Rickettsial spotted fevers

# Overview
Rickettsia is a genus of non-motile, Gram-negative, non-sporeforming, highly pleomorphic bacteria that can present as cocci (0.1 m in diameter), rods (1-4 m long) or thread-like (10 m long). Obligate intracellular parasites, the Rickettsia  depend on entry, growth, and replication within the cytoplasm of eukaryotic host cells (typically endothelial cells). Because of this, Rickettsia cannot live in artificial nutrient environments and are grown either in tissue or embryo cultures (typically, chicken embryos are used).  In the past they were regarded as microorganisms positioned somewhere between viruses and true bacteria. The majority of Rickettsia bacteria are susceptible to antibiotics of the tetracycline group.
Rickettsia species are carried as parasites by many ticks, fleas, and lice, and cause diseases such as typhus, rickettsialpox, Boutonneuse fever, African Tick Bite Fever, Rocky Mountain spotted fever, Australian Tick Typhus, Flinders Island Spotted Fever and Queensland Tick Typhus  in human beings.  They have also been associated with a range of plant diseases. Like viruses, they grow only in living cells.  The name rickettsia is often used for any member of the Rickettsiales. They are thought to be the closest living relatives to bacteria that were the origin of the mitochondria organelle that exist in most eukaryotic cells.
The method of growing rickettsia in chicken embryos was invented by Ernest William Goodpasture and colleagues at Vanderbilt University in the early 1930s. 

# Etymology
- The genus Rickettsia is named after Howard Taylor Ricketts (18711910), who worked on and eventually died of typhus. 

# Human pathogenesis
- Transmission occurs as a result of a bite from an infected tick or mite as well as the fecal content of rickettsia infected fleas and lice.
- Rickettsiae enter the bloodstream following inoculation.
- Infection usually occurs within the endothelium as well as smooth muscle cells.
- Bacterial infection progresses with binary fission within the cytosol.
- Infected target cells undergo immense damage.
- A host defense includes a T-lymphocyte-mediated immunological response.
- This includes the presence of gamma interferons and tumor necrosis factor alpha.

# Genomics
- Certain segments of Rickettsial genomes resemble that of mitochondria.
- The deciphered genome of R. prowazekii  is 1,111,523 bp long and contains 834 protein-coding genes.
- Unlike free-living bacteria, it contains no genes for anaerobic glycolysis or genes involved in the biosynthesis and regulation of amino acids and nucleosides.
- In this regard it is similar to mitochondrial genomes; in both cases, nuclear (host) resources are used. ATP production in Rickettsia is the same as that in mitochondria.
- In fact, of all the microbes known, the Rickettsia is probably the closest "relative" (in phylogenetic sense) to the mitochondria.
- The genome of R. prowazekii contains a complete set of genes encoding for the tricarboxylic acid cycle and the respiratory-chain complex.
- The genomes of the Rickettsia as well as the mitochondria are frequently said to be "small, highly derived products of several types of reductive evolution".

# Classification of rickettsial diseases

# Differentiating between common rickettsial diseases

# Diagnosis

### Physical examination
- Characterized by flu-like symptoms and  blistering rashes.
- If the disease is caused by an infected tick, an eschar, or cutaneous necrosis, is visible at the site of inoculation.

### Laboratory diagnostics
- A confirmatory diagnosis requires a comparative analysis of an acute-phase and convalescent-phase serum antibody titers.

# Risk Factors
- Traveling or residing within endemic regions will increase chances of infection.
- Tick activity is generally heightened during certain the spring and summer months.
- Within endemic regions, tick may choose an animal host, including a domesticated animal such as a dog or cat.
- Although rare, cases of blood transfusion and organ transplantation have been recorded as methods of transmission.
- All together, individuals who spend time outdoors and/or have pets that go outdoors in endemic regions are at risk for tick-borne disease. 

# Treatment

## Medical Therapy
- Antibiotic treatment is often justified based on clinical presentation alone. However all clinical treatments must be tailored according to a patients personal profile; considering age, immunocompetance, pregnancy, allergen profile, splenic function, and current medical status. 
- If there is a collection of pus, the area will need to be incised and drained.

# Prevention
- Rickettsia infections are most often caused by the bite of an infected mite or tick.
- Tick transmission occurs over the course of a blood meal, therefore the early and proper removal of an infected tick may help evade a potential infection. (For instructions on properly removing a tick, please see "the best way to remove a tick" section below.
- Avoidance of endemic areas is the most effective tactic in preventing a rickettsial infection.
- If it's impossible to avoid endemic areas, common techniques to limit tick exposure may be found in the "limiting tick exposure" section below.
- Other methods of transmission include the fecal matter of infected lice and mites. Thus prevention would include maintaining proper hygiene.

## Limiting tick exposure
It is unreasonable to assume that a person can completely eliminate activities that may result in tick exposure. Therefore, prevention measures should emphasize personal protection when exposed to natural areas where ticks are present:
- Wear light-colored clothing which allows you to see ticks that are crawling on your clothing.
- Tuck your pants legs into your socks so that ticks cannot crawl up the inside of your pants legs.
- Apply repellents to discourage tick attachment. Repellents containing permethrin can be sprayed on boots and clothing, and will last for several days. Repellents containing DEET (n, n-diethyl-m-toluamide) can be applied to the skin, but will last only a few hours before reapplication is necessary. Use DEET with caution on children.  Application of large amounts of DEET on children has been associated with adverse reactions.
- Conduct a body check upon return from potentially tick-infested areas by searching your entire body for ticks. Use a hand-held or full-length mirror to view all parts of your body. Remove any tick you find on your body.
- Parents should check their children for ticks, especially in the hair, when returning from potentially tick-infested areas.
- Ticks may also be carried into the household on clothing and pets and only attach later, so both should be examined carefully to exclude ticks.

## The best way to remove a tick
- Use fine-tipped tweezers or notched tick extractor, and protect your fingers with a tissue, paper towel, or latex gloves. Persons should avoid removing ticks with bare hands.
- Grasp the tick as close to the skin surface as possible and pull upward with steady, even pressure. Do not twist or jerk the tick; this may cause the mouth-parts to break off and remain in the skin. (If this happens, remove mouth-parts with tweezers. Consult your health care provider if illness occurs.)
- After removing the tick, thoroughly disinfect the bite site and wash your hands with soap and water.
- Do not squeeze, crush, or puncture the body of the tick because its fluids may contain infectious organisms. Skin accidentally exposed to tick fluids can be disinfected with iodine scrub, rubbing alcohol, or water containing detergents.
- Save the tick for identification in case you become ill. This may help your doctor to make an accurate diagnosis. Place the tick in a sealable plastic bag and put it in your freezer. Write the date of the bite on a piece of paper with a pencil and place it in the bag. 

# Future or investigational therapies
- The recent discovery of another parallel between Rickettsia and viruses may become a basis for fighting HIV infection.
- Human immune response to the scrub typhus pathogen, Orientia tsutsugamushi rickettsia,  appears to provide a beneficial effect against HIV infection progress, negatively influencing the virus replication process.
- A probable reason for this actively studied phenomenon is a certain degree of homology between rickettsia and the virus - namely, common epitope(s) due to common genome fragment(s) in both pathogens.
- Another infection reported to be likely to provide the same effect (decrease in viral load) is the virus-caused illness dengue fever.