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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.

A micrograph showing red circles labeled red blood cells and larger white blood cells. Small spirals (approximately the length of 2 red blood cells; 20 µm) are labeled Borrelia spirochetes.
A peripheral blood smear from a patient with tickborne relapsing fever. Borrelia appears as thin spirochetes among the larger red blood cells. (credit: modification of work by Centers for Disease Control and Prevention)

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 .

  • What is the vector associated with epidemic typhus?
  • Describe the life cycle of the deer tick and how it spreads Lyme disease.

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
a) A tick on a finger. B) a spoon shaped tool with a notch is used to pull the tick. C) tweezers can be used to pull the tick straight out.
(a) This black-legged tick, also known as the deer tick, has not yet attached to the skin. (b) A notched tick extractor can be used for removal. (c) To remove an attached tick with fine-tipped tweezers, pull gently on the mouth parts until the tick releases its hold on the skin. Avoid squeezing the tick’s body, because this could release pathogens and thus increase the risk of contracting Lyme disease . (credit a: modification of work by Jerry Kirkhart; credit c: modification of work by Centers for Disease Control and Prevention)

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.

Table titled: Bacterial Infections of the Circulatory and Lymphatic Systems. Columns: Disease, Pathogen, Signs and Symptoms, Transmission, Diagnostic Tests, Antimicrobial Drugs. Anaplasmosis (HGA); Anaplasma phagocytophilum; Fever, flu-like symptoms; From small-mammal reservoirs via tick vector; Blood smear, PCR; Doxycycline. Brucellosis; Brucella melitensis, B. abortus, B. canis, B. suis; Granuloma, undulating fever, chronic flu-like symptoms; Direct contact with infected livestock or animals; Agglutination tests, ELISA; Doxycycline, rifampin. Cat-scratch disease; Bartonella henselae; Lymph-node swelling and pain, fever, chills, fatigue; Bite or scratch from domestic cats; Immunofluorescence, serological tests, PCR; None for immunocompetent patients. Ehrlichiosis (HME); Ehrlichia chaffeensis;Flu-like symptoms, rash; Lone star tick vector; Serologic tests, PCR; Doxycycline. Endocarditis/pericarditis; Staphylococcus spp., Streptococcus spp., Enterococcus spp., HACEK bacilli; Chest pain, difficulty breathing, dry cough, fever; potentially fatal damage to heart valves; Pathogens introduced to bloodstream via contaminated catheters, dental procedures, piercings, or wounds; Echocardiogram, blood culture; Ampicillin, nafcillin, gentamicin, others; based on susceptibility testing. Epidemic typhus; Rickettsia prowazekii; High fever, body aches, rash; potentially fatal damage to heart and brain; From rodent reservoir via body louse vector; PCR, immunofluorescence; Doxycycline, chloramphenicol. Gas gangrene; Clostridium perfringens, other Clostridium spp.; Rapidly spreading myonecrosis, edema, yellowish and then purple discharge from wound, pockets of gas in tissues, septic shock and death; Germination of endospores in ischemic tissues, typically due to injury or chronic disease (e.g., diabetes); Wound culture; Penicillin G, clindamycin, metronidazole. Infectious arthritis (septic arthritis); Staphylococcus aureus, Neisseria gonorrhoeae; Joint pain and swelling, limited range of motion; Infection spreads to joint via circulatory system from wound or surgical site; Synovial fluid culture; Oxacillin, cefazolin, cephtriaxone. Lyme disease; Borrelia burgdorferi; Early localized: bull’s eye rash, malaise, headache, fever, muscle stiffness; early disseminated: stiff neck, facial paralysis, arthritis, carditis; late-stage: arthritis, meningitis, possibly fatal; From deer, rodent, bird reservoirs via tick vector; IFA, serology, and ELISA; Amoxicillin, doxycycline, penicillin G, chloramphenicol, ceftriaxone. Murine (endemic) typhus; Rickettsia typhi; Low-grade fever, rash, headache, cough; From rodents or between humans via rat flea vector; Biopsy, IFA, PCR; Doxycycline, chloramphenicol. Osteomyelitis; Staphylococcus aureus, Streptococcus pyogenes, others; Inflammation of bone tissue, leading to fever, localized pain, edema, ulcers, bone loss; Pathogens introduced through trauma, prosthetic joint replacement, or from other infected body site via bloodstream; Radiograph of affected bone, culture of bone biopsy specimen; Cephalosporin, penicillins, others.
Table titled: Bacterial Infections of the Circulatory and Lymphatic Systems (continued). Columns: Disease, Pathogen, Signs and Symptoms, Transmission, Diagnostic Tests, Antimicrobial Drugs.Plague; Yersinia pestis; Bubonic: buboes, fever, internal hemorrhaging; septicemic: fever, abdominal pain, shock, DIC, necrosis in extremities; pneumonic: acute pneumonia, respiratory failure, shock. All forms have high mortality rates. Transmitted from mammal reservoirs via flea vectors or consumption of infected animal; transmission of pneumonic plague between humans via respiratory aerosols; Culture of bacteria from lymph, blood, or sputum samples; DFA, ELISA; Gentamycin, fluoroquinolones, others. Puerperal sepsis; Streptococcus pyogenes, many others; Rapid-onset fever, shock, and death; Pathogens introduced during or immediately following childbirth; Wound, urine, or blood culture; As determined by susceptibility testing. Rat-bite fever; Streptobacillus moniliformis, Spirillum minor; Fever, muscle and joint pain, rash, ulcer; Bite from infected rat or exposure to rat feces or body fluids in contaminated food or water; Observation of the organism from samples and antibody tests; Penicillin. Relapsing fever; Borrelia recurrentis, B. hermsii, other Borrelia spp.; Recurring fever, headache, muscle aches; From rodent or human reservoir via body louse or tick vector; Darkfield microscopy; Doxycycline, tetracycline, erythromycin. Rheumatic fever; Streptococcus pyogenes; Joint pain and swelling, inflammation and scarring of heart valves, heart murmur; Sequela of streptococcal pharyngitis; Serology, electrocardiogram, echocardiogram; Benzathine benzylpenicillin. Rocky Mountain spotted fever; Rickettsia rickettsia; High fever, headache, body aches, nausea and vomiting, petechial rash; potentially fatal hypotension and ischemia due to blood coagulation; From rodent reservoir via tick vectors; Biopsy, serology, PCR; Doxycycline, chloramphenicol. Toxic shock syndrome (TSS); Staphylococcus aureus; Sudden high fever, vomiting, diarrhea, hypotension, deathPathogens from localized infection spread to bloodstream; pathogens introduced on tampons or other intravaginal products; Serology, toxin identification from isolates; Clindamycin, vancomycin. Toxic shock-like syndrome (STSS); Streptococcus pyogenes; Sudden high fever, vomiting, diarrhea, acute respiratory distress syndrome (ARDS), hypoxemia, necrotizing fasciitis, death; Sequela of streptococcal skin or soft-tissue infection; [MISSING]; Penicillin, cephalosporin. Trench fever; Bartonella Quintana; High fever, conjunctivitis, ocular pain, headaches, severe pain in bones of shins, neck, and back; Between humans via body louse vector; Blood culture, ELISA, PCR; Doxycycline, macrolide antibiotics, ceftriaxone. Tularemia (rabbit fever); Francisella tularensis Skin lesions, fever, chills, headache, buboes; Eating or handling infected rabbit; transmission from infected animal via tick or fly vector; aerosol transmission (in laboratory or as bioweapon); DFA; Streptomycin, gentamycin, others.

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.

Fill in the blank

Lyme disease is characterized by a(n) ________ that forms at the site of infection.

bull’s eye-rash

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________ refers to a loss of blood pressure resulting from a system-wide infection.

Septic shock

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Short answer

What are the three forms of plague and how are they contracted?

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Compare epidemic and murine typhus.

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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