms within the genus of rickettsiae. There are four groups of illness caused by this particular bacterium, Rickettsia rickettsii being the most reported in the United States.

This particular organism is a small bacterium which ranges from 0.2 x 0.5mm - 0.3 x 2.0mm. Due to its small size, it is difficult to see in the body tissues using ordinary stains and in most cases are found using special staining methods. This bacterium lives among the cells that line the blood vessels and once they are inside of their host they begin to multiply. The rapid multiplying of these cells cause damage and death to the cells which lead to fissures within the vessel. Due to the fissures among the vessels, blood begins to leak through which is the cause of the rash seen on a patient with the Rocky Mountain spotted fever (CDC, 2005).

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This illness was first known as "black measles" due to the rash which is present prior to the bite of the infectious tick. The Rocky Mountain spotted fever was first described in the late 1800s and was thought to only be a problem within the Rocky Mountains. This misunderstanding of the location of the illness gave it the name that it has today (Black, 2006). Although it was once known to only be in the Rocky Mountain region of the United States, statistics now show that only 3% of the reported cases were within that region and that most reported cases are now within North and South Carolina. Statistics also show that 90% of cases happen between the months of April and September (CDC, 2005). At one point it was very well known and talked about. In 1969, a show referred to as "Doctor in the House" even aired an episode called The Rocky Mountain Spotted Fever Casino.

The Rocky Mountain spotted fever is classified as a zoonosis. According to the Center for Disease Control, zooneses are diseases of animals that can be transmitted to humans. Most zoonotic diseases require a natural host to transmit a disease from the animal to the human host. In the case of the Rocky Mountain spotted fever, ticks are the natural host being both the reservoir and vector. Ticks can acquire the rickettsia ricketsii bacteria in many ways. The disease causing bacteria can be passed from a male to a female tick through bodily fluids during the matting process; the female tick can also transmit the pathogen to her eggs causing the infant ticks to be born with the bacteria as well. Once a tick is infected, it will carry the disease causing bacteria for life (CDC, 2005). They simply transmit the disease by their bite. Rickettsia rickettsii is passed from an infected tick to a human through saliva during the feeding process. It usually takes several hours of attachment and feeding before the pathogen is passed onto the host. In some rare cases, infections could occur due to contact with a tissue which a tick was crushed in or also ticks faeces (Rocky, n.d.). The risk factor of coming in contact with a tick infected with R. ricketsii is very low. According to the Center for Disease Control, only 1%-3% of the tick population carries the disease causing bacterium. Out of the tick population which carries the bacterium, the two most popular vectors are the American dog tick and the Rocky Mountain wood tick. The American dog tick is primarily found east of the Rocky Mountains and also in a few areas along the Pacific Coast. This particular tick is most common identified for transmitting the bacteria which causes the Rocky Mountain spotted fever. The Rocky Mountain wood tick is found among the Rocky Mountain States and also along south western Canada (CDC, 2005). Although these two are the most prevalent to carry the disease, other ticks are able to transmit the bacteria as well. The New York Times warns citizens in the North east of diseases carried by deer ticks, and the Rocky Mountain spotted fever was listed as a concern. Rickettsia rickettsii is the second most reported tick borne disease within the United States, Lyme disease being the first (Rocky, n.d.).

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Once a victim of this disease is bit, there are many side effects. The first symptoms begin to appear 5-10 days after the infectious tick bite. The most common symptoms are a fever and rash(see table 5), but may also include nausea, vomiting, severe headache, muscle pain and loss of appetite. Once the rash begins to worsen, other symptoms may become present such as abdominal pain, joint pain and diarrhoea.

There is no quick laboratory testing that can be done to detect this disease and it is treated by clinical clues in most situations. However, there are clinical lab tests that can suggest the sign of Rocky Mountain spotted fever such as abnormal white blood cell count and elevated liver enzyme levels. There is a specific test used by the Center for Disease Control and other public health laboratories to detect the Rocky Mountain spotted fever; it is the indirect immuno fluorescence assay which is also referred to as an IFA.

An IFA can identify both igG and igM antibodies. For an IFA to be used, it is recommended that the patient give blood samples from an early stage and also a late stage of the disease. The earlier blood sample would be used to watch for an increase of igM titers which normally show an increase within the first 7-10 days of the illness. The second blood sample given would be used to watch for a change in the igG titers which normally begin to become present after the first 7-10 days.

Other than the IFA, there is another form of testing known as immuno staining. This particular technique is used after taking a skin biopsy of the rash before medical treatment has begun or within the first 48 hours of administering an antibiotic to the patient. This particular testing can also be used in the case of a death where Rocky Mountain spotted fever is suspected. It can confirm that the patient had a fatal case of the disease (see table 8).

The Rocky Mountain spotted fever is moderately calm if treated as soon as possible. Physicians should treat any clinical clues such as a tick bite leading to a fever with an antibiotic before all testing is even complete. Antibiotics within the tetracycline class are usually prescribed for this illness (CDC, 2005).