25.2 Bacterial infections of the circulatory and lymphatic systems  (Page 18/24)

In both louse- and tickborne relapsing fevers, bacteremia usually occurs after the initial exposure, leading to a sudden high fever (39–43 °C [102.2–109.4 °F) typically accompanied by headache and muscle aches. After about 3 days, these symptoms typically subside, only to return again after about a week. After another 3 days, the symptoms subside again but return a week later, and this cycle may repeat several times unless it is disrupted by antibiotic treatment. Immune evasion through bacterial antigenic variation is responsible for the cyclical nature of the symptoms in these diseases.

The diagnosis of relapsing fever can be made by observation of spirochetes in blood, using darkfield microscopy ( [link] ). For louseborne relapsing fever, doxycycline or erythromycin are the first-line antibiotics. For tickborne relapsing fever, tetracycline or erythromycin are the first-line antibiotics.

Trench fever

The louseborne disease trench fever was first characterized as a specific disease during World War I, when approximately 1 million soldiers were infected. Today, it is primarily limited to areas of the developing world where poor sanitation and hygiene lead to infestations of lice (e.g., overpopulated urban areas and refugee camps). Trench fever is caused by the gram-negative bacterium Bartonella quintana , which is transmitted when feces from infected body lice, Pediculus humanus var corporis , are rubbed into the louse bite, abraded skin, or the conjunctiva. The symptoms typically follow a 5-day course marked by a high fever, body aches, conjunctivitis, ocular pain, severe headaches, and severe bone pain in the shins, neck, and back. Diagnosis can be made using blood cultures; serological tests like ELISA can be used to detect antibody titers to the pathogen and PCR can also be used. The first-line antibiotics are doxycycline , macrolide antibiotics , and ceftriaxone .

Tick tips

Many of the diseases covered in this chapter involve arthropod vectors. Of these, ticks are probably the most commonly encountered in the US. Adult ticks have eight legs and two body segments, the cephalothorax and the head ( [link] ). They typically range from 2 mm to 4 mm in length, and feed on the blood of the host by attaching themselves to the skin.

Unattached ticks should be removed and eliminated as soon as they are discovered. When removing a tick that has already attached itself, keep the following guidelines in mind to reduce the chances of exposure to pathogens:

• Use blunt tweezers to gently pull near the site of attachment until the tick releases its hold on the skin.
• Avoid crushing the tick's body and do not handle the tick with bare fingers. This could release bacterial pathogens and actually increase your exposure. The tick can be killed by drowning in water or alcohol, or frozen if it may be needed later for identification and analysis.
• Disinfect the area thoroughly by swabbing with an antiseptic such as isopropanol.
• Monitor the site of the bite for rashes or other signs of infection.

Many ill-advised home remedies for tick removal have become popular in recent years, propagated by social media and pseudojournalism. Health professionals should discourage patients from resorting to any of the following methods, which are NOT recommended:

• using chemicals (e.g., petroleum jelly or fingernail polish) to dislodge an attached tick, because it can cause the tick to release fluid, which can increase the chance of infection
• using hot objects (matches or cigarette butts) to dislodge an attached tick
• squeezing the tick's body with fingers or tweezers

Bacterial infections of the circulatory and lymphatic systems

Although the circulatory system is a closed system, bacteria can enter the bloodstream through several routes. Wounds, animal bites, or other breaks in the skin and mucous membranes can result in the rapid dissemination of bacterial pathogens throughout the body. Localized infections may also spread to the bloodstream, causing serious and often fatal systemic infections. [link] and [link] summarize the major characteristics of bacterial infections of the circulatory and lymphatic systems.

Key concepts and summary

• Bacterial infections of the circulatory system are almost universally serious. Left untreated, most have high mortality rates.
• Bacterial pathogens usually require a breach in the immune defenses to colonize the circulatory system. Most often, this involves a wound or the bite of an arthropod vector, but it can also occur in hospital settings and result in nosocomial infections.
• Sepsis from both gram-negative and gram-positive bacteria , puerperal fever, rheumatic fever, endocarditis, gas gangrene, osteomyelitis, and toxic shock syndrome are typically a result of injury or introduction of bacteria by medical or surgical intervention.
• Tularemia, brucellosis, cat-scratch fever, rat-bite fever, and bubonic plague are zoonotic diseases transmitted by biological vectors
• Ehrlichiosis, anaplasmosis, endemic and murine typhus, Rocky Mountain spotted fever, Lyme disease, relapsing fever, and trench fever are transmitted by arthropod vectors.
• Because their symptoms are so similar to those of other diseases, many bacterial infections of the circulatory system are difficult to diagnose.
• Standard antibiotic therapies are effective for the treatment of most bacterial infections of the circulatory system, unless the bacterium is resistant, in which case synergistic treatment may be required.
• The systemic immune response to a bacteremia, which involves the release of excessive amounts of cytokines, can sometimes be more damaging to the host than the infection itself.

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