Infectious disease Answers 1
Meysam Amiri 27/01/2011
pm
:Please enter your Name
Refrence: Med.Science Laboratories Journal
Soon! Infectious Disease Questions 1
Infectious Disease
Questions
DIRECTIONS: Each item below contains a question or incomplete statement followed by suggested responses. Select the one best response to each question.
1. A 30-year-old male patient complains of fever and sore throat for several days. The patient presents to you today with additional complaints of hoarseness, difficulty breathing, and drooling. On examination, the patient is febrile and has inspiratory stridor. Which of the following is the best course of action?
a. Begin outpatient treatment with ampicillin
b. Culture throat for β-hemolytic streptococci
c. Admit to intensive care unit and obtain otolaryngology consultation
d. Schedule for chest x-ray
2. A 70-year-old patient with long-standing type 2 diabetes mellitus pre-
sents with complaints of pain in the left ear with purulent drainage. On
physical exam, the patient is afebrile. The pinna of the left ear is tender, and
the external auditory canal is swollen and edematous. The peripheral white
blood cell count is normal. The organism most likely to grow from the puru-
lent drainage is
a. Pseudomonas aeruginosa
b. Staphylococcus aureus
c. Candida albicans
d. Haemophilus influenzae
e. Moraxella catarrhalis
Items 3-4
A 25-year-old male student presents with the chief complaint of rash. There is no headache, fever, or myalgia. A slightly pruritic maculopapular rash is noted over the abdomen, trunk, palms of the hands, and soles of the feet. Inguinal, occipital, and cervical lymphadenopathy is also noted. Hypertrophic, flat, wartlike lesions are noted around the anal area. Laboratory studies show the following:
Hct: 40%
Hgb: 14 g/dL
WBC: 13,000/µL
Diff:
Segmented neutrophils: 50%
Lymphocytes: 50%
3. The most useful laboratory test in this patient is
a. Weil-Felix titer
b. Venereal Disease Research Laboratory (VDRL) test
c. Chlamydia titer
d. Blood cultures
4. The treatment of choice for this patient is
a. Penicillin
b. Ceftriaxone
c. Tetracycline
d. Interferon α
e. Erythromycin
Items 5-7
A 20-year-old female college student presents with a 5-day history of cough, low-grade fever (temperature 100°F), sore throat, and coryza. On exam, there is mild conjunctivitis and pharyngitis. Tympanic membranes are inflamed, and one bullous lesion is seen. Chest exam shows few basilar rales. Laboratory findings are as follows:
Hct: 38
WBC: 12,000/µL
Lymphocytes: 50%
Mean corpuscular volume (MCV): 83 nL Reticulocytes: 3% of red cells
CXR: bilateral patchy lower lobe infiltrates
5. The sputum Gram stain is likely to show
a. Gram-positive diplococci
b. Tiny gram-negative coccobacilli
c. White blood cells without organisms
d. Acid-fast bacilli
6. This patient is likely to have
a. High titers of adenovirus
b. High titers of IgM cold agglutinins
c. A positive silver methenamine stain
d. A positive blood culture for Streptococcus pneumoniae
7. Treatment of choice is
a. Erythromycin
b. Supportive therapy
c. Trimethoprim-sulfamethoxazole
d. Cefuroxime
Items 8-10
A 19-year-old male presents with a 1-week history of malaise and anorexia
followed by fever and sore throat. On physical examination, the throat is
inflamed without exudate. There are a few palatal petechiae. Cervical
adenopathy is present. The liver is percussed at 12 cm and the spleen is
palpable.
Throat culture: negative for group A streptococci Hct: 38%
Hgb: 12 g/dL
Reticulocytes: 4%
WBC: 14,000/µL
Segmented: 30%
Lymphocytes: 60%
Monocytes: 10%
Bilirubin total: 2.0 mg/dL (normal 0.2 to 1.2)
Lactic dehydrogenase (LDH) serum: 260 IU/L (normal 20 to 220) Aspartate (AST): 40 U/L (normal 8 to 20 U/L)
Alanine (ALT): 35 U/L (normal 8 to 20 U/L)
Alkaline phosphatase: 40 IU/L (normal 35 to 125)
8. The most important initial test is
a. Liver biopsy
b. Strep screen
c. Peripheral blood smear
d. Toxoplasmosis IgG
e. Lymph node biopsy
9. The most important serum test is
a. Heterophile antibody
b. Hepatitis B IgM
c. Cytomegalovirus IgG
d. ASLO titer
e. Hepatitis C antibody
10. Corticosteroids would be indicated if
a. Liver function tests worsen
b. Fatigue lasts more than 1 week
c. Severe hemolytic anemia is demonstrated
d. Hepatitis B is confirmed
DIRECTIONS: Each group of questions below consists of lettered
options followed by a set of numbered items. For each numbered item,
select the one lettered option with which it is most closely associated. Each
lettered option may be used once, more than once, or not at all.
Items 11-14
Match the clinical description with the most likely organism.
a. Streptococcus pneumoniae
b. Staphylococcus aureus
c. Viridans streptococci
d. Providencia stuartii
e. Actinomyces israelii
f. Haemophilus ducreyi
g. Neisseria meningitidis
h. Listeria monocytogenes
11. A 30-year-old female with mitral valve prolapse and mitral regurgitant murmur develops fever, weight loss, and anorexia after undergoing a dental procedure. (CHOOSE 1 ORGANISM)
12. An 80-year-old-male, hospitalized for hip fracture, has a Foley
catheter in place when he develops shaking chills, fever, and hypotension.
(CHOOSE 1 ORGANISM)
13. A young man develops a painless, fluctuant purplish lesion over the mandible. Cutaneous fistula is noted after several weeks. (CHOOSE 1 ORGANISM)
14. A sickle cell anemia patient presents with high fever, toxicity, signs of pneumonia, and stiff neck. (CHOOSE 1 ORGANISM)
Items 15-18
Select an antiviral agent for each patient.
a. Ganciclovir
b. Acyclovir
c. Interferon α
d. Didanosine
e. Ribavirin
f. Amantadine
g. Vidarabine
h. Zalcitabine
15. A military recruit develops pneumonia secondary to influenza A. Symptoms began 24 h prior to physician visit. (SELECT 1 AGENT)
16. An HIV-positive patient with a CD4 count of 50 complains of the onset of visual blurring; opacity is seen on funduscopic exam. (SELECT 1 AGENT)
17. A sexually active young woman has anogenital warts and requests intralesional therapy. (SELECT 1 AGENT)
18. An infant with respiratory syncytial virus infection requires mechanical ventilation. (SELECT 1 AGENT)
Items 19-21
Select the fungal agent most likely responsible for the disease process described.
a. Histoplasma capsulatum
b. Blastomycosis dermatitidis
c. Coccidioides immitis
d. Cryptococcus neoformans
e. Candida albicans
f. Aspergillus fumigatus
g. Zygomycosis
19. A young, previously healthy male presents with verrucous skin lesions, bone pain, fever, cough, and weight loss. Chest x-ray shows nodular infiltrates. (SELECT 1 AGENT)
20. A diabetic patient is admitted with elevated blood sugar and acidosis. The patient complains of headache and sinus tenderness and has black, necrotic material draining from the nares. (SELECT 1 AGENT)
21. A young woman presents with asthma and eosinophilia. Fleeting pul-
monary infiltrates occur with bronchial plugging. (SELECT 1 AGENT)
Items 22-24
A 40-year-old male develops bilateral facial weakness after returning from
a camping trip in Wisconsin that lasted 6 weeks. The patient gives a history
of arthralgias. On exam, he cannot close either eye well or raise either eye-
brow. The first heart sound is diminished. There is no evidence of arthritis.
Hgb: 14 g /dL
WBC: 10,000/µL
VDRL: negative
FTA-Abs: positive
ECG: first-degree AV block
22. Which of the following would be most useful?
a. CT scan of head
b. MRI of head
c. More detailed history
d. Kveim test
23. The likely cause of these symptoms is
a. Intracranial infection
b. Lyme disease
c. Endocarditis
d. Herpes simplex
Treatment of choice is .24
a. Penicillin or ceftriaxone
b. Acyclovir
c. Corticosteroids
d. Aminoglycoside
?? soon> For Receive
virus 4
virus 4
Latency
Inapparent infections (those that do not cause specific signs and symptoms) often result after exposure to picornaviruses, influenza viruses, rhinoviruses, herpesviruses, and adenoviruses but less frequently to measles and chickenpox viruses. In cases of inapparent infection, long-lasting immunity develops, but only to the strain of virus that has the same antigenic composition as the original infecting virus.
Certain of these viruses persist in the tissues of the host after the initial infection despite the presence of circulating antibodies to it in the blood and tissues. Such viruses probably reside inside cells, where they are protected from antibodies that cannot penetrate the cell membrane. Among persistent viruses are adenoviruses, measles virus, and, in particular, many kinds of herpesviruses. The genetic information of herpesviruses and adenoviruses can be integrated into the genome of the host cell, but it is believed that these viruses frequently, and the measles virus invariably, reside in cells in the form of extrachromosomal genes (genes not integrated in chromosomes). These dormant viruses can be activated by many factors, such as trauma, another infection, emotional stress, menstruation, excessive exposure to sunlight, and various illnesses.
The phenomenon of latency and reactivation is particularly common among viruses of the family Herpesviridae, which cause chronic or recurrent diseases: (1) herpes simplex virus type 1, which causes recurrent cold sores, (2) herpes simplex virus type 2 in genital tissue, which causes repeated herpetic infections of the vagina or penis, (3) cytomegalovirus, which usually produces an inapparent infection activated by simultaneously occurring disease to cause severe liver, lung, or nervous-system disease, and (4) varicella virus, which is the causative agent of chickenpox but which can be activated decades later to produce herpes zoster (shingles). A rare, but invariably fatal, disease of the nervous system is subacute sclerosing panencephalitis (SSPE), which is a progressive, degenerative condition caused by measles virus (a paramyxovirus) lying dormant in brain cells for many years and then reactivated, usually in adolescence. There is no simple explanation for why latent viruses, such as those in the family Herpesviridae, that are present in the tissues of most adult humans can be activated to cause disease in some people but not in others.
virus 3
Viral DNA integration
Lysogeny
Many bacterial and animal viruses lie dormant in the infected cell, and their DNA may be integrated into the DNA of the host cell chromosome. The integrated viral DNA replicates as the cell genome replicates; after cell division, the integrated viral DNA is duplicated and usually distributed equally to the two cells that result. The bacteria that carry the noninfective precursor phage, called the prophage, remain healthy and continue to grow until they are stimulated by some perturbing factor, such as ultraviolet light. The prophage DNA is then excised from the bacterial chromosome, and the phage replicates, producing many progeny phages and lysing the host bacterial cell. This process, originally discovered in temperate bacteriophages in 1950 by the French microbiologist André Lwoff, is called lysogeny.
The classic example of a temperate bacteriophage is called lambda (λ) virus, which readily causes lysogeny in certain species of the bacterium Escherichia coli. The DNA of the λ bacteriophage is integrated into the DNA of the E. coli host chromosome at specific regions called attachment sites. The integrated prophage is the inherited, noninfectious form of the virus; it contains a gene that represses the lytic functions of the phage and thus assures that the host cell will continue to replicate the phage DNA along with its own and that it will not be destroyed by the virus. Ultraviolet light, or other factors that stimulate the replication of DNA in the host cell, causes the formation of a recA protease, an enzyme that breaks apart the λ phage repressor and induces λ phage replication and, eventually, destruction of the host cell.
Excision of the prophage DNA from the host chromosomal DNA (as an initial step in the synthesis of an infective, lytic virus) sometimes results in the removal of some of the host cell DNA, which is packaged into defective bacteriophages; part of the bacteriophage DNA is removed and replaced at the other end by a gene of the host bacterium. Such a virus particle is called a transducing phage because, when it infects a bacterial cell, it can transmit the gene captured by λ phage DNA into the next bacterial cell it infects. Transduction by bacteriophages is an efficient means for transferring the genetic information of one bacterial cell to another.
This means of transferring genetic information, called lysogenic conversion, imparts genes with special functions to bacterial cells without such functions. It is common in bacteria and is an important aspect of the epidemiology (incidence, distribution, and control) of infectious diseases. For example, the bacterium Corynebacterium diphtheriae is the causative agent of diphtheria, but only when it contains the prophage of bacteriophage β, which codes for the toxin that is responsible for the disease.
Malignant transformation
A phenomenon analogous to bacterial cell lysogeny occurs in animal cells infected with certain viruses. These animal viruses do not generally cause disease immediately for certain animal cells. Instead, animal cells are persistently infected with such viruses, the DNA of which (provirus) is integrated into the chromosomal DNA of the host cell. In general, cells with integrated proviral DNA are converted into cancer cells, a phenomenon known as malignant transformation. As is the case with bacterial prophages, the transformed animal cell contains no infectious virus but only the integrated provirus DNA, which replicates along with the dividing cell's chromosomes. Therefore, following mitosis of the transformed cell, each new cell receives a copy of the proviral DNA. The hallmark of these transformed animal cells is that their growth is uncontrollable; unlike normal cells, their growth is not inhibited by contact with other cells, and they lose their capacity to adhere (anchor) to certain surfaces. Growth of normal tissues and organs is also controlled by a genetic phenomenon called programmed cell death, or apoptosis, in which a certain number of cells will die and be eliminated after a finite number of divisions. Malignant transformation can impede programmed cell death, thus allowing the cells to grow uncontrolled, resulting in cancer.
Among the animal viruses that cause malignant transformation by integration of proviral DNA are several families of DNA viruses and one large family of RNA viruses, the Retroviridae. Viruses of the family Papovaviridae were perhaps the first to be associated with malignancy (causing death or illness) in animals. Polyomavirus is widespread in mice; it can infect other rodents, and it can cause tumours in infected animals. Another virus of the family Papovaviridae is simian virus 40 (SV40), originally isolated from cells of the African green monkey (Cercopithecus sabaeus), where it grows rapidly and kills the cells. Infection of rodent or human cells, however, results in an abortive infection (an incompatibility between the virus and the host cell) but sometimes induces malignancy (sarcomas or lymphomas) in the occasional cell that is transformed. Viruses related to polyomavirus and SV40 have been isolated from humans, one of which, the JC virus, appears to be the causative agent of a fatal neurological disease called progressive multifocal leukoencephalopathy. In general, however, the human papovaviruses are not clearly associated with disease.
Other viruses of the family Papovaviridae include the papillomaviruses, which are also small polygonal viruses containing circular double-stranded DNA. The papillomaviruses are associated with usually benign (nonthreatening) but widespread tumours, called papillomas or polyps, occurring in human skin and the genital tract. Specific papillomaviruses have been identified in humans in common warts and in genital warts (condylomata acuminata). Cancers of the human genital tract, particularly uterine cancer of the cervix, are frequently found in association with human papillomavirus type 16 (HPV 16); the virus undoubtedly is transmitted as a venereal disease.
SOON??!?
Infectious Disease
Questions
Answers, Explanations, and References
virus 2
virus 2
By far the best-studied example of a helical rod-shaped virus is the tobacco mosaic virus, which was crystallized by Wendell Stanley in 1935. The tobacco mosaic virus contains a genome of single-stranded RNA encased by 2,130 molecules of a single protein; there are 161/3 protein molecules for each turn of the RNA helix in the ratio of three nucleotides for each protein molecule.
Under the right environmental conditions, viral RNA and protein molecules in liquid suspension will assemble themselves into a perfectly formed and fully infectious virus. The length of the helical virus capsid is determined by the length of the nucleic acid molecule, which is the framework for the assembly of the capsid protein. The various helical viruses have different lengths and widths depending on the size of the nucleic acid as well as on the mass and shape of the protein molecule. Some of these helical viruses form rigid rods, while others form flexible rods, depending on the properties of the assembled proteins.