Clinical Microbiology HW#13

Chapter 23

1. All lymph that returns to the heart must pass through at least one lymph node.

TRUE

2. Which of the following is a symptom of brucellosis?

undulant fever

3. The symptoms of gas gangrene are due to all of the following EXCEPT

Endocarditis

**Symptoms of gas gangrene are due to: necrotizing exotoxins; microbial fermentation; hyaluronidase; proteolytic enzymes.

4. Which of the following pairs is mismatched?

encephalitis – Ixodes (tick)

**match:

malaria – Anopheles (mosquito)

dengue – Aedes (mosquito)

Rocky Mountain spotted fever – Dermacentor (tick)

epidemic typhus – Pediculus (louse)

5. Unsanitary and crowded conditions increase the incidence of all of the following diseases EXCEPT

Rocky Mountain spotted fever

**unsanitary and crowded conditions increase the incidence of all of the following: plague; relapsing fever; epidemic typhus; endemic murine typhus.

6. Human-to-human transmission of plague is usually by

the respiratory route

7. Which of the following leads to all the others?

bacterial growth in endothelial cells

8. Neonatal sepsis is most commonly caused by group A streptococci

FALSE – group B

9. Which of the following can be transmitted from an infected mother to her fetus across the placenta?

Cytomegalovirus

10. Epstein-Barr virus has been implicated in all of the following EXCEPT

Endocarditis

**Epstein-Barr virus has been implicated in all of the following: Burkitt's lymphoma; Hodgkin's disease; nasopharyngeal carcinoma; infectious mononucleosis.

11. A patient complains of fever, severe muscle and joint pain, and a rash. The patient reports returning from a Caribbean vacation one week ago. Which of the following do you suspect?

Dengue

12. Which of the following is NOT transmitted in raw milk?

Toxoplasmosis

**Transmitted in raw milk: listeriosis; brucellosis; anthrax

13. Which of the following statements about toxoplasmosis is FALSE?

It is a severe illness in adults.

**TRUE about toxoplasmosis:

It is transmitted by the gastrointestinal route.

It can be congenital.

The reservoir is cats.

It is caused by a protozoan.

14. Which of the following is NOT caused by a bacterium?

Malaria

**Caused by a bacterium: tickborne typhus; relapsing fever; epidemic typhus; plague

15. Which of the following is NOT controlled by a mosquito eradication program?

Schistosomiasis

**Controlled by a mosquito eradication program: chikungunya fever; yellow fever; dengue fever; malaria.

Chapter 23 Reading Questions

1. Which of the following cell populations become plasma cells?

B cells

2. A patient has a skin ulcer from which a gram-negative bacillus is cultured. This patient has regional lymph nodes that are enlarged and filled with pockets of pus. He reports keeping pet rabbits. Which of the following is a possible diagnosis?

Tularemia

Diseases in Focus Chapter 23 – Female, age 36

Medical History (Hx)

The patient is a female, age 36. She is an assistant professor in philosophy. The patient is married (6 years), sexually active, and monogamous. She does not have any children. She has a history of hypertension on her mother's side of the family. She is allergic to tree nuts. She does not report using any drugs of abuse. She and her husband and pets (a cat, and two dogs) were driving cross-country from San Diego, CA to New York City, NY as part of a move to accept her academic position. During the trip, the couple had planned to stay for a week at her husband's parent's ranch in White Rock, New Mexico. While there, her husband fell ill with fever, fatigue, and a painful lump in his groin (inguinal region). Since the patient had several appointments in New York to keep, she decided to keep driving, while her husband would stay with his parents until he felt well enough to fly to New York with their dogs. The patient reports starting to feel “ill” during her first couple of days in New York. She had noticed a mild fever; however she did not seek medical attention until she developed a painful inguinal swelling similar to her husband. Soon after, she developed fever and chills.

Differential Diagnoses

Differential diagnosis is the process of identifying a disease from a list of possible diseases that fit the information derived from examining a patient. Your job will be to synthesize information from a patient whose main presenting symptoms are consistent with a microbial disease of the cardiovascular and lymphatic system. Use the "Diseases in Focus 23.2 and 23.3" table and your knowledge about microbial diseases of the cardiovascular and lymphatic systems to identify the patient's risk factors and symptoms, evaluate diagnostic evidence, formulate and test a diagnosis about the pathogen responsible for the patient's woes, and suggest a course of treatment.

1. Identify relevant information

Review the patient's medical history, and then identify risks and concerns that are relevant to your diagnosis (and the patient's treatment).

Relevant:

Risk of vector-borne disease

Risk of travel-related disease exposure

Not Relevant:

Age-related risk of disease

Occupational risk of disease

Risk of sexually transmitted infection (STI)

Risk of drug-related disease exposure

Risk of genetic/familial disease

Special concerns for treatment

Risk of immunocompromised

2. Review Possible Diagnoses

Now that you have considered the evidence at hand, you should start to build a hypothesis about what disease your patient has. As you ponder her symptoms, you find yourself particularly troubled by her groin swelling. Groin (or inguinal) swellings can be a common symptom of a variety of sexually transmitted infections including herpes (genitalis and simplex), syphilis, chancroid, and lymphogranuloma venereum, among others. Your patient has been in a monogamous relationship for 6 years however, and does not report using any drugs of abuse. While it is still possible that your patient has contracted a sexually transmitted infection, you also would like to consider other disease possibilities.

Cat-scratch disease

Tularemia

Plague

Chagas’ disease

**Your patient's symptoms and medical history are consistent with several different diseases. One possibility is that your patient's inguinal swelling could be a papule or lymph swelling associated with cat-scratch disease. She does own a cat, and could've easily been scratched at some point during her trip. Similarly, her swelling could also be symptomatic of tularemia, plague, or Chagas' disease. All of these diseases are relatively uncommon, and require relatively specific exposure conditions, however your patient's recent travel history, and pets, could've exposed her to a number of disease vectors. Reviewing these choices, you become immediately alarmed! You send out an emergency page throughout the department, and two other doctor's quickly come running.

3. Identify special conditions

"What is the matter?!" one of the doctors asks. You take another glance at your chart, and then respond that your patient could be infected with a disease that:

is caused by an agent of bioterrorism

**The plague has the potential to be used as a bioweapon. New York City is a densely populated area, and if your patient did not acquire the disease in a region where plague is known to be endemic (naturally occurring), it could indicate a bioterrorism risk!

4. There are several different forms of the plague. Which form is of the greatest concern as a potential bioweapon?

Pneumonic plague

**Pneumonic plague affects the lungs. It can be spread from person to person by inhaling bacterial particles in the air. Thus, for this reason and others, we are concerned about the bioterrorism potential of pneumonic plague in an aerosol attack. The pathogen responsible for pneumonic plague is naturally occurring, and could be isolated and grown in quantity in a lab. In addition, the delay between infection and the appearance of the disease could quickly spread the pathogen to a large number of people before it could be controlled.

5. Select course of action

Since you suspect your patient could have the plague, you must confirm your diagnosis as soon as possible! Select the most appropriate samples to establish that you patient does or does not have the plague, and if these samples come back positive; which sort of plague.

Blood

Fluid from your patient’s inguinal swelling

Sputum (mucus from lower airways)

**You should take samples of the patient's blood, aspirate of the patient's inguinal swelling, and a sample of sputum. You test these samples for the causative agent of the plague.

6. Interpret your results

Your laboratory results are shown here: 

Fluid	Rapid diagnostics: (detection of F1 antigen by immunoflourescent assay)	Culture	Stain
Blood	negative	negative	Gram-stain: negative
Aspirate from lymph node	positive	positive	Gram-stain: positive
Sputum	negative	negative	Wayson stain: negative

Does your patient have the plague? Can you say which form?

Yes, she has bubonic plague

7. Diagnose the causative organism

The stain of the cultured organisms from your patient's swollen lymph node reveals bipolar Gram-negative rods, with a "safety pin" appearance. Which organism is directly responsible for your patient's woes?

Yersinia pestis

Consider new evidence!

Since your patient has been ill, she has not been able to contact her husband or family. You decide to call them and let them know her situation. Her family does not answer their home phone, but eventually you are able to contact her father-in-law on his cell phone. He informs you that your patient's husband was admitted to the hospital in New Mexico when his condition worsened. Since your patient's departure, her husband has been severely ill with diarrhea, abdominal pain, vomiting, and low blood pressure. Yesterday, he developed massive bleeding under his skin, and bruises around his swollen lymph node. In addition, he developed black, gangrenous finger tips on both of his hands. Diagnostics showed bacteremia and severe sepsis. He was treated with gentamycin, vancomycin, ciprofloxacin, doxycycline, and human activated protein C, but his condition worsened. His blood pressure dropped dramatically, and his kidneys began to fail. He was placed on mechanical ventilation and hemodialysis, and underwent unilateral amputation of one of his hands due to ischemia.

8. Review Possible Diagnoses

What do you think is wrong with your patient's husband?

He has septicemic plague.

9. Refine your hypothesis

Which of the following can best explain the symptoms and deterioration of your patient's husband?

Gram-negative sepsis

Endotoxic shock

Disseminated intravascular coagulation

10. Select a follow-up

You contact the New York City Department of Health and Mental Hygiene, as well the New Mexico Department of Health, and update them on the cases you have diagnosed. Both agencies are eager to locate where and how the infections were first contracted. Where will you recommend that investigators FIRST look for the source of infection?

The couple's parent's ranch in New Mexico

11. What sort of organisms would you instruct investigators to test for plague?

Rats and mice

Ground squirrels and rabbits

Household pets (cats and dogs)

Wild predators

**Investigators follow your lead and check out the rodent, rabbit, predator, and domestic animal populations at the couple's parent's New Mexico ranch. Extensive sampling reveals several infected rock squirrels, as well as an infected woodrat carcass. The infected rock squirrel populations are exterminated. One of the couple's dogs also tested positive for Y. pestis antibodies. Fortunately, all known cases of dogs infected orally with Y. pestis progress only to fever, and the dogs are able to recover. The dog is placed in quarantine until the infection is fully cleared.

Through your quick thinking, your hospital, and the hospital in New Mexico has successfully diagnosed two patients with the plague! For animals and humans, plague is a reportable disease in the United States. In this case, your quick thinking was instrumental in timely notification of local and state health departments, federal animal health officials, and the CDC's National Center for Infectious Diseases (Meningitis and Special Pathogens Branch). In addition, diagnostic laboratories were informed of the outbreak, such that safe processing protocols were followed, and no further infections resulted.

Although your patient's husband lost one of his hands, he is otherwise responding to antibiotics, and recovering well. Fortunately, you were able to catch your patient's disease before it got much worse, and the course of streptomycin and tetracycline you prescribed to her is working well.

Rocky Mountain spotted fever: A Tale of Two Friends, Backpacking, and Ticks

Ron and Paul went backpacking in the Bitterroot Mountains of Montana in mid-June. The weather was good, and the trip was uneventful, except for the large numbers of ticks the pair noticed, seemingly everywhere. The pair used insect repellant on their clothes, and Paul advised Ron to check himself for ticks when they got back to their homes.

Seven days later, Ron begins to develop flulike symptoms, including a fever, muscle aches, and a severe headache. After two days of bed rest, he doesn’t feel any better and actually begins to get worse. He becomes nauseated and seems very lethargic and confused to his wife. His wife takes him to their family physician, who agrees that it seems like a bad case of the flu, even though it is not flu season and the doctor has not noticed any rise in influenza infections recently. When asked about his recent activities, Ron mentions that he had gone backpacking a couple of weeks earlier, but he doesn’t mention the area where he traveled or the ticks. The doctor has blood drawn for routine testing and sends Ron home with orders for bed rest and fluids.

The next day, Ron’s wife receives a phone call from the doctor’s office, informing her that she should bring Ron into the hospital for more testing. The blood testing performed the day before had revealed leukocytosis (high white blood cell count) and severe thrombocytopenia (relative decrease of platelets). Ron has begun to develop a macropapular rash on his hands and feet and is feeling worse than ever.

He is admitted to the hospital, and more testing is ordered.

That afternoon, Paul calls Ron to see whether he wants to go hiking the next weekend. Ron’s wife answers the phone and lets Paul know that Ron is in the hospital and very sick. After she describes the symptoms, Paul asks whether the doctors have been informed that Ron was likely exposed to a tick bite. She says she doesn’t think so, and Paul tells her that she should tell the doctors right away.

1. What disease does Paul suspect Ron might have contracted?

Rocky Mountain spotted fever

**Rocky Mountain spotted fever (RMSF) is a tickborne disease caused by Rickettsia rickettsii. In the United States, there are two primary tick vectors: Dermacentor andersoni (in the western United States) and Dermacentor variablis (in the eastern United States).

Ron is experiencing the classic triad of symptoms associated with RMSF: fever, headache, and macular rash.

2. What part of the United States is endemic for RMSF?

the Appalachian region (North Carolina, Kentucky)

**In the early 1900s, settlers in the Bitterroot Valley were victim to what they called the “black measles.” The infection seemed concentrated on the west side of the Bitterroot River and was fatal in four out of five cases. In 1928, the Rocky Mountain Laboratory (RML) was established in Hamilton, Montana (very near to where Paul and Ron went backpacking) to study RMSF. Residents of the area were terrified that ticks would be able to escape the facility and spread disease. Therefore, a small moat was built around the facility to help contain the ticks!

In 1906, Dr. Howard Ricketts identified that the disease was transmitted by the bite of D. andersoni, and in 1909 he isolated the causative organism (later named Rickettsii rickettsii in his honor). R. rickettsii is a small gram-negative pleomorphic coccobacillus and is an obligate intracellular parasite.

3. Rickettsia rickettsii is a gram-negative, obligate intracellular pathogen. Which of the following statements about the R. rickettsii life cycle is FALSE?

After entering a host, R. rickettsii multiplies to levels high enough to successfully invade cells and establish an infection.

**TRUE:

During infection, R. rickettsii is able to survive and replicate within eukaryotic cells.

Like viruses, R. rickettsii requires a eukaryotic host in order to carry out its life cycle.

In order to cause RMSF, R. rickettsii must enter host cells.

***As an obligate intracellular organism, R. rickettsii must carry out its entire life cycle within a eukaryotic cell. In order for R. rickettsii to invade cells, it has to adhere to host cells and enter. This does not require cells to multiply; remember that R. rickettsii is unable to multiply in the external environment. This means that to be grown for study in the laboratory, R. rickettsii has to be grown within host cells. During infection, R. rickettsii carries out its life cycle in host cells; in fact, it spreads from cell to cell without ever leaving the cell. It induces the formation of projections from one cell to another, allowing it to spread without ever leaving the protective environment of the host cell.

The infective life cycle of R. rickettsii also involves the vector Dermacentor andersoni. It is likely that Ron was infected after biological transmission of R. rickettsii.

4. Which of the following is a characteristic of biological transmission from Dermacentor to a human host?

R. rickettsii is transmitted to the human host during a bite, when tick saliva enters the wound.

**R. rickettsii resides within the salivary glands of the Dermacentor tick. It exists in a “dormant” state until the tick feeds for an extended period of time. While the tick is biting the human, the R. rickettsii bacteria are transmitted to the human and released into the circulatory system. The transmission of R. rickettsii from the tick to the host requires at least 6 to 10 hours from the moment the tick attaches to the host.

5. RMSF results from the interactions that occur between the R. rickettsii pathogen and the host. The infection results from a coordinated series of events that ultimately result in disease.

1. Tick bites transmit R. rickettsia into bloodstream.

2. R. rickettsii travels throughout the body via the blood and lymph systems.

3. R. rickettsia invades endothelial cells of blood vessels.

4. R. rickettsia multiplies within host cells

5. Blood begins to escape from vessels as a result of increased vascular permeability.

6. Symptoms, such as a macular rash, develop.

**Once introduced into the bloodstream from a tick bite, R. rickettsii will spread throughout the body via the blood/lymph system. R. rickettsii invades endothelial cells that line the vessels and remains protected from the immune system. The subsequent spread from cell to cell results in significant endothelial cell damage and increased vascular permeability. This increased permeability leads to leakage of blood from the vessels, which manifests as the macular rash. In very severe cases, the extensive damage can cause occlusion of the small vessels, leading to gangrene and possible amputation or debridement of necrotic tissue.

***As soon as Ron’s physicians become aware that Ron was exposed to ticks and therefore has possibly been infected with R. rickettsii, they immediately start him on intavenous doxycycline. Over the next few days, Ron’s condition markedly improves, and he is allowed to go home, with no apparent complications from the disease.

6. The IV regimen administered by Ron’s doctors is consistent with the CDC’s recommendation that doxycycline be administered when RMSF is suspected. Apply your knowledge of RMSF to choose the most likely reasons behind this recommendation.

Most tests that can definitively identify R. rickettsii are not very effective early in infection.

A delay in treatment can lead to complications that include respiratory, cardiac, and renal failure.

The symptoms of RMSF are similar to those of several other infections, making definitive diagnosis difficult.

Without prompt treatment, RMSF can have a mortality rate as high as 20%.

**Tetracyclines (particularly doxycycline) are effective in treating RMSF. It is important to treat patients suspected of RMSF immediately, because a delay in treatment may lead to serious complications from the disease, including severe neurological, ophthalmological, respiratory, gastrointestinal, and renal complications. It may also cause cardiac problems; RMSF is the only tickborne disease that can cause congestive heart failure. Prior to antibiotic treatments, mortality from RMSF was approximately 30%; today, that rate is 3% to 5%. Of the 111 cases studied in the Bitterroot Valley in the early 1900s, 69% were fatal.

Because RMSF is a reportable disease, Ron’s doctors conduct further testing to confirm R. rickettsii as the causative agent.

7. An indirect immunofluorescence assay is described as the CDC “gold standard serological test” for RMSF. Keeping in mind the principles behind indirect fluorescent-antibody (indirect FA) testing, which of the following characteristics contributes to its choice as the gold standard?

Indirect FA will detect R. rickettsii-specific antibodies present in the patient’s serum.

Indirect FA is more sensitive than direct immunofluorescent testing.

Indirect FA is rapid, sensitive, and specific.

Indirect FA uses an antibody that reacts with any human antibody.

**During the indirect FA assay, patient serum is mixed with a sample of R. rickettsii antigens. If the patient’s serum contains R. rickettsii-specific antibodies (indicative of infection), they will bind to the antigens. These antigen-antibody complexes are then detected with a fluorescently labeled antibody specific for human immunoglobulin. Therefore, fluorescence indicates the presence of the antigen-antibody interactions. This approach is more sensitive than the direct approach (which detects the presence of antigens in the serum) for a couple of reasons. First, the level of antigens in the sample (particularly serum from RMSF patients) may be too low to detect. In addition, each step involving antibody binding represents an “amplification” of the signal as multiple antibody molecules can bind to each target. When indirect FA is used in RMSF diagnosis, samples are typically taken early in the infection and then later (2 to 4 weeks later). The early samples will usually have low levels of antibodies; however, the later samples usually show a significant increase in antibody levels.

Chapter 23

1. All forms of typhus are associated with arthropod vectors.

FALSE