Clinical Microbiology HW#12

Chapter 22

1. All of the following organisms are transmitted via the respiratory route EXCEPT

Listeria monocytogenes

Transmitted via respiratory:

Neisseria meningitides

Haemophilus influenza

Cryptococcus neoformans

2. Microscopic examination of cerebrospinal fluid reveals gram-positive rods. What is the organism?

Listeria

3. Viral meningitis is much more common than bacterial meningitis and tends to cause a milder form of disease

TRUE

4. Which of the following statements about leprosy is FALSE?

Patients with leprosy must be isolated

TRUE:

It is rarely fatal.

It is transmitted by direct contact.

Diagnosis is based on skin biopsy.

The etiologic agent is acid-fast.

5. Initial treatment for tetanus in an unimmunized person with a puncture wound is

tetanus immune globulin

6. On October 5, a pet store sold a kitten that subsequently died. On October 22, rabies was diagnosed in the kitten. Between September 19 and October 23, the pet store had sold 34 kittens. Approximately 1000 people responded to health care providers following local media alerts. These people were given

postexposure prophylaxis

7. Which of the following vaccines can cause the disease it is designed to prevent?

oral polio vaccine

8. All of the following are true of poliomyelitis EXCEPT

most cases result in muscle paralysis

True of poliomyelitis:

The majority of cases are asymptomatic.

Initial sites of viral replication are the throat and small intestine.

Infection is due to ingestion of contaminated water.

The oral polio vaccine contains attenuated strains of the virus.

9. If a normal protein typically found on the surface of nervous tissue cells comes into contact with an abnormally folded protein, it can lead to prion-related disease.

TRUE

Chapter 22 Reading Questions

1. Which of the following statements concerning the blood-brain barrier is FALSE?

Penicillin is useless against infections of the brain because it is completely incapable of crossing the barrier.

True concerning the blood-brain barrier:

Inflammation can alter the blood-brain barrier, increasing the likelihood that a substance can cross.

Most antibiotics cannot cross the blood-brain barrier.

Substances that are lipid-soluble can cross the blood-brain barrier readily.

2. If a person in the United States is exposed to rabies, which animal is the most likely culprit?

wild bats

3. Which of the following is an accurate description of Cryptococcus neoformans?

It is a fungus found in dried pigeon droppings. When inhaled, it is especially dangerous to immunocompromised individuals and can cause fatal meningitis.

4. Which of the following is an accurate statement concerning the Sabin and Salk vaccines?

The Sabin vaccine is slightly more dangerous because it is made from live, attenuated virus, and the virus occasionally reverts back to its pathogenic form.

5. Which statement regarding arboviral encephalitis is FALSE?

The most effective preventive measure for arboviral infections is vaccination.

**Mosquito control is the best method of prevention.

True regarding arboviral encephalitis:

Most human cases of West Nile virus (WNV) are subclinical or very mild.

The incidence of disease increases during summer months.

Horses, as well as humans, are frequently affected by arboviruses.

6. Postexposure treatment for rabies includes vaccination and injection of immunoglobulin; these are generally successful if treatment is obtained immediately following exposure. Why does post-exposure vaccination work?

The infection progresses so slowly that there is time for post-exposure vaccination to generate immunity.

Diseases in Focus Chapter 22 – Male, age 74

MEDICAL HISTORY (Hx)

The patient is a 74-year old man who lives in an retirement community in Rancho Cucamonga, California. He was diagnosed with prostate cancer a year ago, and is currently undergoing radiation therapy. He is divorced, and not currently sexually active. He does not own any pets. He took a trip with his son's family to the Great Smoky Mountains within the last year. During this trip, he stayed in a family cabin, which was not used very often. He noted that the screen enclosing the cabin's porch had a hole in it, which permitted several animals to take up residence in the eaves of the porch. As a result, he and his family had to clean up mouse and bird droppings, which had accumulated. He also recalled being bitten by mosquitoes several times. He has a history of hypertension on his mother's side of the family. He does not have any allergies. He does not use drugs of abuse. His chart shows that last week, during a check-up related to his radiation therapy, he complained of a headache and a stiff neck (nuchal rigidity). Since then, the patient says he has developed a fever, which had gotten progressively more severe. The patient was admitted to the hospital for fever and tremors (involuntary shaking movements).

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 central nervous system (CNS). Use the "Diseases in Focus Chapter 22 tables" and your knowledge about microbial diseases of the CNS 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. Review the patient's medical history, and then identify risks and concerns that are relevant to your diagnosis (and the patient's treatment).

Relevant:

Age-related risk of disease

Risk of vector-borne disease

Risk of travel-related disease exposure

Risk of genetic/familial disease

Risk of immunocompromised

Not Relevant:

Occupational risk of disease

Risk of sexually transmitted infection (STI)

Risk of drug-related disease exposure

Allergy concerns for treatment

**The patient is an older man who is undergoing radiation therapy for prostate cancer. The patient's age, vector exposure, and compromised immune system make him particularly susceptible to certain diseases. His symptoms are becoming worse, and will require treatment as soon as possible! Not all of these factors may be important to your ultimate diagnosis; however they are all pieces of information that you should consider when building a hypothesis.

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. In the beginning of your diagnostic process you should try and think broadly to help you consider any and all reasonable possibilities. You can then narrow down these possibilities by performing diagnostics that can support or refute your hypothesis.

2. Given your current information, select the best candidates for the cause of your patient's symptoms.

A form of bacterial meningitis (meningococcal, pneumococcal meningitis...etc.)

Listeriosis (CNS infection)

Arboviral encephalitis

Cryptococcosis

3. To help you better understand your patient's condition, you would like to collect some samples for analysis. You decide to take a blood sample, but you would like to take one other type of sample as well. Select the sample that will be most informative if you suspect that your patient has a disease of the central nervous system.

A CSF sample

**A CSF sample obtained via spinal tap is a critical diagnostic for any patient who is suspected of having a microbial disease of the nervous system. This type of sample can yield quick and definitive results about your patient's immune response, and the type of organism responsible for your patient's condition. You will now analyze this fluid.

Interpret your results.

Fluid analysis of your patient's CSF shows the following;

CSF Analysis	Your Patient	Normal Adult
Color of CSF	Cloudy	Clear
Opening pressure of lumbar puncture (cm H20)	29	7-18
CSF white blood cell count	500	0-5
CSF red blood cell count	None	None
% CSF leukocytes
Neutrophils	72%	None
Lymphocytes	33%	None
CSF total protein (mg/100 mL)	1.56	15-60
CSF glucose (mg/dL)	25	50-80
Blood glucose (fasted) (mg/dL)	96	70-110
Glucose ratio CSF/blood	0.26	>0.66

Note: mg/dL = milligrams per deciliter.

4. Based upon these results, which of the following can you conclude about your patient?

Your patient has a CNS infection.

Consider new evidence!

As you are considering your patient's CSF analyses, a nurse brings to your attention that two other patients have been admitted to the emergency room with similar symptoms. It turns out, both new patients are also living at the same retirement community as your patient!

5. Use this new information to help you refine your hypothesis. Are there diseases that are more likely based upon this evidence? Make sure to consider your patient's history, symptoms, and your diagnostics (and their validity) when making your case.

A form of bacterial meningitis (meningococcal, pneumococcal meningitis...etc.)

Listeriosis (CNS infection)

**All of your patients could've been exposed to bacterial meningitis or listeriosis at the retirement community. Although your original patient was at risk for arboviral encephalitis and cryptococcosis during his travel, there is no evidence to suggest that the other two patients were also exposed.

Refine your hypothesis.

Now that you have reasonable evidence suggesting that the cause of your patient's condition was acquired at his retirement community, you decide to ask your patient and the two new patients, some questions.
You find out that patients 1 and 2 know each other, and often spend time together. Patient 3 does not know either of them.

All patients live in separate areas of the community; however, they all eat meals in a common dining hall. At mealtime, the retirement community offers several food choices. The food choices of the sick patients over the last week are shown below. An "x" indicates items that a patient ate, while an "o" denotes items they did NOT eat.

Patient #	Fruit and cottage cheese	Eggs	Turkey sandwich	Vegetable soup	Chicken casserole	Spaghetti with meatballs	Side salad	Soft serve ice cream
1	x	o	x	x	x	o	x	x
2	x	x	x	o	x	o	x	x
3	x	o	x	x	o	x	x	x

6. What does this evidence show?

Your patients could have bacterial meningitis or listeriosis.

**You cannot determine if your patients have a form of bacterial meningitis or listeriosis yet. Your patients could've acquired listeriosis from the food they ate, or it is possible that bacterial meningitis was spread as an aerosol that your patients acquired through proximity to one another in the dining room.

7. Which diagnostics would you like to use?

Bacterial culture of CSF fluid

CSF Gram-stain

**You requested a Gram stain and bacterial culture of your patient's CSF, and receive the following results:

Procedure	Result
Gram-stain	Gram-positive.
Bacterial culture	Positive for colonies of bacilli. It is beta-hemolytic on blood agar.

8. What pathogen is responsible for your patient's condition?

Listeria monocytogenes

**Listeria monocytogenes is a Gram-positive bacillus (rod). It is beta-hemolytic on blood agar.

9. What diagnosis will you make for this patient?

Listeriosis meningitis

**Listeria monocytogenes is responsible for listeriosis meningitis

10. All of the patients who were diagnosed with listeriosis ate the following food items:
fruit and cottage cheese: contains cottage cheese, cantaloupe.

turkey sandwich: contains wheat bread, turkey, tomatoes, Swiss cheese.

side salad: contains iceberg lettuce, tomatoes, blue cheese dressing

soft-serve ice cream: contains ice cream.

Which could be responsible for the listeriosis outbreak?

The cottage cheese; The cantaloupe; The turkey meat; The tomatoes; The Swiss cheese; The iceberg lettuce; The blue cheese dressing; The soft-serve ice cream.

**Listeriosis can be spread through a variety of foods, including meats, vegetables, fruits, and dairy products.

11. Listeriosis is contracted through ingesting food contaminated with Listeria monocytogenes. How does this bacterium leave the gastrointestinal tract to cross the blood-brain-barrier and reach the CNS?

L. monocytogenes spreads from cell-to-cell.

**L. monocytogenes is capable of cell-to-cell transfer. This form of spread is known as paracytophagy. L. monocytogenes are able to leave the gastrointestinal tract, and/or cross the blood-brain-barrier through this sort of intracellular spread.

12. How will you treat your patients?

Penicillin G

**You administer penicillin G to your patients. All patients begin to recover. You have successfully treated the disease!

Big Picture Coaching Activity: Neglected Tropical Disease

This case study introduces the student to neglected tropical diseases (NTD). It begins with an individual who is experiencing an infection with a tropical disease. Students will be asked to identify the causative agent and then answer additional questions about vectors, treatments, and the benefits of water sanitization. The final question will be a binning activity.

Read through the Big Picture: Neglected Tropical Diseases feature, and then complete the activity and questions below.

1. Whitney went on a mission trip to Africa with her church group. They visited for two weeks and worked with doctors in the area to provide information about tropical diseases and the availability of treatment and vaccines. About a month after returning home, she started having headaches, fever, and severe joint pain. She went to the doctor and was diagnosed with African sleeping sickness. What is the causative agent of this disease?

Trypanosoma brucei

**Trypanosoma brucei is the causative agent of African sleeping sickness. The organism is a protozoan, eukaryotic, flagellated, and has an undulating membrane. An infected individual will initially show general signs of illness, such as fever, malaise, headaches, and joint pain. Progression of the illness occurs when the organism parasitizes the central nervous system. Coma and death can occur if left untreated.

2. The Big Picture Activity mentions multiple strategies for reducing the incidence of NTD. Which of the following would you recommend as a successful strategy for preventing the transmission of African sleeping sickness?

preventing contact with insects such as mosquitoes, kissing bugs, fleas, etc., through the use of chemicals

**Prevention of African sleeping sickness requires limiting the disease reservoir and avoiding the vector that transmits Trypanosoma. It is difficult to reduce the reservoir, so the BEST choice is vector control. Pesticide use can reduce vector populations and reduce the incidence of infection.

3. As mentioned previously, African sleeping sickness is transmitted via a biological vector. Which of the following vectors is responsible for transmitting Trypanosoma brucei?

tsetse fly

**Tsetse flies are responsible for transmitting Trypanosoma brucei to humans. The flies obtain the parasite when drinking a blood meal from an infected human. Once in the fly, the parasite goes to the midgut to replicate via binary fission and transform into an epimastigote (developmental stage in Trypanosoma). The epimastigotes travel to the salivary glands and are then introduced to the next host when the fly feeds on another blood meal. Prevention relies on minimizing the chances of being bitten by the tsetse fly. Traps, insect repellants, and other pesticides are effective.

4. Improved water sanitation and hygiene services are listed in the Big Picture activity as a method of prevention for NTDs. Why is water sanitation a possible method of prevention?

The ability to bathe in clean water can help in the reduction of disease transmission.

**Water sanitation and improved hygiene services allow individuals to bathe in water that has not been contaminated. This helps to prevent the transmission of disease because multiple people are not bathing in the same water and there is less chance of contamination.

5. Treatment for an NTD will depend on whether it is caused by a prokaryote or a eukaryote. In this section, place each organism in the appropriate bin.

Prokaryote: Mycobacterium ulcerans and Chlamydia trachomatis

Eukaryote: Onchocerca volvulus and Typanosoma cruzi

Neither: Dengue virus and Rabies virus

**Mycobacterium ulcerans and Chlamydia trachomatis are both bacteria that cause NTDs. They are prokaryotic in nature and would be treated with antibiotics. Onchocerca volvulus is a helminth that causes onchocerciasis, is eukaryotic, and would be treated with an anti-parasitic. Trypanosoma cruzi is a protozoan that causes Chagas Disease, is eukaryotic, and would be treated with an anti-protozoan. Dengue and Rabies are both viruses that cause NTDs, but are not classified as prokaryotic or eukaryotic. They would be treated with anti-virals.