Disease Flashcards
What is dengue?
Dengue is anacute febrile illness, often presenting with severe musculoskeletal pain, caused by one of four serotypes of flavivirus.
Incidence: Worldwide, nearly 400 million people have been infected with dengue, but many infections are mild. As urban centers in tropical nations have grown, the number of people at risk for dengue fever and dengue hemorrhagic fever has likewise grown and now approaches 1 billion. Sporadic outbreaks occur in the warmer regions of the U.S., e.g., Texas and Hawaii.
Causes: The disease is transmitted to humans by the bite of the Aedes aegypti mosquito, which is endemic in tropical regions of the world and causes periodic epidemic disease in Southeast Asia, Africa, Mexico, and South and Central America.
Symptoms: Fever without associated features is the most common presentation of dengue. The incubation period of 5 to 7 days precedes sudden onset of fever, myalgia, arthralgias, and headache; a rash may develop 3 days later. Most patients recover uneventfully. Signs and symptoms of grave disease (dengue hemorrhagic fever) include hypothermia, abdominal pain, syncope, and altered mental status. Young children tend to have more serious infections than adults; capillary leak syndromes (with diffuse bleeding) occur in some patients; people with coexisting conditions (such as diabetes mellitus, type AB blood group, malnutrition) are more likely to experience severe disease than others.
Diagnosis: Dengue is usually diagnosed by its clinical presentation in patients living in endemic areas. The diagnosis can be confirmed with dengue-specific IgM antibody testing, which usually becomes detectable between 3 days and two weeks after the onset of disease, followed by a rise in titer of IgG levels. Patients who are reinfected with dengue may have very high levels of dengue-specific IgG antibodies. The responsible virus can be isolated from the serum of infected patients using immunofluorescence or the polymerase chain reaction.
Prevention: People living in or traveling to areas where the Aedes aegypti mosquito is endemic should avoid spending time outdoors around dawn or dusk, when the mosquitoes are most active. They should also apply insect repellents suitable for direct body contact to exposed skin and should impregnate their clothing with insect repellents, such as pyrethrins. Mosquito netting also limits exposure to the mosquito. Nations in which dengue is endemic rely on vector (mosquito) eradication programs when they can afford the necessary infrastructure investments. Despite decades of research, vaccines to prevent dengue have been difficult to develop but may be available around 2020.
Treatment: There are no direct antiviral agents effective against dengue. Supportive care for the patient (rest, hydration, and analgesics) is the only current therapy.
What is schistosomiasis?
Schistosomiasis is any of several parasitic tropical diseases caused by infestation with flukes of the genus Schistosoma that may colonize the urinary tract, mesenteries, liver, spleen, or biliary tree.
Incidence : Although schistosomiasis is rare in the U.S., it is endemic in Asia, Africa, South America, and some Caribbean islands. Nearly 240 million people are affected worldwide, 85% of whom live in Africa. Schistosomiasis ranks second after malaria as a socioeconomic and public health problem in tropical and subtropical areas.
Causes: Infestation occurs by wading or bathing in water contaminated by cercariae that parasitize freshwater snails or bivalve mollusks.
Symptoms: Symptoms include abdominal pain, cough, diarrhea, eosinophilia, fatigue, fever, genital sores (which increase vulnerability to HIV infection), and hepatosplenomegaly.
Diagnosis: Diagnosis is made by enzyme-linked immunosorbent assay (ELISA) or by microscopic identification of eggs in stool or the urine.
Prevention: The best prevention is elimination of the freshwater snails that are the natural reservoir of the disease, for which acrolein (a contact herbicide for controlling algae and submersed and floating weeds), copper sulfate, and niclosamide (a taeniacide) can be used. Snail populations can also be controlled by introducing or increasing crayfish populations.
Treatment: The drug of choice is praziquantel.
What is yellow fever?
Yellow fever is either of two forms of an acute, infectious disease caused by a flavivirus and transmitted by species of the Aedes mosquito. It is endemic in Western Africa, Brazil, and the Amazon region of South America but is no longer present in the U.S. There are two forms of yellow fever: urban, in which the transmission cycle is mosquito to human to mosquito; and sylvan, in which the reservoir is wild primates. According to the World Health Organization, yellow fever afflicts about 200,000 people a year in Africa and South America, about 30,000 of whom die.
Causes: The virus is carried most commonly by the Aedes aegypti mosquito, but the A. vittatus and A. taylori mosquitoes are also important vectors.
Symptoms: After an incubation period of 3 to 6 days, patients develop high fever, headache, muscle aches, nausea and vomiting, and GI disturbances such as diarrhea or constipation. In most patients, the disease resolves in 2 or 3 days, but in about 20% the fever returns after a 1- to 2-day remission and is accompanied by abdominal pain, severe diarrhea, GI bleeding (producing a characteristic black vomit), anuria, and jaundice (hence the name yellow fever) caused by liver infection. Rarely, there is progressive liver failure, renal failure, and death. Yellow fever can be distinguished from dengue by the presence of jaundice, and from malaria by the absence of splenomegaly and low serum transaminase levels. Blood tests can identify the virus and its antigens, to which antibodies are formed in 5 to 7 days. A liver biopsy to isolate the virus is contraindicated because of the risk of bleeding.
Laboratory Findings: As in many viral infections, the white blood cell count and platelet count may be suppressed. The erythrocyte sedimentation rate is rarely elevated. In severely ill patients with jaundice or renal failure, the serum bilirubin and creatinine levels are elevated.
Diagnosis: Diagnosis on clinical grounds alone is almost impossible during the period of infection or in atypical mild forms. Yellow fever viral antigen or antibodies may be detected during the acute phase of the illness.
Prophylaxis: Preventive measures include mosquito control by screening, spraying with nontoxic insecticides, and destruction of breeding areas. Yellow fever vaccine prepared from the 17D strain is available for those who plan to travel or live in areas where the disease is endemic. The vaccine is contraindicated in infants under 4 months old and in women in the first trimester of pregnancy.
Treatment: No antiviral agents are effective against the yellow fever virus. Fluids are given to maintain fluid and electrolyte balance, acetaminophen to reduce fever, and histamine blockers, e.g., ranitidine, or gastric acid pump inhibitors, e.g., omeprazole, to decrease the risk of GI bleeding. Vitamin K is given if there is decreased production of prothrombin by the liver. A live virus vaccine, which can be obtained only at designated vaccination centers, may be given to adults and children over 9 months old who are traveling to countries where yellow fever is endemic; the vaccine is effective for 10 years, after which a booster is required. Those who are immunosuppressed, pregnant, or allergic to eggs should not receive the vaccine. Travelers must determine if the country they are visiting has regulations about vaccination.
What is bacillary angiomatosis?
Bacillary angiomatosis is an acute infectious disease caused by Bartonella quintana or B. henselae. It is characterized by skin lesions that may vary from small papules to pyogenic granulomas or pedunculated masses. These occur anywhere on the skin and may involve mucous membranes. If the lesions ulcerate, they may extend to and destroy underlying bone. In addition, the organisms are disseminated to the liver, spleen, bone marrow, and lymph nodes. In the liver there may be painful, multiple, cystic, blood-filled spaces (peliosis hepatitis). Most patients with this disease are immunocompromised or infected with HIV. In the untreated immunocompetent patient, recovery may be prolonged but is usually complete. In the untreated immunocompromised patient, death is likely. When the organisms are disseminated, treatment for several months with oral doxycycline or oral erythromycin will help alter the course of the disease. Culture of the organism provides diagnosis.
What is leptospirosis?
Leptospirosis is any of several infectious disease affecting humans and domestic animals (fogs, horses, pigs), abused by spirochetes of the genus Leptospira.
What is chancroid?
hancroid is a sexually transmitted infection, caused by the Haemophilus ducreyi (a gram-negative bacillus). Its hallmark is the appearance on the genitals of one or more painful ulcers. The incubation period is typically 2 to 5 days, although longer incubations have been reported. The genital chancre of syphilis is clinically distinguished from that of chancroid in that the syphilitic ulcer is painless. Cultures on chocolate agar are used to confirm the diagnosis. Ceftriaxone, azithromycin, or ciprofloxacin are used to treat the infection.
Symptoms: A chancroid begins with multiple pustules or ulcers having abrupt edges, a rough floor, yellow exudate, and purulent secretion. It is sensitive and inflamed. It heals rapidly, leaving a scar. Chancroids may affect the penis, urethra, vulva, or anus. Multiple lesions may develop by autoinoculation. Types include transient, phagedenic, giant, and serpiginous.
What is lymphogranuloma venereum (LGV)?
Lymphogranuloma venereum (LGV) is asexually transmitted cause of genital ulcer disease and proctitis.
Incidence: LGV infections are reported in about 300 people a year in the U.S. The disease is more common in those infected with HIV and in men who have sex with other men.
Causes LGV is caused by Chlamydia trachomatis.
Symptoms: Infection can cause a painless red erosion on the genitals or rectum, followed approx. 1 to 2 weeks later by buboes (enlargements of the inguinal lymph node). Buboes may obstruct lymphatic channels or cause fistulous tracts to neighboring tissues if the infection is not treated. However, because many men and more women do not recognize early symptoms, the disease may spread from person-to-person and proliferate inside the infected individual, with severe consequences. Symptomatic patients may develop ulcerating vesicles on the genitals, urethral inflammation, abdominal pain, and swollen lymph nodes in the groin and rectum; men often have inflamed and swollen testicles. Approx. 40% of women develop chronic pelvic inflammatory disease (PID), leading to chronic pain, infertility, and an increased risk of having a tubal pregnancy. Spread of the disease into perirectal lymph nodes may cause scarring and rectal obstruction.
Diagnosis: The CDC recommends that all sexually active women under 20 years old be screened yearly for chlamydia; sexually active women over the age of 20 with multiple sex partners who do not use condoms should also be screened yearly. Swabs taken from genital tissues (or from genital ulcers) are sent for nucleic acid amplification testing, immunofluorescence, or microbiologic cultures, although the latter are relatively insensitive.
Prevention: Safe sexual practices prevent infection with LGV.
Treatment: The disease can be treated effectively with a 3-week course of doxycline or azithromyocin; erythromycin is used for pregnant woman. Recurrent infection is common if barrier contraception is not used during intercourse.
What is Q fever?
Q fever is an acute infectious disease characterized by headache, fever, severe sweating, malaise, myalgia, and anorexia. Q fever is caused by the rickettsia, Coxiella burnetii, an intracellular, gram-negative bacterium, and is contracted by inhaling infected dust, drinking unpasteurized milk from infected animals, or handling infected animals such as goats, cows, or sheep. Transmission by human contact is rare but has occurred. An effective vaccine is available for the prevention of infection for those who have a good chance of being exposed to the disease. Tetracyclines are used to treat the infection.
Treatment: Like other ricksettsial diseases, Q fever is treated with oral doxycycline.
What is brucellosis?
Brucellosis is a widespread infectious disease affecting cattle, swine, goats, other animals, and sometimes humans, caused by bacteria of several Brucella spp. In humans it is an influenza-like illness, with fevers, chills, headache, and body aches. It is a rare cause of endocarditis. It occurs most often in ranchers, veterinarians, and those who consume unpasteurized dairy products.
Treatment: In adults, treatment consists of doxycycline and rifampin, or doxcycline and an aminoglycoside, for 6 weeks. In children and pregnant women, tetracyclines should be avoided because they damage developing teeth and bones.
What is tularemia?
Tularemia is an acute plaguelike infectious disease caused by Francisella tularensis. It is transmitted to humans by the bite of an infected tick or other bloodsucking insect, by direct contact with infected animals, by eating inadequately cooked meat, or by drinking water that contains the organism. Streptomycin or gentamicin is effective in treating the disease.
Symptoms: The incubation period is 2 to 10 days; symptoms include headache, fever, chills, vomiting, and body aches.
What is toxic shock syndrome?
Toxic shock syndrome is a life-threatening disorder caused by an exotoxin produced by certain strains of Staphylococcus aureus and group A streptococci. It was originally described in young women using vaginal tampons but has also been reported in users of contraceptive sponges and diaphragms, in burn patients, patients with cellulitis, and after surgical wound packing. The disease is fatal in roughly 5–50% of cases.
Symptoms: The diagnosis is made when the following criteria are met: fever of 102F (38.9C) or greater; diffuse, macular (flat), erythematous rash (resembling a sunburn), followed in 1or 2 weeks by peeling of the skin, particularly of the palms and soles; hypotension or orthostatic syncope; and involvement of three or more of the following organ systems: gastrointestinal (vomiting or diarrhea at the onset of illness), muscular (severe myalgia), mucous membrane (vaginal, oropharyngeal, or conjunctival) hyperemia, renal, hepatic, hematological (platelets less than 100,000/mm3), and central nervous system (disorientation or alteration in consciousness without focal neurological signs when fever and hypotension are absent). Results of blood, throat, and cerebrospinal fluid cultures are usually negative. The possibility of Rocky Mountain spotted fever, leptospirosis, or rubeola should be eliminated by blood tests.
Diagnosis: The diagnosis is based on observation of typical signs and symptoms. There is no definitive laboratory or radiologic diagnostic test result.
Prevention: Menstrual tampons should be removed and replaced frequently and ultra-absorbent tampons should be avoided. Wound packing should be removed as often as is feasible (typically daily).
Treatment: Penicillinase-resistant antibiotics such as nafcillin or oxacillin do not affect the initial syndrome but may prevent its recurrence. Patients who develop multiorgan system failure (such as kidney failure) may need supportive care that includes kidney dialysis, or ventilatory support for acute respiratory distress syndrome.
What is cysticercosis?
Cysticersosis is an infestation with the larvae of the pork tapeworm. It occurs when ingested Taenia solium larvae from uncooked pork burrow through the intestinal wall and are carried to other tissues through the blood. They may encyst in the heart, eyes, muscles, or brain. In the brain, they may cause a wide variety of neurological symptoms, including seizures. A patient history of eating undercooked pork or other meats may be helpful in establishing the diagnosis, esp. in adults with new-onset seizures who are found to have multiple cystic lesions in the brain.
Treatment: Anticonvulsants are used to control seizures. Antiparasitic drugs such as praziquantel or albendazole are effective.
Venes, Donald. Taber’s Cyclopedic Medical Dictionary (p. 618). F.A. Davis Company. Kindle Edition.
What is Legionnaires’ disease?
Legionnaires’ disease is a severe, sometimes fatal disease characterized by pneumonia, dry cough, myalgia, and sometimes gastrointestinal symptoms. It may occur in epidemics or sporadically and is an important cause of nosocomial pneumonia because health care associated legionellosis, while rare, is more likely to be fatal than legionellosis acquired in the community at large.
Incidence: Approximately 8,000–18,000 people are infected each year in the U.S. Those at risk include middle-aged or older adults who smoke cigarettes or have chronic lung disease and those whose immune systems are compromised by diabetes, renal failure, organ transplantation, cancer, or AIDS. The disease is responsible for about 5% of all pneumonias.
Causes: The infection is caused by bacteria of the genus Legionella. The bacteria may be inhaled or aspirated from contaminated water supplies, e.g., water cooling towers, humidifiers, air conditioning vents, hot water tanks, whirlpools, spas, showers, hydrotherapy tanks, public water fountains, and indoor waterfalls, or contaminated respiratory therapy equipment or nasogastric tubes. It thrives at temperatures about 90–105F (32–41C). Two distinct diseases occur from the various Legionella species: Legionnaires’ disease or a milder influenza-like illness known as Pontiac fever.
Symptoms: The signs and symptoms of Legionnaire’s disease are similar to those of other pneumonias. Fatigue, anorexia, headache, malaise, myalgia, and diarrhea also may be present. The incubation period is 2 to 10 days.
Diagnosis: It is diagnosed by culturing sputum or bronchial washings and growing the bacteria on a special medium (such as buffered charcoal yeast extract agar) and carbolfuchin or silver staining; the bacteria can also be identified by blood serology for antibody titer or by antigen testing of urine.
Treatment: Erythromycin given early in the course of the disease and for a prolonged period is the treatment of choice. Rifampin may also be given as an adjunct but should not be used alone. Other macrolides, e.g., clarithromycin and azithromycin, and fluoroquinolones are effective therapeutic options.
Venes, Donald. Taber’s Cyclopedic Medical Dictionary (p. 1400). F.A. Davis Company. Kindle Edition.
What is Pontiac fever?
Pontiac fever is an infection with Legionella species that causes fevers, chills, headache, gastrointestinal upset, and prostration, but not pneumonia.
