However, Salmonella can also disseminate into deeper tissue beyond the intestine by virtue of intestinal dendritic cells. These etiologies can be differentiated by the clinical presentation of the patient and by the results of laboratory tests of the joint fluid. The organisms are present in large amounts in the placenta and fetal membranes and are spread in copious numbers when ewes give birth. In general, these are 248 Part 2: Infectious Agents also water-related infections, and they produce clinical features comparable to Legionnaires disease, for example, Legionella micdadei. Various pneumococcal strains express capsules with distinct sugar constituents or the same array of sugars linked in various ways. A serological test for Rocky Mountain spotted fever and cultures of the blood, cerebrospinal fluid, and urine were negative. This response typically limits the infection, and very few bacteria are found in infected lymph nodes. There are various ways in which disease-causing agents can be acquired from the environment: food, water, air, objects, insect bites, or humans or animals with whom we share our environment. Thus, a number of conditions predispose to skin invasion, including excessive moisture, trauma, introduction of a foreign body, pressure, and compromised blood supply. Spinal paralytic poliomyelitis, which involves weakness and asymmetric flaccid lower limb paralysis, comprises less than 1% of all infections and is accompanied by an approximately 10% fatality rate. Chronic bacterial prostatitis is usually characterized by recurrent episodes of acute cystitis from relapses of bacteria persisting in the prostate. She showed no signs of endocarditis, and a lumbar puncture was negative for bacterial meningitis. Where there are no cats (such as on certain Pacific islands), there is no toxoplasmosis. In the endemic areas of South and Central America, most persons are infected by T. Amidase is another enzyme in the skin and serum that hydrolyses bacterial cellwall peptidoglycan, although in contrast to lysozyme, it does not have a direct bacteriolytic activity. The exception is onychomycosis, which always requires systemic antifungal agents to achieve an effective response. Although a single B cell can manufacture a single type of warhead, it can be placed on different rockets. These tests rely on agglutination of the organisms by antibodies present in patient sera. These macrophages are replenished by the arrival and differentiation of monocytes from the bone marrow. However, when the airborne inoculum is large, or when host defenses are compromised, exogenous reinfection can occur. It is estimated that approximately 500,000 cases of pneumococcal pneumonia occur each year in the United States. Persons who have lived in malarious areas all their lives and who have evidence of humoral and cellular responses to parasite antigens are nevertheless infected on a regular basis. The only rickettsial disease that can be expected to have diagnostic levels of antibodies at the time the patient seeks medical attention is chronic Q fever. Most antisera are polyclonal mixtures of antibodies that bind to different domains of different antigenic molecules. The smallest viral genomes encode three or four proteins, and the largest encode more than 100 structural proteins and enzymes. Other organisms, like the pneumococcus, are not killed by complement alone but require phagocytosis by neutrophils or macrophages, the professional phagocytes. The surgeon decided that reexploration of her abdomen was warranted because of persistent sepsis in the presence of broad-spectrum antimicrobial therapy. This is also the major obstacle to developing a truly effective vaccine against this pathogen. Encounter and Entry: Pathogens are usually transmitted to humans in contaminated food and water. Certain bacteria, including the Gram-negative typhoid bacillus and Gram-positive enterococci, are so highly resistant to bile that they can even grow in the gallbladder. Although these effects are weak, they led to the synthesis of an important group of modern diuretics.
Measures to promote oxygen delivery should be included, supplying the patient with air that has a high oxygen content, using a ventilator or other mechanical device to keep the airways under pressure throughout the respiratory cycle, and transfusing to maintain adequate hemoglobin concentrations. Fungal and viral pathogens can also be tested for drug susceptibility, but those tests are beyond the capabilities of most clinical microbiology laboratories. It is also recommended that treatment be initiated in those groups at the onset of endemic influenza in the community. Cells of the innate immune system are the gatekeepers of the adaptive immune response. At that stage the organism can be isolated not only from blood but also from stool and urine. Once growth is detected, microorganisms from cultures are transferred to agar plates, or subcultured, to permit species identification. Leukocyte Chemotaxins: Sounding the Alarm We have already seen that a product of complement activation, C5a, is an attractant for neutrophils and monocytes. The upper intestinal contents, rich in unabsorbed sugars, fats, and other nutrients, do not normally come in contact with large numbers of bacteria. Because of the exceptionally high fevers in spite of heroic efforts to reduce body temperature, all patients thus far described have succumbed. F protein mediates fusion of the viral envelope and the host cell membrane and release of the viral genome into the cytoplasm to begin the virus replication cycle. Although these modes of transmission may seem passive, many infectious agents contribute actively to their transmission to new hosts. This compound contains a nitro group that must be partially reduced to render the molecule active. Innate immunity refers to immune mechanisms that are always present and available for action. It is not known if other enzymes involved in cleaving host glycans contribute to the virulence of the Bacteroides when they are released to the peritoneal cavity, but this feature may allow these bacteria to use host-derived glycans as a source of nutrients in extraintestinal sites. Unlike other neisseriae, gonococci utilize glucose but not maltose or sucrose, and meningococci utilize both glucose and maltose. Recent progress has been made in vaccine development against meningococcal infection, but challenges remain for prevention of infection by N. It is thought that this slime layer allows the organisms to stick to the surface of plastics used in various devices. Patients can be identified by their failure to gain weight and high concentrations of sweat electrolytes. Six groups of rotaviruses (A through F) have been identified based on antigenic characteristics. In addition, since 1984, plasma products have been treated with heat and chemicals to inactivate contaminating viruses. Staphylococci are more likely to be isolated from brain abscesses in the setting of septic emboli from infected heart valves, trauma, or surgical procedures. The smear is then counterstained with a blue dye to provide a contrasting background. In contrast, the morphology of most bacteria is too simple to permit microscopic identification; however, a few exceptions exist. Developing molecular amplification methods for rapid diagnosis of respiratory tract infections caused by bacterial pathogens. Laboratory examination revealed a high white blood cell count and an elevated serum creatinine value (5. Activation of Complement Endotoxin activates complement by the alternative pathway (see Chapter 6). The recommended postexposure prophylaxis regimen varies based on history of previous rabies vaccination and immune status. Treatment of pneumonic plague must be started within 24 hours of onset of symptoms, or mortality approaches 100%. However, her systemic vascular resistance was extremely low, which accounted for her low blood pressure despite the high cardiac output.
Nonetheless, the role of genetic factors has been well established in certain diseases. The physician drained the lesion, and a culture of the pus grew a group A -hemolytic streptococcus (S. One type of microbial defensive strategy is making, or appropriating from the host, a protective covering. The net result is that, although some infected persons do clear acute infection, many do not and instead develop a persistent infection that frequently is lifelong. Supporting that hypothesis is the finding that nasal secretions of persons with colds contain large amounts of the vasoactive substance, bradykinin, and proinflammatory cytokines that recruit inflammatory cells into the infected area. This is largely attributable to repeated antimicrobial exposure with prior recurrent infection. The only other pertinent medical history was that the patient had recently begun treatment with corticosteroids for asthmatic bronchitis. Virus Protein Processing Following genome replication, production of viral proteins is an essential part of the replication cycle of all viruses. A microchip can be printed to contain hundreds of oligonucleotide probes bound in an array no bigger than a microscopic slide. Invasion strategies of Shigella compared with Salmonella in the intestinal epithelium. To drive the transport of lactose, the cells use energy stored in an electrochemical gradient of protons, the proton motive force. The surgeon excised part of the stomach and duodenum and connected the remainder of the stomach with the jejunum (gastrojejunostomy), bypassing the unresected duodenum. One limitation of polysaccharide capsular antigen is that they cannot activate T helper cells (Thcell). This chapter discusses how the innate immune system functions and how it protects us from infections. The American Academy of Pediatrics currently recommends universal vaccination with Tdap for adolescents at 11 to 12 years of age and a catch-up vaccination for older adolescents to boost protection against pertussis. This process can produce an intensely itchy, red, serpentine track around the site of penetration that can persist for weeks. Use of respirators when tearing down old barns and chicken coops or other areas that have housed birds and bats is highly recommended. That type of study is referred to as a cohort study since the individuals included in the cohort have specific characteristics in common but have not yet developed the disease of interest. This example of efficacy is based on the relative insensitivity of the host compared with bacterial targets. The toxin-mediated diseases (labeled in italics) are caused by streptococcal exotoxins that are secreted into the bloodstream. Furthermore, the small amount of oxygen that diffuses into deeper tissue layers can readily be used by host cells or by actively metabolizing aerobes and facultative anaerobes. Scanning electron micrograph of human fallopian tube tissue 20 hours after infection with Neisseria gonorrhoeae. Although you need to know only the principal bacteria, even they make up a long list. When inoculated intracerebrally with the virus, normal mice die within about a week. Chlamydophila pneumoniae infects the respiratory epithelium where it can cause acute bronchitis and pneumonia, but chronic respiratory infection is linked to enhanced asthmatic disease. T cells play a central role as arbiters of immune function; therefore, the manner in which T cells recognize and are activated by epitopes is highly regulated. Thus, for the past 30 years, penicillin has ceased to be the universal agent for the treatment of gonorrhea. Multiplication: A specialized bacterial secretion system establishes a protected intracellular replication vacuole. It is also partly responsible for a postenteritic syndrome seen in children, in whom mild diarrhea persists for a considerable time after the infection is resolved.
They are the price we pay for high responsiveness to microorganisms to fight the infection. An endocervical swab was collected for nucleic amplification assays for both chlamydiae and gonococci. Experimental studies suggest that suppression of toxin production by antibiotics that inhibit 658 Part 3: Pathophysiology of Infectious Diseases Fifty-two-year-old Mr. In addition to what they can teach us about infectious disease mechanisms, these factors are often targets for vaccine or drug discovery research. Unfortunately, antibodies to M protein can crossreact with similar structures found on the sarcolemma of cardiac muscle and on the heart valves. All the subsequent asexual stages in the human, up to and including the gametes, are haploid. This requirement for multiple cycles of replication and dissemination accounts for the 10- to 14-day incubation period for measles. With extensive exposure, even in healthy hosts, bilateral diffuse nodular infiltrates, hypoxemia, and acute respiratory distress syndrome can occur. Acute epiglottitis occurs most often in children 2 to 7 years of age, with the most common cause being Haemophilus influenzae type b. This ability to invade and cause inflammation is necessary but not sufficient to cause diarrhea in experimental animals. When the component is cleaved in the process of activation, its fragments receive an additional letter, a or b. Antibodies specific for measles virus mediate protection against disease and may play a role in clearance of acute infection. Particular examples are strains of enterococci resistant to most available antibiotics. Vegetations vary in size from a few millimeters to a centimeter or larger and may be single or multiple. Antiviral therapy for herpesvirus central nervous system infections: neonatal herpes simplex virus infection, herpes simplex encephalitis, and congenital cytomegalovirus infection. During treatment, central nervous system symptoms may transiently worsen because of the inflammatory response to dying cysticerci. Proptosis is caused by the edema and inflammatory exudate in the orbit, literally making the cavity smaller and forcing the eye outward. Many factors affect the distribution, composition, and density of these microorganisms. Although the reason for this distribution is not known, poverty and a debilitated state of health are risk factors. In Lyme disease, the most common form of chronic central nervous system involvement affects memory, mood, or sleep, sometimes with subtle language disturbance. Some of the conserved proteins appear to form a pore within the host cell membrane, through which other proteins can pass into the cytosol of the host. The ticks molt into adults in the fall, and while their preferred host is deer, they can occasionally feed on humans, giving rise to a smaller peak of human Lyme disease in the fall. Each antibody in the population recognizes a single epitope and therefore, most likely, a single factor expressed by the bacteria during the course of infection. The obligate intracellular parasites are very small relative to the other pathogens discussed in this chapter. Before the advent of effective antiretroviral therapy, it was necessary to carefully weigh whether low-risk individuals should be tested. Several related viruses (other enteroviruses) continue to cause important diseases in the United States. Vaccines that protect solely or principally by induction of serum antibodies include hepatitis A, polio, rabies, yellow fever, diphtheria, pertussis, tetanus, and extracellular encapsulated bacteria. Generalized tetanus, responsible for about 80% of cases, usually begins with trismus, or "lockjaw. This pattern suggests that late-onset staphylococcal prosthetic endocarditis is probably acquired as a consequence of transient bacteremia. Dengue viruses multiply in the gut of a mosquito, spread to its salivary glands, and are injected into a human as the mosquito takes a blood meal.
It is likely that additional factors that have yet to be identified and characterized also contribute to the ability of B. However, small numbers of bacteria in urine grow well at room temperature, so specimens must be promptly forwarded to the laboratory following collection. Spirochetes these bacteria are helical, having the shape of a spring (not a screw). As short-course therapy of 3-day A 23-year-old woman presents with a 48-hour history of dysuria, frequency, and gross hematuria. However, this only begs the question, "How do you recognize an epitope that you have never seen But the peril with this approach is that without some means of identification, molecules of self origin that were not seen during lymphocyte development could possibly trigger a response. Special varieties of this medium are known as Thayer-Martin medium and Martin-Lewis medium; each contains unique antibiotics to inhibit other bacterial species and yeasts found in the genital tract. Nevertheless, pneumococcal pneumonia remains the most common form of communityacquired bacterial pneumonia and continues to be fatal in up to 5% of all patients, with higher mortality rates in elderly or debilitated patients and those with bacteremia, even when they are treated with an antibiotic to which their organism is sensitive. Potentially effective public health measures and their rationales are shown in Table 55-2. If used within 2 days of symptom onset, symptoms of infections resolve more rapidly, and virus shedding is diminished. The major causative agent of bacillary angiomatosis, Bartonella henselae, was initially identified using this approach. More than 10,000 nonencapsulated pneumococci must be injected into the peritoneal cavity to kill a mouse, but only about 10 encapsulated bacteria are required-a 1,000-fold difference in virulence. Reactivation results in spread of virus along sensory nerves to mucosal surfaces, producing recurrent herpes labialis (cold sores) or herpes genitalis. Auscultation may reveal crackles (also called rales) and peripherally auscultated bronchial breath sounds, which are usually indicative of alveolar disease. The objective of immunization program has been responsible for spectacular advances in combating the infectious diseases such as smallpox, poliomyelitis, tetanus, diphtheria, etc. However, these attenuated strains can still induce protective humoral and cellular immune responses. They will not reproduce if incubated aerobically, and their growth requires special anaerobic techniques. Human and animal herpesviruses are divided into three subfamilies (alpha-, beta-, and gammaherpesviruses) based on their evolutionary relationships and biological properties. An earlier view was that decreased resistance of peripheral vessels results from a buildup of vasoactive amines (histamine and kinins). The reason for that predilection is uncertain but may stem from degenerative bony changes and vascular proliferation in the disk space between the vertebrae, which normally occur with age. That paradox illustrates the biological principle that successful parasites generally do not harm the host. Thus, it is important to understand the pathogenesis of this persistent bacterial infection and how H. A large number of cell-associated and secreted molecules participate in the pathogenesis of P. The ease of international travel and the threat of bioterrorism have caused concerns that relatively exotic pathogens (Ebola virus, Lassa fever virus, and West Nile virus) or viruses from the past (smallpox virus) may appear unexpectedly. Blood cultures were drawn, antibiotics were started, and intravenous fluids were rapidly infused to stabilize her blood pressure. She was slightly anemic (hematocrit of 29%) and had an increased number of reticulocytes. However, mosquitoes that can serve as vectors (Anopheles) exist in the United States. Some neurotropic viruses reach the brain through peripheral nerves or olfactory nerve endings. In turn, these molecules may damage tissues, making iron more accessible to the organism. Cutaneous Responses to Bacterial Toxins (Toxic Shock Syndromes and Scarlet Fever) the skin can respond to toxins elaborated during infections that take place at a distant site.
The organism that causes gas gangrene, Clostridium perfringens, produces multiple virulence factors and is highly tissue invasive. Both stages (adult and larval) and both hosts (cattle and humans) are required to complete the life cycle of the tapeworm. Encounter with the appropriate antigen containing multiple recognized epitopes causes IgE cross-linking, triggering the release of cytoplasmic granules from the cell. The reflux of infected blood during menstrual uterine contractions may also provide a route of entry into the fallopian tubes. As with plague, transmission of the infection among those animals occurs through the bites of ticks, flies, and mosquitoes. Resistance poses a serious problem when it arises in a pathogenic microbe capable of causing damage to human hosts. Their role in human disease has been clearly established because the administration of specific antitoxin prevents the skin lesions in humans or mice. By contrast, it is possible for antibodies cross-reactive to microbial antigens to play an insidiously harmful role in health. Some, like an agent of pneumonia, Mycoplasma pneumoniae, contain sterols in their membranes, an unusual feature among prokaryotes. Advanced tetanus may lead to opisthotonos, the bending backward of the body caused by spastic paralysis of the strong extensors of the back. Chemotactic factors, derived both from bacteria and complement, are made in large amounts. Tissue injury mediated by deposition of circulating immune complexes occurs in the skin, choroid plexus, spleen, and synovium. A chest radiograph showed an infiltrate in her left lower lobe consistent with pneumonia. This point is illustrated in people who have genetic or acquired defects in their immune systems. If appropriate treatment is initiated early in the course of infection, before significant bone necrosis occurs, patients usually respond quickly, and cure can be achieved in more than 90% of cases. Deficiencies in cationic proteins have been described in patients with chronic skin infections and abscesses. Physical examination revealed an ill-appearing, somnolent infant with mild dehydration and hyperactive bowel sounds. This number actually underrepresents the problem, as the majority of infected fetuses likely die in utero. For adenovirus, coxsackie A21 virus, and influenza A virus, as few as 10 particles may suffice. Intracellular Life Many bacteria, protozoa, and fungi have adapted to intracellular existence within the host. Utilization of multiple receptors may be important to ensure precise targeting of the virus to particular host cells. Although appropriate animal models have been developed to study the pathogenesis of acute P. Diaphragms are usually used with spermicide, however, and this remains the major determinant of infection in these women. In most instances, the infectious agent must develop and multiply within the vector before it can be transmitted. The tragic death of a human volunteer in an adenovirus gene therapy trial in 1999 points out the social and ethical problems that also accompany the development of gene therapy. Several studies have demonstrated that ureaplasmas can cause congenital pneumonia and are associated with chronic lung disease in premature infants with very low birth weights. Many components of innate and adaptive immunity act to defend against viral infections. Ketoconazole, the first oral azole, had a significant number of side effects and drug interactions and has largely been supplanted by itraconazole, with greater intrinsic activity against many fungi and an improved safety profile. The transcripts differ in abundance, which allows the synthesis of each viral protein to be regulated independently. In the lungs of mice infected with the high virulence virus, diffuse airspace obliteration is seen, with a majority of alveoli filled by inflammatory cells and debris.
While macrolide antibiotics have been considered first-line treatments, within the past decade, there have been reports from Asian countries as well as Europe and the United States of M. Vaccines against yellow fever, Japanese encephalitis, and tickborne encephalitis are available and should be used by travelers going to regions where exposure to these viruses is likely. All are important human pathogens deserving of continued studies into mechanisms of pathogenesis and immunity. She also recalled that her mother had a positive tuberculin skin test about 20 years ago, but her mother was never ill. Diagnosis: Depends on clinical suspicion and acumen, since laboratory studies are seldom helpful in establishing a diagnosis during the acute stage Treatment and Prevention: Rickettsial infections can be treated with antibiotics that penetrate into host cells. However, since 2005, a quadrivalent (serogroups A, C, Y, and W135) meningococcal vaccine has been included as part of the routine immunization schedule for 11- to 12-year-old children. Fermentation is characteristic of anaerobic bacteria, and indeed some streptococci are strict anaerobes. It hydrolyses peptidoglycan, the main structural component of bacterial cell walls. Four days later, his condition deteriorated, and he developed fever, chills, and shortness of breath (dyspnea), followed by nausea and vomiting. Chlamydia trachomatis is the most common cause of sexually transmitted disease (chlamydial urethritis) and other more unusual infections. Damage: Pertussis (aka whooping cough) is a disease that causes characteristic paroxysmal cough in infants and prolonged hacking cough in adults. Apathy and depression are common; less often, euphoria, emotional lability, and anxiety can occur. When some wild animals are bitten by Dermacentor ticks, they become transiently infected and a transient reservoir of the rickettsiae. Because mammalian cells do not have cell walls, the echinocandins are more selective than the agents discussed earlier that target the synthesis of cell membrane components. The organism can be documented by positive blood cultures in about 25% of all cases of pneumococcal pneumonia. In some hospitals, Pseudomonas isolates resistant to all available antibiotics have been encountered, portending a potentially frightening future unless novel means of controlling these bacteria are discovered. The membranes with their bound proteins were then incubated with the absorbed serum. The staining procedure is central in microbiology and, in due course, should be learned by every medical student. In active immunization, as the name implies, Routine Immunization While introducing immunization schedule, certain factors are taken into consideration. After they are taken up into phagosomes, the parasites differentiate into a nonflagellate form, called the amastigote. Less common than respiratory and gastrointestinal disease is adenovirus-induced conjunctivitis without other symptoms. Since then, hundreds of retroviruses have been isolated from many groups of vertebrates. Experimental infections have been induced in human volunteers who agree to drink buffered solutions containing a known number of living bacteria. This happens in tetanus, gas gangrene, and other diseases caused by sporulating bacteria. All individuals given such vaccination have developed the expected level of antibodies. As a result, the intensity of infection, called the worm burden, is determined by the size of single or repeated inocula. Structures in the bacterial cell wall or extracellular polysaccharides have been implicated in interactions with host tissue receptors that result in the adherence of selected organisms. Almost half the people infected with fish tapeworm have low levels of vitamin B12, leading to serious megaloblastic anemia. Not all of them stick, and many are soon carried through lymphatic channels to the systemic circulation. In addition, many more tick bites were reported by the arthritis patients than by their neighbors without the disease. Amebiasis may cause intestinal perforation or obstruction, or the organisms may spread to produce abscesses in other organs, especially in the liver.
After capturing an iron molecule, these compounds deliver the iron to specific bacterial receptors (see Chapter 3). Lipid A is an unusual glycolipid composed of disaccharides to which are attached shortchain fatty acids and phosphate groups. Because of their capacity for transient growth, such vaccines provide prolonged immune system exposure to the epitopes of the attenuated vaccine, so that there is increased immunogenicity and production of memory cells. Because of its broad spectrum, imipenem can wipe out much of the normal bacterial microbiota and lead to colonization by resistant species. Therefore, most new infections are acquired by ingestion of contaminated food or water. Thus, exclusion of hydrophobic compounds in Gram-negative bacteria, as in Gram-positive bacteria, relies on surrounding the cells with hydrophilic polysaccharides, although these polysaccharides differ in structure and organization in the two groups. Currently, inactivated vaccines and live, attenuated, cold-adapted vaccines are available. Likewise, for varicella vaccine, approximately 20% of persons 13 years of age or older will not respond to the first dose of vaccine, although almost 99% of persons will seroconvert after two doses. Hikers and campers can prevent unpleasant episodes of diarrhea by boiling or filtering their drinking water or by treating it with adequate amounts of iodine or chlorine. Eggs released into fresh water hatch to miracidia (8), which invade the snail intermediate host where they mature to sporocysts (9). Still, bacteria grow sparsely on fresh plasma in a test tube, primarily because of the presence of antimicrobial substances, such as lysozyme, constituents of the complement system, and antibodies. What makes chemotaxis so effective is that neutrophils are extraordinarily motile. The complexities of tissue tropism can be illustrated using the gonococcus as an example. Instead of being delivered to lysosomes, the phagosome associates with intracellular organelles. Another example is an infection of the middle ear, a condition more common in children than in adults. In this manner, cell-to-cell spread occurs without the need to reenter the extracellular milieu. Structural studies have elucidated mechanisms of drug resistance for the nonnucleoside inhibitors. For example, we now know that the annual incidence of Lyme disease in Connecticut (from 1992 to 1998) was 68 per 100,000 population, whereas in neighboring Massachusetts, the annual incidence was only 5 per 100,000 population, an almost 12-fold lower risk. The major components of the classical pathway are designated by the letter C followed by a number, for example, C3 (see Table 6-5). Evidence points to the formalin inactivation steps used in vaccine preparation possibly altering the conformation of the F protein, thus inducing lowaffinity antibodies that did not inhibit virus or protect recipients against infection. In this way, enterococci may acquire absolute resistance to penicillins or aminoglycosides that negates the benefits of antibiotic synergy. A serious potential for cross-contamination (microcontamination) exists in laboratories that process many similar samples every day. It is thought that measles virus became endemic within human populations when concentrated masses of people began living in urban areas. Adult worms of various roundworm species range in size from a few millimeters to 20 cm. These patients develop subcutaneous abscesses, lung abscesses, hepatic abscesses, lymphadenitis, pneumonias, and osteomyelitis. Rash and Arthritis Sindbis (also known as Ockelbo, Pogosta, or Karelian fever) and Ross River viruses are togaviruses that cause summertime outbreaks of rash and arthritis in northern Europe and Australia, respectively. About one-quarter of the patients had reported that the symptoms of arthritis were preceded by an unusual skin rash. These patients are at greater risk for infection with acid-sensitive bacteria like V.
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