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Like the other clostridia described in this section, C difficile has a most important medical feature: its ability to produce toxins. By adulthood, approximately 50% of individuals worldwide can be shown to have circulating antibodies against T gondii. Louis encephalitis has been much more prevalent in eastern states and in Texas, Mississippi, and Florida. Recently, many investigators have stopped using the term basement membrane and substituted the term basal lamina for both light and electron microscopic descriptions. It is unclear whether this transient resistance to disease is a result of host maturation factors or transplacentally conferred immunity. Speciation involves uncommon tests such as the decomposition of amino acids and casein. Porphyrin Disorders presence of ketones and homocystine, and additional tests may have to be performed. Failure to ferment lactose and the production of hydrogen sulfides from sulfur-containing amino acids are characteristic features used to identify suspect colonies on the selective isolation media. It is now recommended by expert obstetric and perinatology groups that all newborns at risk receive such prophylaxis. However, because ivermectin does not fully cure the individual patient, retreatment is required. The primary approach to prevention of all forms of genital and infant C trachomatis infection comprises detection of this infection in sexually active individuals and appropriate treatment, including infected women with erythromycin late in pregnancy. Although most cases of hepatitis A are not linked to a single contaminated source and occur sporadically, outbreaks have been described. Comparison of a typical retrovirus with a defective acute transforming retrovirus. Growth on all common isolation media is luxurious, and colonies have a delicate, fringed edge. The mosquito vector (A aegypti) is the same as the domestic vector of yellow fever. For unknown reasons, P multocida is occasionally isolated from the sputum of patients with bronchiectasis. Sustained growth is achieved only in animals (rabbit testes), which are the sole source of bacteria for diagnostic reagents and scientific study. Physical examination reveals tenderness over the costovertebral areas of the back and, occasionally, evidence of septic shock. Decreased volume is more frequently associated with infertility and may indicate improper functioning of one of the semenproducing organs, primarily the seminal vesicles. Patients are most contagious in the 1 to 2 weeks before onset of clinical disease. Taken together, these factors represent a rich armamentarium of virulence factors all linked to the change from yeast to hyphal growth. Although the polysaccharide capsule of C neoformans has antiphagocytic properties similar to those of encapsulated bacterial pathogens, it is less antigenic. The laboratory accuracy is evaluated and compared with other laboratories using the same method of analysis. The procedure can also be used to monitor patients undergoing treatment for malabsorption disorders. Instead, its first manifestation (in 25% of those infected) may be the presence of smoldering chronic hepatitis that may ultimately lead to liver failure. After transformation into filariform larvae, they are transmitted to another human host. In addition, it is possible to suppress clinical manifestations of infection, if they occur, with a weekly dose of chloroquine. A major focus of concern is susceptible women of childbearing age, who carry a risk of exposure during pregnancy.

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Their morphology, fastidious growth, and positive oxidase reaction can result in confusion with Neisseria in the laboratory. Helminths, with few exceptions, do not multiply within the human host, and severe infections usually require the repeated acquisition of infectious worms. Replication and assembly occurs exclusively in the cellular cytoplasm; one infectious cycle can occur within 6 to 7 hours. Condyloma acuminatum A wart-like infectious benign growth that occurs on the genitalia and in the anal canal. Ensure that reusable equipment is not used for the care of another patient until it has been cleaned and reprocessed appropriately. The extensive Golgi apparatus of this secretory cell presents several flattened membrane-bound cisternae (Ci), stacked one on top of the other. Less common chronic neurologic dysfunctions include subtle encephalitis affecting memory, mood, or sleep, and peripheral neuropathies. Species identification is based on a combination of biochemical, enzymatic, and morphologic characteristics, such as carbohydrate assimilation; fermentation; and the ability to produce hyphae, germ tubes, and chlamydoconidia. These small granules contain histamine and heparin, as well as additional substances. The X-ray shows consolidation of the right middle lobe of the lung, and a Gram stain of the sputum shows numerous neutrophils and lancet-shaped Gram-positive diplococci. In rare cases, fulminant fatal hepatitis associated with extensive liver necrosis may occur (0. The precipitation of inorganic chemicals dissolved in the urine forms urinary crystals and renal calculi. When all these factors operate in a sexually active population, it is easy to explain the high prevalence of gonorrhea. Moreover, glycoproteins also bind to collagen, thus facilitating cell adherence to the extracellular matrix. Because nonclostridial anaerobes and members of Enterobacteriaceae frequently contaminate injury sites, broad-spectrum cephalosporins are often added to the antibiotic regimen. They contain a prominent centrally located nucleus about the size of a red blood cell and a large amount of irregular cytoplasm, lacking granularity, with distinct cell margins. Quorum-sensing systems deploy expression of these virulence genes at a time when a critical mass of V cholerae is present to sustain it. Perinatal (mother-to-child) transmission-Strong recommendation (data from randomized controlled trials). Passive transport is the movement of molecules across a membrane as a result of differences in their concentration or electrical potential on opposite sides of the membrane. Correct specimen handling and timely transport to the laboratory is important for optimal detection of the responsible pathogen. The result is based on the measurement and computed processing of signal data from reflectance of fecal surface, which is scanned with infrared light between 1400 nM and 2600 nM wavelength. When there is more than one intermediate host, they are known simply as the first and second intermediate hosts. It may also be transmitted to newborns in the birth canal in a manner similar to group B streptococci. Although C jejuni is not the only antecedent to this syndrome, it is the most common of identifiable causes. Larval stages called cercaria emerge from snail and may either directly penetrate the final definitive host (the schistosomes), or encyst openly in the environment or within a second intermediate host (all other parasitic trematodes). Untreated, the mortality rate caused by the generalized disease varies from 15% to more than 60%, according to the lesion, incubation period, and age of the patient. Interleukin Class of cytokines produced by macrophages or T cells that mediate growth and differentiation of cells, particularly lymphocytes. Compounds such as cefepime have activity against a wider spectrum of Enterobacteriaceae as well as P aeruginosa. Myelin Component of the sheath around the axon of a neuron that increases the conduction velocity of the nerve impulse.

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In intravascular infections (eg, infective endocarditis), a single blood culture is positive in more than 95% of cases. The risk is greatest in equatorial Africa, where there is a high incidence of malaria. It is not uncommon for lactose intolerance to persist after eradication of the organisms. Movement occurs in helical waves and seems to be suited for organisms living within a viscous fluid environment such as that found in the blood stream. Fecal artifacts may appear as plant and meat fibers or as brown amorphous material in a variety of sizes and shapes. The interaction determines whether the purified genome of a virus is infectious V. In this manner, hemidesmosomes assist in the anchoring of epithelial sheets to the adjacent basal lamina. None is considered a proven cause of enteric disease, although no doubt some will be in the future. It interferes with cell division and possibly other cell functions associated with microtubules. The large number of nuclei present in the papillary layer of the dermis belong to lymphocytic infiltrate. They may account for an estimated 5% to 15% of all viral gastroenteritis in young children. When the mosquito vectors become abundant, the level of transmission among the basic reservoir hosts (birds and small mammals) increases, and the mosquitoes also turn to other susceptible species such as the domestic fowl. These methods are rapid and specific, but are at best only 90% sensitive compared with culture. The lac operon consists of three genes: lacZ, lacY, and lacA, which are transcribed as a single unit from the lac promoter. Folliculitis of the skin may follow soaking in inadequately decontaminated hot tubs that can become heavily contaminated with the organism. In different stages of the asexual cycle, it is referred to by several other terms, including merozoite and tachyzoite. However, in 1990 and 2008, few human asymptomatic cases with evidence of antibodies against the virus were reported. Preexposure prophylaxis consists of three doses of intramuscular injections (deltoid area) of vaccine on Days 0, 3, and 21 or 28. Vancomycin-resistant enterococci have enzyme systems that substitute a different amino acid in the terminal position of the peptidoglycan side chain (often alanyl lactate instead of alanyl alanine). A second syndrome involves many major organ systems, with particular damage to the liver, as in yellow fever. Initially, it was believed that little or no viral replication occurred during this latent period, but studies of lymph nodes of individuals with early asymptomatic disease have shown intense immunologic reactions within the lymphoid tissue at early stages of disease. The most common is chloroquine resistance, wherein the parasite reduces the amount of drug that accumulates in its digestive vacuoles. It grows overnight under anaerobic conditions, producing hemolytic colonies on blood agar. In addition to humans, a number of wild and domestic animals, including rats, cats, dogs, opossums, racoons, and armadillos, serve as reservoirs for Chagas disease. Granules at the periphery of the cell are released by fusion with the cell membrane, whereas granules deeper in the cytoplasm fuse with each other, forming convoluted intracellular canaliculi that connect to the extracellular space. Both drugs must be taken for prolonged periods of time, may cause serious side effects, and do not always result in parasitologic cure. Although elaborate systems are available for this purpose, the simple anaerobic jar is sufficient for isolation of the clinically significant anaerobes. The cell-by-cell extension of this process radially destroys enterocytes and creates focal ulcers in the mucosa, particularly in the colon. Investigation by Chaffee County public health officials indicated that the cat, reported to have submandibular abscesses and oral lesions consistent with feline plague, died on august 19 before being evaluated by a veterinarian. For generations, these worms were felt to be harmless to patients, and their importance in parasitology was limited to distinguishing them from "pathogenic" microfilariae found in the blood.

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Although they are capable of infecting humans, they cannot complete their life cycle in the human host. Primary components of the lens system are the oculars, the objectives, and the coarse- and fineadjustment knobs. These possible sources include middle ear infection (otitis media), mastoiditis, sinusitis, or pyogenic infections of the skin or bone. There are substantial differences in their genomic sequences particularly in the unique coding regions of each herpesvirus. The brain is not a particularly anaerobic environment, but brain abscess is most often caused by these same oropharyngeal anaerobes. Superimposed on this complex regulatory network is the fact that the viral promoter contains elements that are sensitive to specific cellular transcription factors. From the nasal site, the bacteria are shed to the exposed skin and clothing of the carrier and others with whom they are in direct contact. The digestive tract begins at the oral sucker and continues as a muscular pharynx and esophagus before bifurcating to form bilateral ceca that end blindly near the posterior extremity of the worm. They differ from the opportunistic fungi in their ability to cause disease in previously healthy persons, but the most serious disease still occurs in immunocompromised persons. Taxonomists vacillate as to whether they should be called species or something else. Humans become involved when they enter forested areas to harvest chicle for chewing gum and are bitten by infected sandflies. Because there are no differences in disease and clinical laboratories cannot distinguish the two, the more familiar C immitis is used for both species here. Additionally, the gaps and overlaps are arranged so that they are in register with those of neighboring (but not adjacent) rows of tropocollagen molecules. A chronic form of C trachomatis conjunctivitis, called trachoma, is the leading preventable cause of blindness in the world. Some virologists remain legitimately concerned that an animal poxvirus, such as monkeypox, could mutate to become highly virulent to humans-a further reminder that complacency could be dangerous. Although their virulence is very low, viridans strains can cause disease when they are protected from host defenses. All sharp objects must be disposed in puncture-resistant, leak-proof container with the biohazard symbol. Dental plaque cannot be effectively removed from the teeth solely by chemical or enzymatic means, and the use of antibiotics for prophylactic Porphyromonas gingivalis Tr ep on em as Salivary agglutinin Fusobacterium nucleatum Streptococcus gordonii Propionibacterium acnes Alpha-amylase pp. To distinguish between those two conditions, an absolute neutrophil count should be performed. There may be an acute transient glomerulonephritis in falciparum malaria and progressive renal disease in chronic P malariae malaria. The mechanisms involved have been more extensively studied in gonococci but appear to be similar in both species. These differences are presumably due to enhanced virulence factors in these types, but the specific reasons are not known. Resistance to multiple antimicrobials usually active against Gram-positive cocci, including vancomycin, is more common than with S aureus. The spores survive boiling for varying periods and are sufficiently resistant to heat that those of one species are used as a biologic indicator of autoclave efficiency. In the other form called specialized transduction, the genes that can be transduced are limited because of their placement adjacent to a special attachment site (att) in the bacterial chromosome. This stimulation probably accounts for the tendency of the organism to locate in these sites. Meningitis is the most common form and most often attacks those under 2 years of age. Moreover, the rough endoplasmic reticulum (r) presents dilated cisternae, indicative of protein synthetic activity. For example, persons known to have been exposed to highly infectious and virulent pathogens like N meningitidis (meningitis), Bacillus anthracis (anthrax), or Yersinia pestis (plague) can abort an infection during the incubation period by the administration of ciprofloxacin. The upper prism is placed between the objective and the eyepiece and recombines the rays.

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Therefore, the interpretation of routine and special procedures will be discussed individually for each of the three serous fluids. Another approach is to perform an enterotest, in which a bead encapsulated in a gelatinous capsule and attached to a thread is swallowed and then retrieved. Leishmania species, capable of neither of these feats, are resistant to the action of lysosomal enzymes and survive in macrophage phagolysosomes. The life span of the adult helminth is often measured in weeks or months, but some, such as the hookworms, filariae, and flukes, can survive within their hosts for decades, producing chronic infections with attendant morbidity or mortality. Infection typically involves the tonsillar pillars, uvula, and soft palate, which become red, swollen, and covered with a yellow-white exudate. The rapid tests are based on the detection of Clf, protein A, and other structures unique to S aureus. Obviously, chronic infection of the bloodstream is serious, and the effects of endotoxin can lead to myocarditis, encephalopathy, or intravascular coagulation. The pipettes are also used for sediment resuspension and transferring specimens to the slide. It must be remembered that cold hemagglutinins are nonspecific and have been observed in adenovirus infections, infectious mononucleosis, and some other illnesses. Despite this ubiquity, clinically apparent systemic fungal infections are uncommon, even among persons living within the geographic habitat of the more pathogenic species. Because of its specialized nature, the availability of antifungal susceptibility testing is restricted to major centers and reference laboratories. These unwitting adults are the major source for outbreaks in highly susceptible populations, such as infants. Crystal-induced origin Color and Clarity A report of the gross appearance is an essential part of the synovial fluid analysis. In Gram-negative bacteria acylated homoserine lactones and ketones (-hydroxyketone) have been shown to carry out these functions. Lymphocytes, neutrophils, and occasional eosinophils also contribute to the cellularity of loose connective tissue. As with other fungi, the application of modern genotyping methods has led to some splitting within Coccidioides. Plasmids are found in most species of Gram-positive and Gram-negative bacteria in most environments. Multiple counterparts of intermediate filaments are formed from a mixture of proteins, some of which are unique to bacteria. These cellular genes are called protooncogenes, and insertional activation by the virus is apparently due to the close proximity of the integrated viral promoter or enhancer to the gene. It is particularly common in areas of Central Asia, the Indian subcontinent, Middle East, Africa, the Mediterranean littoral, and Central and South America. Within this insect, they transform into filariform larvae capable of infecting another human when the vector again takes a blood meal. Failure to mix a specimen before inserting the reagent strip will primarily affect the: A. This dual life is facilitated by a surface protein able to bind a constituent of chitin as well as glycoproteins and lipids on the intestinal epithelium. The procedure varies depending on the hepatitis B status of the "donor" case linked to the injury. They are most frequently associated with the nephrotic syndrome, but are also seen in toxic tubular necrosis, diabetes mellitus, and crush injuries. The inflammatory condition initially confined to the gingival tissues can quickly extend into pathologic bone resorption. Occasionally, terms such as macroconidia and microconidia are used to indicate the size and complexity of these conidia. This coformulation (Malarone) is popular in malaria prophylaxis because it is effective and well tolerated-although, like mefloquine, it will not protect against malaria liver infection.

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Immune complexes shunted to the systemic circulation may induce glomerulonephritis. Group A streptococci are divided into more than 100 serotypes based on antigenic differences in the M protein. The goal is to simultaneously kill microfilariae with the antihelminthic while gradually killing-or at least rendering sterile-the adult worms with the antibiotic. Gonorrhea is a disease in which there appears to be no natural immunity and reinfections are common. The ulcers add a hemorrhagic component and allow Shigella to reach the lamina propria, where they evoke an intense acute inflammatory response. Even though convalescent human carriage is brief, if the numerous vibrios purged from the intestines of those infected with cholera are able to reach the primary water supply, the conditions for spread are established. In countries such as India, Pakistan, and Sri Lanka, where eradication efforts had previously interrupted parasite transmission, the disease incidence has increased 100-fold in recent years. They include numbness, paresthesia, loss of vibration sense, and, rarely, optic atrophy with central scotoma. If a second animal feeds on the infected flesh of the original host, the encysted larvae are freed by gastric digestion, penetrate the columnar epithelium of the intestine, and mature just above the lamina propria. A diagnosis in these cases, however, often depends on the detection of circulating antibodies via immunoblot technique. Staphylococcus aureus isolates can be subdivided by a variety of typing systems and by their pattern of lysis by bacteriophages (phage typing). Finding their route blocked, they rupture into the alveolar spaces, are coughed up, and subsequently swallowed. It is probable that the T lymphocytes act partially through their helper effect on antibody production. Some studies of urethritis and cervicitis have shown a higher rate of disease in those colonized but others have not. The other genus, Rubivirus that includes rubella virus is discussed in Chapter 10. Some Gram-negative bacilli fail to conform to any of the species currently recognized. The alkaline conditions provided by vegetables, such as green beans, and mushrooms and fish particularly support the growth of C botulinum. T -independent antigen Antigen that directly stimulates B cells without involvement of T cells. Amorphous Ground Substance the amorphous ground substance constitutes the gellike matrix in which the fibers and cells are embedded and through which extracellular fluid diffuses. The organisms in this group are substantially more resistant to antituberculous drugs than most other species, and treatment with the three or four agents found to be most active often requires supplementation with surgery. Metacyclic trypomastigotes inoculated by a tsetse fly usually contain a population of organisms dominated by a distinctive antigenic type. Lassa fever also frequently causes hepatitis, myocarditis, exudative pharyngitis, and acute deafness. All three agents are active against streptococci, retain some antistaphylococcal activity, and are highly active against both -lactamase-positive and -negative strains of gonococci and H influenzae. In the Eastern Hemisphere, the desert gerbil and other burrowing rodents serve as the reservoir hosts of L tropica. Vaccinia-produced immunity to smallpox wanes rapidly after 3 years, and the duration of long-term immunity beyond that time is uncertain. They appear to satisfy their protein requirements by the degradation of hemoglobin within their acidic food vacuoles, resulting in the formation of the malarial pigment (hemozoin) mentioned previously. Many of the more than 80 other nontoxigenic clostridial species are also associated with disease. The risk of clinically evident disease is much higher in infected adults than in children. Suitable mixtures of donor and recipient cells can lead to nearly complete conversion of all the recipients into donor, plasmidcontaining cells. Both the gray matter and the white matter of the brain are involved, the most noteworthy feature being the presence of intranuclear and intracytoplasmic inclusions in oligodendroglial and neuronal cells. More than 30 other viral agents, which are discussed later in this chapter, can produce a similar illness.

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Adequate disinfection can be accomplished with halogen tablets yielding concentrations higher than that generally achieved in municipal water systems. Indirect hemagglutination and latex agglutination tests are positive in 90% of patients with hepatic lesions and 60% of those with pulmonary hydatid cysts. This electron micrograph of fibroblasts (F) demonstrates that they are long, fusiform cells whose processes (p) extend into the surrounding area, between bundles of collagen fibrils. This fact appears to be due to the combination of easy penetration of Gram-negative and Gram-positive bacterial cells and high level of resistance to -lactamases. Two dilutions are made on the specific fluid based on the type of fluid and the appearance of the fluid. Intravenous ribavirin has been suggested for patients with severe measles pneumonia, but no controlled studies have been performed. As a result, increased urobilinogen is produced, and increased amounts of urobilinogen are reabsorbed into the blood and circulated through the kidneys where filtration takes place. The number of human infections produced by the other species together is far lower than that produced by P aeruginosa alone. The organism can usually be isolated on agar plates seeded with a Gram-negative bacillus (to feed the amebas) or grown axenically in tissue culture. Large bacterial populations may secrete enough -lactamase to inactivate the antimicrobial before it even reaches the organisms. Dental caries is the single greatest cause of tooth loss in the child and young adult. When using this chart, the higher of the protein-low or protein-high result is used2. The E genes are required for viral genomic replication, which in turn is required for optimal synthesis of most L genes. These result from alterations in the frequency of productive motion called a run and tumbling in place. Enhanced production of these receptors under various conditions, such as elevated glucose concentration, is associated with resistance to phagocytosis by neutrophils. Indicanuria Under normal conditions, most of the tryptophan that enters the intestine is either reabsorbed for use by the body in producing protein or is converted to indole by intestinal bacteria and excreted in the feces. This must be done without touching the person or the equipment involved to avoid transferring the current. Of particular importance is their expanded activity against Enterobacteriaceae species, although in theory this comes at the cost of reduced effectiveness against certain Gram positives. Louis Pasteur made a convincing field demonstration at Pouilly-le-Fort to show that vaccination of sheep, goats, and cows with an attenuated strain of B anthracis prevented anthrax. Quorum sensing Process by which bacteria use signal molecules to monitor their population density. Color is measured by either reflectance photometry or spectrophotometry at multiple wavelengths. Although stool surveys in the United States indicate that 1% to 5% of the population harbors Entamoeba, the majority of these are now known to be colonized with the nonpathogenic E dispar. Under these conditions, the poor are the major victims, but all sectors of society are at risk. Inferences from animal studies and clinical observations suggest that both humoral and cell-mediated immunity are important. In otitis media cases, M catarrhalis has been detected in mixed culture with pathogens like Haemophilus influenzae and Streptococcus pneumoniae. In acute symptomatic clonorchiasis, there is usually leukocytosis, eosinophilia, elevation of alkaline phosphatase levels, and abnormal computed tomography and ultrasonographic liver scans. Exponential (or logarithmic) growth period the period of time in the culture growth cycle in which the growth rate is maximal and constant. Schizogony Asexual reproduction in sporozoa producing merozoites by multiple nuclear fusion followed by cytoplasmic segregation.

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The patient may also be screened for elevated levels of IgM in the blood and spinal fluid or specific trypanosomal antibodies by a variety of techniques. The standard toxin assays involving cytopathic effect in cell culture have now been replaced by immunoassays, which demonstrate toxin TcdA and/or TcdB in stool. The inherited defect in Hartnup disease affects not only the intestinal reabsorption of tryptophan but also the renal tubular reabsorption of other amino acids, resulting in a generalized aminoaciduria (Fanconi syndrome). It is particularly difficult to distinguish from other inflammatory conditions or malignancies. The assignment of species names has little clinical importance beyond differentiation from P aeruginosa. In addition, there is evidence that certain enteroviruses, particularly group B coxsackievirus serotypes, may sometimes participate in the pathogenesis of insulin-dependent diabetes mellitus, acute arthritis, polymyositis, and idiopathic acute nephritis. Its modification as penicillin V confers acid stability, so it can be given orally. It is felt that this accounts for the ability of C burnetii to produce infection by aerosol inhalation, often at considerable distance from the presumed source. Rickettsia rickettsii does not kill its arthropod host, so the parasite is passed through unending generations of ticks by transovarial spread. Persons with chronic hepatitis B who acquire superimposed infection with hepatitis D suffer relapses of jaundice and have a high likelihood of developing chronic cirrhosis. Although the transfer of resistance genes by transduction has been demonstrated in the laboratory, its association with clinically significant resistance has been uncommon. This localization results in endothelial proliferation and a perivascular infiltration of plasma cells and lymphocytes. By the age of 5 years, almost all individuals have humoral antibodies, suggesting a high rate of virus infection early in life. This in turn leads to aneurysms of the ascending and transverse segments of the aorta and/or aortic valve incompetence. One of the longest known of these are the "on" and "off " states of flagellar genes explaining their phase variation. Immunity to reinfection does not appear until early latency, and for at least one-third of those infected the subsequent host response is successful in clearing most but not all of the treponemes. The occurrence and distribution of tick-borne relapsing fever are determined by the biology of multiple species of a single tick genus (Ornithodoros) and their relation to the primary Borrelia reservoir in rodents and other small animals (rabbits, birds, lizards). The resistance conveyed by these actions is usually high level; the chemically modified aminoglycoside no longer binds to the ribosome. Of all the Enterobacteriaceae, Klebsiella species are now among the most resistant to antimicrobial agents. With this procedure, 85% to 95% of infections are detected, in contrast to only 50% to 75% by stool examination. It can be made selective for fungi by the addition of antibacterial antibiotics such as chloramphenicol and gentamicin. Parapoxvirus genus members cause disease mainly in animals but sometimes also in humans, including orf and pseudocowpox viruses. Infections with this agent are seen only in South America at intermediate altitudes, in keeping with the distribution of its sandfly vector. The dominant strain of the 20th century was the El Tor biotype, first isolated from Mecca pilgrims at the El Tor quarantine camp in 1905. Some plasmids can be transferred only to closely related strains; others can be transferred to a broad range of species within and beyond their own genus. Continuing surveillance also includes studies of poxviruses of animals (eg, buffalopox, monkeypox), which are antigenically somewhat similar to smallpox. The liver is enlarged and tender, and serum aminotransferase and bilirubin levels are elevated as a result of hepatic inflammation and damage. Fifty percent of recent infections have involved American travelers: Nearly 60% of these acquired their infection in Africa. Humans are infected with larval forms through the ingestion of eggs passed in the feces of their domestic dogs or ingestion of egg-contaminated vegetation.