Chapter17: INTESTINES:Infectious Enterocolitis Flashcards

Question

What explalins the enteric fever in Campylobacter jejuni?

Answer 1

Enteric fever occurs **when bacteria proliferate within the lamina propria and mesenteric lymph nodes.**

Answer 2

reactive arthiritis

Answer 3

Other extra-intestinal complications, including : * erythema nodosum and * Guillain-Barré syndrome, * a flaccid paralysis caused by autoimmune-induced inflammation of peripheral nerves, are not HLA-linked. [62]

Answer 4

**Molecular mimicry** has been implicated in the pathogenesis of Guillain-Barré syndrome, as **serum antibodies to C. jejuni lipopolysaccharide cross-react with peripheral and central nervous system gangliosides.** Moreover, 15% to 50% of individuals with Guillain-Barré syndrome have **positive stool cultures or circulating antibodies to Campylobacter**. [63] Fortunately, Guillain-Barré syndrome develops in **0.1% or less of those infected with Campylobacter**

Answer 5

* **comma-shaped,** * **flagellated,** * **Gram-negative organisms.**

Answer 6

Diagnosis is primarily by **stool culture**, since **biopsy findings are *_nonspecific, and reveal acute self-limited colitis with features common to many forms of infectious colitis_***. [64]

Answer 7

Mucosal and intraepithelial neutrophil infiltrates are prominent, particularly within the superficial mucosa ( Fig. 17-28A ); **cryptitis** (neutrophil infiltration of the crypts) and **crypt abscesses** (crypts with accumulations of luminal neutrophils) may also be present. Importantly, crypt architecture is preserved ( Fig. 17-28D ), although this can be difficult to assess in cases with severe mucosal damage.

Answer 8

FIGURE 17-28 Bacterial enterocolitis. * A, Campylobacter jejuni infection produces **acute, self-limited colitis.** Neutrophils can be seen within surface and crypt epithelium and a crypt abscess is present at the lower right. * B, In Yersinia infection the surface epithelium can be eroded by neutrophils and the lamina propria is densely infiltrated by sheets of plasma cells admixed with lymphocytes and neutrophils. * C, Enterohemorrhagic E. coli O157:H7 results in an ischemia-like morphology with surface atrophy and erosion. * D, Enteroinvasive * E. coli infection is a similar to other acute, self-limited colitides. Note the maintenance of * normal crypt architecture and spacing, despite abundant intraepithelial neutrophils.

Answer 9

Ingestion of as few as **500** C. jejuni organisms can cause disease **after an incubation period of up to 8 days.** **Watery diarrhea, either acute or following an influenza-like prodrome, is the primary symptom, and dysentery develops in 15% of patients.** Patients may shed bacteria for 1 month or more after clinical resolution. Antibiotic therapy is generally not required.

Answer 10

Shigella are **Gram-negative bacilli** that were initially isolated during the Japanese red diarrhea epidemic of 1897. Four major strains are now recognized. Shigella are **unencapsulated,** **nonmotile**, **facultative anaerobes** that belong to the **Enterobacteriaceae** and are **closely related to enteroinvasive E. coli**.

Answer 11

Although **humans are the only known reservoir,** Shigella spp. remain **one of the most common causes of bloody diarrhea.** It is estimated that 165 million cases occur worldwide each year. [65] Given the infective dose of fewer than several hundred organisms and the presence of as many as 10 9 organisms in each gram of stool during acute disease,

Answer 12

Shigella are **highly transmissible by the fecal-oral route** or **via contaminated water and food.**

Answer 13

In the United States and Europe, children in daycare centers, migrant workers, travelers to developing countries, and those in nursing homes are most commonly affected. [66,] [67] Most Shigella infections and deaths occur in children under 5 years of age, and in countries where Shigella is endemic it is responsible for approximately 10% of all pediatric diarrheal disease and as many as 75% of diarrheal deaths.

Answer 14

Shigella are **resistant to the harsh acidic environment of the stomach**, which **translates into an extremely low infective dose**. Once in the intestine, **organisms are taken up by M, or microfold,** epithelial cells, which are specialized for sampling and presentation of luminal antigens. Shigella **proliferate intracellularly, escape into the lamina propria, and are phagocytosed by macrophages,**in which they**induce apoptosis**. The **ensuing inflammatory process** **damages surface epithelia and allows Shigella**within the intestinal lumen to gain access to the colonocyte basolateral membrane, which is the only surface through which infection can occur in epithelial cells **(other than M cells**). All Shigella spp. carry **virulence plasmids**, some of which encode a **type III secretion system** capable of directly injecting bacterial proteins into the host cytoplasm. **S. dysenteriae serotype 1** also release the **Shiga toxin Stx,** which **inhibits eukaryotic protein synthesis resulting in host cell damage and death**

Answer 15

**S. dysenteriae serotype 1** also release the Shiga toxin **Stx,** which inhibits eukaryotic protein synthesis resulting in host cell damage and death

Answer 16

Shigella infections are **most prominent in the left colon**, but the **ileum may also be involved**, perhaps **reflecting the abundance of M cells in the dome epithelium over the Peyer's patche**s.

Answer 17

The **mucosa is hemorrhagic and ulcerated**, and **pseudomembranes may be present.** The histology of early cases is similar to other acute self-limited colitides, such as Campylobacter colitis, but because of the **tropism for M cells, aphthous-appearing ulcers similar to those seen in Crohn disease may occur**. The potential for confusion with chronic inflammatory bowel disease is significant, particularly if there is distortion of crypt architecture.

Answer 18

* **incubation period of as long as 4 days**, Shigella * causes **self-limited disease** * characterized by about **6 days of diarrhea, fever, and abdominal pain.** * The initially watery diarrhea progresses to a dysenteric phase in approximately 50% of patients, and constitutional symptoms can persist for as long as 1 month. * The subacute presentation that develops in a minority of adults is characterized by several weeks of waxing and waning diarrhea that can mimic new-onset ulcerative colitis. [68] * While duration is typically shorter in children, severity is often much greater. Confirmation of Shigella infection requires stool culture.

Answer 19

The potential for confusion with chronic inflammatory bowel disease is significant, particularly **if there is distortion of crypt architecture.**

Answer 20

Complications of Shigella infection are uncommon and include : * Reiter syndrome, * a triad of sterile **arthritis, urethritis, and conjunctivitis** that preferentially affects HLA-B27-positive men between 20 and 40 years of age. * Hemolytic-uremic syndrome, which is typically **associated with enterohemorrhagic E. coli (EHEC),** may also occur after infection with S. dysenteriae **serotype 1 that secrete Shiga toxin** [69] [70] [71] ; **only Shigella organisms that secrete the toxin are associated with hemolytic-uremic syndrome** ( Chapter 20 ). *

Answer 21

which is **typically associated with enterohemorrhagic E. coli (EHEC)**, ***_may also occur after infection with S. dysenteriae serotype 1 that secrete Shiga toxin_*** [69] [70] [71] ; ***_only Shigella organisms that secrete the toxin are associated with hemolytic-uremic syndrom_***e ( Chapter 20 ).

Answer 22

Antibiotic treatment shortens the clinical course and reduces the duration over which organisms are shed in the stool, but **antidiarrheal medications are contraindicated because they can prolong symptoms and delay Shigella clearance.**

Answer 23

Salmonella, which are classified within the **Enterobacteriaceae** family of **Gram-negative bacilli,** are divided into **Salmonella typhi**, the causative agent of **typhoid fever (**discussed in the next section) and **nontyphoid Salmonella**. Nontyphoid Salmonella infection is usually due to S. enteritidis; more than 1 million cases occur each year in the United States, and the prevalence is even greater in other countries. Infection is **most common in young children** and the **elderly, with peak incidence** in summer and fall.

Answer 24

Transmission is usually through **contaminated food,** particularly **raw or undercooked meat, poultry, eggs, and milk.**

Answer 25

**Very few viable Salmonella** are **necessary to cause infection**, and the **absence of gastric acid, as in individuals with atrophic gastritis**or those on**acid-suppressive therapy, further reduces the required inoculum.** Salmonella possess virulence genes that encode a type III secretion system capable of transferring bacterial proteins into M cells and enterocytes. The transferred proteins activate host cell Rho GTPases, thereby triggering actin rearrangement and bacterial uptake that allow bacterial growth within phagosomes. In addition, **flagellin,** the core protein of bacterial flagellae, activates TLR5 on host cells and increases the local inflammatory response. [72] Similarly, bacterial lipopolysaccharide activates TLR4, although some Salmonella strains express a virulence factor that prevents TLR4 activation from occurring. Salmonella also secrete a molecule that induces epithelial release of the eicosanoid hepoxilin A3, thereby drawing neutrophils into the intestinal lumen and potentiating mucosal damage. [73] Mucosal TH17 immune responses limit infection to the colon.

Answer 26

Morphology. The gross and microscopic features of Salmonella enteritis are non-specific and are similar to the acute self-limited colitis of Campylobacter and Shigella. **Stool cultures are essential for diagnosis**

Answer 27

Salmonella infections are **clinically indistinguishable** from those **caused by other enteric pathogens,** and symptoms range from **loose stools to cholera-like** profuse diarrhea to dysentery. Fever often **resolves within 2 days,** but diarrhea can persist for a week and organisms can be shed in the stool for several weeks after resolution.

Answer 28

Antibiotic therapy is not recommended in most cases, **because it can prolong the carrier state** or **even cause relapse and does not typically shorten the duration of diarrhea**. [74] Most Salmonella infections are selflimited, but deaths do occur. The risk of severe illness and complications is increased in patients with malignancies, immunosuppression, alcoholism, cardiovascular dysfunction, sickle cell disease, and hemolytic anemia

Answer 29

Typhoid fever, also referred to as enteric fever , is caused by **Salmonella typhi and Salmonella** **paratyphi**. It affects up to 30 million individuals worldwide each year. The majority of cases in endemic countries are due to S. typhi, while infection by **S. paratyphi is more common among travelers, [**75] perhaps**because travelers tend to be vaccinated against S. typhi** (there are no effective S. paratyphi vaccines).

Answer 30

The majority of cases in endemic countries are due to S. typhi, while infection by **S. paratyphi is more common among travelers,**[75] perhaps**because travelers tend to be vaccinated against S. typhi (there are no effective S. paratyphi vaccines).**

Answer 31

In endemic areas children and adolescents are **affected most often,** but there is **no age preference in developed countries.** Infection is **strongly associated with travel to India, Mexico, the Philippines, Pakistan, El Salvador, and Haiti. [76]**

Answer 32

Like Shigell**a, humans are the sole reservoir for S. typhi** and S. paratyphi and transmission occurs from **person to person or via food or contaminated water**. Gallbladder colonization with S. typhi or S. paratyphi may be associated with gallstones and the chronic carrier state

Answer 33

S. typhi are **able to survive in gastric acid** and, once in the small intestine, are **taken up by and invade M cells.** Organisms are then engulfed by mononuclear cells in the underlying lymphoid tissue. Unlike S. enteritidis, S. typhi can then disseminate via lymphatic and blood vessels. This causes reactive hyperplasia of phagocytes and lymphoid tissues throughout the body

Answer 34

Infection causes Peyer's patches in the terminal ileum to enlarge into **sharply delineated, plateau-like** elevations up to 8 cm in diameter. Draining mesenteric lymph nodes are also enlarged. Neutrophils accumulate within the superficial lamina propria, and macrophages containing bacteria, red blood cells, and nuclear debris mix with lymphocytes and plasma cells in the lamina propria. Mucosal shedding creates **oval ulcers, oriented along the axis of the ileum, that may perforate.** The draining lymph nodes also harbor organisms and are enlarged due to phagocyte accumulation. The spleen is enlarged and soft, with uniformly pale red pulp, obliterated follicular markings, and prominent phagocyte hyperplasia. The **liver shows small, randomly scattered foci** of parenchymal necrosis in which hepatocytes are replaced by macrophage aggregates, called **typhoid nodules**, that may also develop in the bone marrow and lymph nodes

Answer 35

Patients experience anorexia, abdominal pain, bloating, nausea, vomiting, and bloody diarrhea followed by a short asymptomatic phase that gives way to bacteremia and fever with flu-like symptoms. [77] Blood cultures are positive in more than 90% of affected individuals during the febrile phase, which may prompt antibiotic treatment and prevent further disease progression. [76] In patients who do not receive treatment the febrile phase is followed by up to 2 weeks of sustained high fevers and abdominal tenderness that may mimic appendicitis. Rose spots, small erythematous maculopapular lesions, are seen on the chest and abdomen. [77] Symptoms abate after several weeks in those who survive, although relapse can occur. [77] Systemic dissemination may cause extra-intestinal complications including encephalopathy, meningitis, seizures, endocarditis, myocarditis, pneumonia, and cholecystitis. Patients with sickle cell disease are particularly susceptible to ***_Salmonella osteomyelitis_***

Answer 36

* **Y. enterocolitica and** * **Y. pseudotuberculosis** * **Y. pestis**, the agent of pulmonic and bubonic plague.

Answer 37

GI Yersinia infections are more common in Europe than North America and are most frequently linked to ingestion of pork, raw milk, and contaminated water.

Answer 38

**Y. enterocolitica** is far more common than Y. pseudotuberculosis, and infections tend to cluster in the winter, possibly related to inadequately cooked foods served at holiday gatherings.

Answer 39

Yersinia **invade M cells** and **use bacterial adhesion** proteins, adhesins, to **bind to host cell β1 integrins.** A pathogenicity island encodes an **iron uptake system that mediates iron capture and transport;**similar iron transport systems**are also present in E. coli, Klebsiella, Salmonella**, and **enterobacteria**. In **Yersinia, iron enhances virulence and stimulates** **systemic dissemination,** explaining **why individuals with hemolytic anemia or hemochromatosis are more likely to develop sepsis and are at greater risk of death.**

Answer 40

In **Yersinia, iron enhances virulence and stimulates systemic dissemination,** explaining why individuals with hemolytic anemia or hemochromatosis are more likely to develop sepsis and are at greater risk of death.

Answer 41

**ileum, appendix, and right colon** ( Fig. 17-28B ).

Answer 42

The organisms multiply **extracellularly in lymphoid tissue,** resulting in *_**regional lymph node and Peyer's patch hyperplasia**_* and bowel wall thickening. [79] The mucosa overlying lymphoid tissue may become hemorrhagic, and aphthous-appearing ulcers may develop, along with neutrophil infiltrates (see Fig. 17-28B ) and **granulomas**, **increasing the potential for diagnostic confusion with Crohn disease.**

Answer 43

The mucosa overlying **lymphoid tissue may become hemorrhagic**, and **aphthous-appearing ulcer**s may develop, along with **neutrophil infiltrates** (see Fig. 17-28B ) and ***_granulomas,_*** increasing the potential for diagnostic confusion with Crohn disease.

Answer 44

Clinical Features. People infected with Yersinia **generally present with abdominal pain, but fever and diarrhea may also occur.** **Nausea, vomiting, and abdominal tenderness are commo**n, and *_**Peyer's patch invasion with subsequent involvement of regional lymphatics can mimic acute appendicitis**_*in ***_teenagers and young adults_***. **Enteritis and colitis predominate in younger children.** Extraintestinal symptoms of **pharyngitis, arthralgia, and erythema nodosum** occur frequently.

Answer 45

Yersinia can be detected **in stool cultures** on Yersinia-selective agar or, in cases with **extraintestinal disease, cultures of lymph nodes or blood**. [80]

Answer 46

* **sterile arthritis,** * **Reiter syndrome,** * **myocarditis,** * **glomerulonephritis, and** * **thyroiditis**,

Answer 47

* Gram-negative bacilli that * colonize the healthy GI tract; * most are nonpathogeneic, but a subset cause human disease

Answer 48

* morphology, * mechanism of pathogenesis, and in * vitro behavior.

Answer 49

* enterotoxigenic E. coli (ETEC), * enterohemorrhagic E. coli (EHEC), * enteroinvasive E. coli (EIEC), and * enteroaggregative E. coli (EAEC).

Answer 50

Enterotoxigenic E. Coli. ETEC organisms are the ***_principal cause of traveler's diarrhea_*** and **spread via contaminated food or water**

Answer 51

Infection is common in **underdeveloped regions**, and **children younger than 2 years of age**are particularly susceptible.

Answer 52

* heat-labile toxin (LT) and * heat-stable toxin (ST) * LT toxin

Answer 53

both induce chloride and water secretion while inhibiting intestinal fluid absorption.

Answer 54

The LT toxin is similar to cholera toxin and **activates adenylate cyclase,** **resulting in increased intracellular cAMP**. This **stimulates chloride secretio**n and, **simultaneously, inhibits absorption.** **ST toxins**, which have homology to the mammalian regulatory protein guanylin**, bind to guanylate cyclase and increase intracellular cGMP** with resulting effects on transport that are similar to those produced by LT.

Answer 55

Like cholera, the histopathology induced by ETEC infection is limited.

Answer 56

* secretory, * noninflammatory diarrhea, d * ehydration, and, in severe cases, shock.

Answer 57

**Enterohemorrhagic E. Coli.** * E. coli O157:H7 and * non-O157:H7 serotypes.

Answer 58

consumption of inadequately cooked ground beef, sometimes from fast-food establishments. Contaminated milk and vegetables are also vehicles for infection.

Answer 59

**Shiga-like toxins**, and the morphology (see Fig. 17-28C ) and clinical symptoms are thus similar to S. dysenteriae.

Answer 60

**O157:H7 strains of EHEC** are more likely than non-O157:H7 serotypes to cause large outbreaks, **bloody diarrhea, and hemolytic-uremic syndrome.**

Answer 61

Both O157:H7 and non-O157:H7 serotypes ***_produce Shiga-like toxins_***, and the morphology (see Fig. 17-28C ) and clinical symptoms are thus similar to S. dysenteriae.

Answer 62

Enteroinvasive E. Coli. EIEC organisms are **bacteriologically similar to Shigella** and are **transmitted via food, water, or by person-to-person contact.** While EIEC **do not produce toxins**, ***_they invade epithelial cells and cause nonspecific features of acute self-limited colitis_*** (see Fig. 17-28D ). EIEC infections are **most common among young children** in developing countries and are occasionally associated with outbreaks in developed countries

Answer 63

Enteroaggregative E. Coli. EAEC organisms were identified on the **basis of their unique pattern of adherence to epithelial** **cells.** These organisms are now recognized as a **cause of diarrhea in children and adults in developed as well as developing countries.** These **can also be a cause of traveler's** **diarrhea.** [81]

Answer 64

EAEC **attach to enterocytes via adherence fimbriae** and **are aided by dispersin**, a bacterial surface protein that **neutralizes the negative surface charge of lipopolysaccharide.** While the bacteria **do produce enterotoxins related to Shigella enterotoxin and ETEC ST toxin,** **histologic damage is minimal** and the **characteristic adherence lesions are only visible by electron microscopy.** [82] EAEC organisms **cause nonbloody diarrhea** that may be prolonged in individuals **with the acquired immunodeficiency syndrome (AIDS).**

Answer 65

Clostridium difficile, is also known as antibioticassociated colitis or antibiotic-associated diarrhea. The latter terms **apply to diarrhea developing during or after a course of antibiotic therapy and may be due to C. difficile** as well as ***_Salmonella, C. perfringens type A, or Staphylococcus aureus._*** The latter two organisms produce enterotoxins and are common agents of food poisoning.

Answer 66

It is likely that **disruption of the normal colonic flora by antibiotics *_allows C. difficile overgrowth._*** Although **almost any antibiotic may be responsible, *_third-generation cephalosporins are implicated most frequently._*** **Immunosuppression is also a predisposing factor for C. difficile colitis.** Toxins released by C. difficile *_**cause the ribosylation of small GTPases, such as Rho, and lead to disruption of the epithelial cytoskeleton, tight junction barrier loss, cytokine release, and apoptosis.**_*[83] The mechanisms by which these processes lead to the characteristic morphology of pseudomembranous colitis are incompletely understood.

Answer 67

Fully developed C. difficile–associated colitis is **accompanied by formation of pseudomembranes**( Fig. 17-29A , B), made up of an**adherent layer of inflammatory cells and debris at sites of colonic mucosal injury**. While **pseudomembranes are not specific** and **may occur in ischemia and necrotizing infections**, the **histopathology of C. difficile–associated colitis is striking.** The surface epithelium is denuded, and the superficial lamina propria contains a dense infiltrate of neutrophils and occasional fibrin thrombi within capillaries. **Superficially damaged crypts** are di***_stended by a mucopurulent exudate that forms an eruption reminiscent of a volcano_*** ( Fig. 17-29C ). These exudates coalesce to form the pseudomembranes.

Answer 68

FIGURE 17-29 Clostridium difficile colitis. * A, The colon is coated by tan pseudomembranes composed of neutrophils, dead epithelial cells, and inflammatory debris (endoscopic view). * B, Pseudomembranes are easily appreciated on gross examination. * C, Typical pattern of neutrophils emanating from a crypt is reminiscent of a volcanic eruption.

Answer 69

Risk factors for C. difficile–associated colitis include: * advanced age, * hospitalization, and * antibiotic treatment. The organism is particularly prevalent in hospitals; as many as 30% of hospitalized adults are colonized with C. difficile (a rate tenfold greater than the general population), but most colonized patients are free of disease.

Answer 70

Individuals with C. difficile–associated **colitis present with fever**, **leukocytosis, abdominal pain, cramps, hypoalbuminemia, watery diarrhea, and dehydration.** Fecal leukocytes and occult blood may be present, but grossly bloody diarrhea is rare.

Answer 71

Diagnosis of C. difficile–associated colitis is usually accomplished by **detection of C. difficile toxin**, rather than culture, and is supported by the characteristic histopathology. **Metronidazole or vancomycin** are generally effective therapies, but antibiotic-resistant and hypervirulent C. difficile strains as well as recurrent disease are increasingly common.

Answer 72

Whipple disease is a rare, multivisceral chronic disease first described as intestinal lipodystrophy in 1907 by George Hoyt Whipple. A mere 27 years later the pathologist went on to win the Nobel Prize for his work on pernicious anemia. He was a contemporary, but not a relative, of Allen Oldfather Whipple, the surgeon who pioneered the pancreatoduodenectomy.

Answer 73

Whipple's original case report described an individual with **malabsorption, lymphadenopathy, and arthritis of undefined origin.**

Answer 74

Postmortem examination demonstrated the **presence of foamy macrophages and large numbers of argyrophilic rods in the lymph nodes, providing evidence that the disease was infectious**. [85]

Answer 75

The **Gram-positive actinomycete**, named *_**Tropheryma whippelii,**_* that is responsible for Whipple disease was identified by PCR in 1992 and finally cultured in 2000. [86]

Answer 76

Clinical symptoms occur because **organism-laden macrophages accumulate within the small intestinal lamina propria** and **mesenteric lymph nodes,** causing **lymphatic obstruction.** Thus, the **malabsorptive diarrhea of Whipple disease is due to impaired lymphatic transport.**

Answer 77

The morphologic hallmark of Whipple disease is a *_**dense accumulation of distended,****foamy macrophages in the small intestinal lamina propria**_* ( Fig. 17-30A ). The macrophages contain **periodic acid–Schiff (PAS) positive**, diastase-resistant granules that represent lysosomes stuffed with partially digested bacteria ( Fig. 17-30B ).

Answer 78

Intact rodshaped bacilli can also be identified by electron microscopy ( Fig. 17-30C ). A similar infiltrate of foamy macrophages is present in intestinal tuberculosis ( Fig. 17-30D ), and in both diseases the organisms are PAS-positive. However, the acid-fast stain can be used to distinguish between these, since mycobacteria stain positively ( Fig. 17-30E ) **while T. whippelii do not.**

Answer 79

The villous expansion caused by the dense macrophage infiltrate **imparts a shaggy gross appearance to the mucosal surface**. Lymphatic dilatation and mucosal lipid deposition account for the common endoscopic detection of white to yellow mucosal plaques. In Whipple disease, **bacteria-laden macrophages can accumulate within mesenteric lymph** nodes, synovial membranes of affected joints, cardiac valves, the brain, and other sites.

Answer 80

FIGURE 17-30 Whipple disease and mycobacterial infection. * A, H&E staining shows effacement of normal lamina propria by a sheet of swollen macrophages. * B, PAS stain highlights macrophage lysosomes full of bacilli. Note the positive staining of mucous vacuoles in the overlying goblet cells. * C, An electron micrograph of one lamina propria macrophage shows these bacilli within the cell (top) and at higher magnification (inset). * D, The morphology of mycobacterial infection can be similar to Whipple disease, particularly in the immunocompromised host. Compare with A. E, Mycobacteria are positive with stains for acid-fast bacteria.

Answer 81

The clinical presentation of Whipple disease is usually a **triad of diarrhea, weight loss, and malabsorption**. Extraintestinal symptoms, which can exist for months or years before malabsorption, include arthritis, arthralgia, fever, lymphadenopathy, and neurologic, cardiac, or pulmonary disease.

Answer 82

* Norovirus * Rotavirus. * Adenovirus.

Answer 83

This was previously known as norwalk-like virus and is **a common cause of nonbacterial infectious gastroenteritis**. [87] These are **small icosahedral viruses** with a **single-stranded RNA** genome that forms a genus within the Caliciviridae family. Norovirus causes approximately half of all gastroenteritis outbreaks worldwide and is a **common cause of sporadic gastroenteritis in developed countries.** Local outbreaks are usually related to contaminated food or water, but **person-to-person transmission** underlies **most sporadic cases**. Infections spread easily within schools, hospitals, nursing homes, and, most recently, cruise ships.

Answer 84

Following a **short incubation period,**affected individuals develop**nausea, vomiting, watery diarrhea, and abdominal pain**. Biopsy morphology is nonspecific. When detected, abnormalities are most evident in the **small intestine and include mild villous shortening, epithelial vacuolization, loss of the microvillus brush border, crypt hypertrophy, and lamina propria infiltration by lymphocytes**( Fig. 17-31A ). The **disease is self-limited**.

Answer 85

FIGURE 17-31 Infectious enteritis. * A, Histologic features of viral enteritis include increased numbers of intraepithelial and lamina propria lymphocytes and crypt hypertrophy. * B, Diffuse eosinophilic infiltrates in parasitic infection. This case was caused by Ascaris (upper inset) , but a similar tissue reaction could be caused by Strongyloides (lower inset) . * C, Schistosomiasis can induce an inflammatory reaction to eggs trapped within the lamina propria. * D, Entamoeba histolytica in a colon biopsy specimen. Note some organisms ingesting red blood cells. * E, Giardia lamblia, which are present in the luminal space over nearly normal-appearing villi, are easily overlooked. * F, Cryptosporidia organisms are seen as small blue spheres that appear to lay on top of the brush border but are actually enveloped by a thin layer of host cell cytoplasm

Answer 86

This **encapsulated** virus with a **segmented double-stranded RNA** genome infects 140 million people and causes **1 million deaths each year**, making ***_rotavirus the most common cause of severe childhood diarrhea and diarrheal mortality worldwide_***. Children between **6 and 24 months of age are most vulnerable**.

Answer 87

Protection in the **first 6 months of life is** probably **due to the presence of antibodies to rotavirus in breast milk,** while **protection beyond 2 years is due to immunity that develops following the first infectio**n. [88] Outbreaks in hospitals and daycare centers are common, and infection spreads easily; the estimated minimal infective inoculum is only 10 viral particles.

Answer 88

Rotavirus **selectively infects and destroys mature enterocytes** in the small intestine, and the **villus surface is repopulated by immature secretory cells.** This results in loss of absorptive function and net secretion of water and electrolytes that is compounded by an osmotic diarrhea from incompletely absorbed nutrients. Like norovirus, rotavirus has a **short incubation period followed by several days of vomiting and watery diarrhea.** Vaccines are now available, and their use will probably change the epidemiology of rotavirus infection.

Answer 89

Adenovirus. The **second most common cause of pediatric diarrhea** (after rotavirus), adenovirus also **affects immunocompromised patients**. [89] Small intestinal biopsy specimens can show epithelial degeneration but more often exhibit nonspecific villous atrophy and compensatory crypt hyperplasia. Viral nuclear inclusions are uncommon. Disease typically presents **after an incubation period of 1 week with nonspecific symptoms that include diarrhea, vomiting, and abdominal pain.** Fever and weight loss may also be present. Symptoms generally resolve within 10 days.