Orris

Class1: typhoid Class 2: cholera, salmonellosis, dehydration shock Class 3: shigela, helmintheasis Class 4: influenza, parainfluenza, diphtheria Class 5: hepatitis A,B and HIV infection Class 6: maleria, lime disease, plague Class 7 leptospirosis In conspect write 1-2 pages about 1 disease. Definition, etiology, pathogenesis, clinical feature, incubation peroid, complication, lab diagnosis, treatment All points mentioned correctly

Reading File
Reading File
Finding Sources
Searching PubMed

infectious diseases

Searching the Web

WHO infectious diseases fact sheets typhoid cholera influenza hepatitis malaria

Your classes can be organized as follows:
  1. Class 1: Typhoid fever
  2. Class 2: Cholera, salmonellosis, dehydration and hypovolemic shock
  3. Class 3: Shigellosis, helminthiasis
  4. Class 4: Influenza, parainfluenza, diphtheria
  5. Class 5: Hepatitis A, hepatitis B, HIV infection
  6. Class 6: Malaria, Lyme disease, plague
  7. Class 7: Leptospirosis
For each disease, a 1 to 2 page conspect can follow this structure:
  1. Definition
  2. Etiology
  3. Pathogenesis
  4. Incubation period
  5. Clinical features
  6. Complications
  7. Laboratory diagnosis
  8. Treatment
The disease names corrected for spelling are: shigellosis (not “shigela”), helminthiasis, malaria, and Lyme disease. “Dehydration shock” is more accurately called hypovolemic shock due to severe dehydration.
Which one disease should I write first as a complete 1 to 2 page conspect?

All in sequence

Reading File
This is a full multi-disease study set, so I will prepare it in sequence, one class at a time, with each disease using the same eight headings.

Topic map

  1. Class 1: Typhoid fever
  2. Class 2: Cholera, salmonellosis, severe dehydration and hypovolemic shock
  3. Class 3: Shigellosis, helminthiasis
  4. Class 4: Influenza, parainfluenza, diphtheria
  5. Class 5: Hepatitis A, hepatitis B, HIV infection
  6. Class 6: Malaria, Lyme disease, plague
  7. Class 7: Leptospirosis
Because a 1 to 2 page conspect for every listed disease would be very long, I will give detailed, exam-ready notes class by class. We start with typhoid fever, then continue in the order listed.
Asking for Preferences

Which section should I write in full first?

Your classes can be organized as follows:
  1. Class 1: Typhoid fever
  2. Class 2: Cholera, salmonellosis, dehydration and hypovolemic shock
  3. Class 3: Shigellosis, helminthiasis
  4. Class 4: Influenza, parainfluenza, diphtheria
  5. Class 5: Hepatitis A, hepatitis B, HIV infection
  6. Class 6: Malaria, Lyme disease, plague
  7. Class 7: Leptospirosis
For each disease, a 1 to 2 page conspect can follow this structure:
  1. Definition
  2. Etiology
  3. Pathogenesis
  4. Incubation period
  5. Clinical features
  6. Complications
  7. Laboratory diagnosis
  8. Treatment
The disease names corrected for spelling are: shigellosis (not “shigela”), helminthiasis, malaria, and Lyme disease. “Dehydration shock” is more accurately called hypovolemic shock due to severe dehydration.
Which one disease should I write first as a complete 1 to 2 page conspect?This is a full multi-disease study set, so I will prepare it in sequence, one class at a time, with each disease using the same eight headings.

Topic map

  1. Class 1: Typhoid fever
  2. Class 2: Cholera, salmonellosis, severe dehydration and hypovolemic shock
  3. Class 3: Shigellosis, helminthiasis
  4. Class 4: Influenza, parainfluenza, diphtheria
  5. Class 5: Hepatitis A, hepatitis B, HIV infection
  6. Class 6: Malaria, Lyme disease, plague
  7. Class 7: Leptospirosis
Because a 1 to 2 page conspect for every listed disease would be very long, I will give detailed, exam-ready notes class by class. We start with typhoid fever, then continue in the order listed.
Finding Sources
Searching PubMed

typhoid fever

Searching the Web

WHO typhoid fact sheet treatment diagnosis antimicrobial resistance

Your classes can be organized as follows:
  1. Class 1: Typhoid fever
  2. Class 2: Cholera, salmonellosis, dehydration and hypovolemic shock
  3. Class 3: Shigellosis, helminthiasis
  4. Class 4: Influenza, parainfluenza, diphtheria
  5. Class 5: Hepatitis A, hepatitis B, HIV infection
  6. Class 6: Malaria, Lyme disease, plague
  7. Class 7: Leptospirosis
For each disease, a 1 to 2 page conspect can follow this structure:
  1. Definition
  2. Etiology
  3. Pathogenesis
  4. Incubation period
  5. Clinical features
  6. Complications
  7. Laboratory diagnosis
  8. Treatment
The disease names corrected for spelling are: shigellosis (not “shigela”), helminthiasis, malaria, and Lyme disease. “Dehydration shock” is more accurately called hypovolemic shock due to severe dehydration.
Which one disease should I write first as a complete 1 to 2 page conspect?This is a full multi-disease study set, so I will prepare it in sequence, one class at a time, with each disease using the same eight headings.

Topic map

  1. Class 1: Typhoid fever
  2. Class 2: Cholera, salmonellosis, severe dehydration and hypovolemic shock
  3. Class 3: Shigellosis, helminthiasis
  4. Class 4: Influenza, parainfluenza, diphtheria
  5. Class 5: Hepatitis A, hepatitis B, HIV infection
  6. Class 6: Malaria, Lyme disease, plague
  7. Class 7: Leptospirosis
Because a 1 to 2 page conspect for every listed disease would be very long, I will give detailed, exam-ready notes class by class. We start with typhoid fever, then continue in the order listed.

Quick answer

Class 1: Typhoid Fever

Definition: A systemic bacterial infection, also called enteric fever, caused mainly by Salmonella enterica serovar Typhi. It is transmitted by the fecal-oral route.
Etiology: Salmonella Typhi, a Gram-negative motile bacillus. Humans are the only reservoir. Infection follows ingestion of food or water contaminated with feces or urine from an infected person or chronic carrier.
Pathogenesis: The organisms enter through the intestine, invade Peyer patches in the ileum, survive within macrophages, and spread through lymphatics and blood. They multiply in the liver, spleen, bone marrow, gallbladder, and reticuloendothelial system. Re-entry into the intestine may cause ulceration of Peyer patches.
Incubation period: Usually 6-30 days, commonly 8-14 days.
Clinical features: Gradually rising fever, headache, malaise, anorexia, abdominal discomfort, constipation early in illness or diarrhea later, dry cough, coated tongue, hepatosplenomegaly, and relative bradycardia. Rose spots may appear on the trunk. Severe disease may cause delirium or altered sensorium.
Complications: Intestinal hemorrhage, ileal perforation, peritonitis, encephalopathy, myocarditis, hepatitis, cholecystitis, pneumonia, shock, relapse, and chronic carrier state.
Laboratory diagnosis: Blood culture is most useful during the first week. Bone marrow culture is highly sensitive, even after antibiotics. Stool and urine cultures may become positive later. CBC may show leukopenia. Widal test has limited specificity and should not be the sole diagnostic test.
Treatment: Oral or intravenous rehydration, nutrition, antipyretics, and antibiotics guided by local susceptibility. Common options include ceftriaxone, azithromycin, or cefixime for uncomplicated disease where appropriate. Fluoroquinolones should only be used if susceptibility is proven because resistance is common. Treat complications urgently, especially intestinal perforation. Prevention includes safe water, sanitation, hand hygiene, food safety, and typhoid vaccination.

Class 2: Cholera

Definition: An acute secretory diarrheal illness caused by toxigenic Vibrio cholerae, leading to rapid dehydration.
Etiology: Mainly Vibrio cholerae serogroups O1 and O139. Transmission occurs through contaminated water or food.
Pathogenesis: Bacteria colonize the small intestine and produce cholera toxin. The toxin increases cyclic AMP in intestinal epithelial cells, causing massive secretion of chloride, bicarbonate, sodium, potassium, and water into the intestinal lumen.
Incubation period: A few hours to 5 days, usually 2-3 days.
Clinical features: Sudden onset of profuse painless watery diarrhea, classically “rice-water” stools, vomiting, thirst, muscle cramps, weakness, sunken eyes, dry mouth, reduced urine output, tachycardia, hypotension, and severe dehydration. Fever is usually absent.
Complications: Severe dehydration, hypovolemic shock, acute kidney injury, hypokalemia, metabolic acidosis, arrhythmias, coma, and death.
Laboratory diagnosis: Clinical diagnosis is important during outbreaks. Stool microscopy may show darting motility. Stool culture on selective media confirms infection. Rapid antigen tests or PCR may be used where available. Check electrolytes, renal function, and acid-base status in severe cases.
Treatment: Immediate fluid replacement is the priority. Give oral rehydration solution for mild or moderate dehydration. Give rapid intravenous Ringer lactate for severe dehydration or shock. Continue feeding and give zinc to children. Antibiotics can shorten illness and reduce bacterial shedding in severe cases, based on local resistance patterns. Prevention includes safe water, sanitation, hand washing, food hygiene, and oral cholera vaccines.

Class 2: Salmonellosis

Definition: Gastrointestinal infection caused by non-typhoidal Salmonella species, usually resulting in acute gastroenteritis.
Etiology: Common organisms include Salmonella Enteritidis and Salmonella Typhimurium. Sources include contaminated poultry, eggs, meat, unpasteurized milk, reptiles, and contaminated water.
Pathogenesis: Organisms invade intestinal mucosa, producing inflammation and fluid secretion. In vulnerable people, bacteria may enter the bloodstream and cause invasive disease.
Incubation period: Usually 6-72 hours, commonly 12-36 hours.
Clinical features: Acute fever, nausea, vomiting, abdominal cramps, watery or sometimes bloody diarrhea, headache, and malaise. Illness commonly resolves within 4-7 days.
Complications: Dehydration, bacteremia, sepsis, focal infections such as osteomyelitis or endovascular infection, reactive arthritis, and severe disease in infants, elderly people, and immunocompromised patients.
Laboratory diagnosis: Stool culture or PCR. Blood cultures are needed if invasive infection or sepsis is suspected. Assess dehydration, electrolytes, and renal function in severe illness.
Treatment: Oral fluids and electrolyte replacement are usually sufficient. Antibiotics are not routinely needed in uncomplicated gastroenteritis because they may prolong carriage. Use antibiotics for severe illness, bacteremia, extraintestinal infection, infants, elderly people, or immunocompromised patients, guided by susceptibility testing.

Class 2: Severe Dehydration and Hypovolemic Shock

Definition: Severe dehydration is a major loss of body water and electrolytes. Hypovolemic shock occurs when reduced circulating blood volume causes inadequate tissue perfusion.
Etiology: Severe diarrhea, vomiting, cholera, bleeding, burns, fever, poor fluid intake, diabetic emergencies, and excessive urine loss.
Pathogenesis: Fluid loss decreases intravascular volume, venous return, cardiac output, and tissue oxygen delivery. The body initially compensates with tachycardia and vasoconstriction. Untreated shock causes organ failure.
Clinical features: Intense thirst, dry mucous membranes, sunken eyes, poor skin turgor, lethargy, cold extremities, weak rapid pulse, low blood pressure, delayed capillary refill, oliguria or anuria, confusion, and loss of consciousness.
Complications: Acute kidney injury, severe metabolic acidosis, electrolyte disturbances, arrhythmias, ischemic organ injury, disseminated intravascular coagulation, coma, and death.
Laboratory diagnosis: Clinical assessment is urgent. Serum electrolytes, blood glucose, urea, creatinine, venous or arterial blood gas, lactate, CBC, and tests to identify the cause.
Treatment: Airway, breathing, circulation. Establish intravenous access and give rapid isotonic crystalloid, preferably Ringer lactate in diarrheal dehydration. Monitor pulse, blood pressure, mental status, urine output, and electrolytes. Treat the cause, such as cholera, hemorrhage, sepsis, or diabetic ketoacidosis.

Class 3: Shigellosis

Definition: Acute invasive bacterial diarrhea caused by Shigella species.
Etiology: Shigella sonnei, S. flexneri, S. boydii, and S. dysenteriae. Transmission is fecal-oral, often person-to-person, through contaminated food, water, or hands.
Pathogenesis: Shigella invades colonic epithelial cells and causes intense inflammation, ulceration, and mucosal destruction. S. dysenteriae type 1 may produce Shiga toxin.
Incubation period: Usually 1-3 days.
Clinical features: Fever, abdominal cramps, urgency to defecate, tenesmus, and frequent small-volume stools containing mucus and blood. Children may develop seizures due to high fever.
Complications: Severe dehydration, toxic megacolon, rectal prolapse, intestinal perforation, hemolytic uremic syndrome, seizures, encephalopathy, and reactive arthritis.
Laboratory diagnosis: Stool microscopy may reveal leukocytes and red blood cells. Stool culture or PCR confirms the diagnosis. Test antibiotic susceptibility because antimicrobial resistance is common.
Treatment: Oral or intravenous rehydration, continued feeding, and infection-control measures. Antibiotics are used for severe disease, high-risk patients, or outbreaks, according to local susceptibility. Avoid antimotility drugs in bloody diarrhea or suspected dysentery.

Class 3: Helminthiasis

Definition: Infection caused by parasitic worms, including roundworms, tapeworms, flukes, hookworms, and pinworms.
Etiology: Common helminths include Ascaris lumbricoides, hookworms, Trichuris trichiura, Enterobius vermicularis, Taenia species, and Schistosoma species. Transmission may occur through contaminated soil, food, water, undercooked meat, or skin penetration.
Pathogenesis: Disease results from worm migration, tissue invasion, nutrient competition, intestinal obstruction, blood loss, inflammation, or immune reactions. Hookworms can cause chronic intestinal blood loss and anemia.
Incubation period: Variable, from days to weeks or months, depending on the parasite.
Clinical features: May be asymptomatic. Possible features include abdominal pain, diarrhea, nausea, weight loss, malnutrition, anemia, cough during larval lung migration, pruritus ani in pinworm infection, and visible worms in stool.
Complications: Iron-deficiency anemia, malnutrition, growth delay, intestinal obstruction, biliary obstruction, pancreatitis, seizures in neurocysticercosis, and organ damage in schistosomiasis.
Laboratory diagnosis: Stool examination for ova and parasites, tape test for pinworm, eosinophilia, antigen tests, serology, and imaging where tissue infection is suspected.
Treatment: Depends on the parasite. Albendazole or mebendazole is commonly used for many intestinal nematodes. Praziquantel is used for many tapeworm and fluke infections. Correct anemia and malnutrition. Prevention includes sanitation, footwear, safe food and water, hand hygiene, and periodic deworming in endemic settings.

Class 4: Influenza

Definition: An acute viral respiratory infection caused by influenza viruses.
Etiology: Influenza A and B cause seasonal epidemics. Influenza A can cause pandemics because of antigenic variation.
Pathogenesis: The virus infects respiratory epithelial cells, causing cell damage, inflammation, and systemic cytokine-mediated symptoms.
Incubation period: Usually 1-4 days, commonly about 2 days.
Clinical features: Sudden fever, chills, headache, myalgia, fatigue, sore throat, dry cough, rhinorrhea, and malaise. Children may have vomiting or diarrhea.
Complications: Viral pneumonia, secondary bacterial pneumonia, acute respiratory distress syndrome, myocarditis, encephalitis, worsening of asthma or COPD, otitis media, and death in high-risk groups.
Laboratory diagnosis: Clinical diagnosis during outbreaks may be sufficient. Rapid antigen tests, rapid molecular assays, and RT-PCR can confirm infection.
Treatment: Rest, fluids, antipyretics, and isolation while infectious. Antiviral treatment such as oseltamivir is most useful when started early and is especially indicated for severe, hospitalized, or high-risk patients. Annual influenza vaccination is the main preventive measure.

Class 4: Parainfluenza

Definition: Viral respiratory infection caused by human parainfluenza viruses, commonly causing croup in young children.
Etiology: Human parainfluenza viruses types 1-4, belonging to the Paramyxoviridae family.
Pathogenesis: The virus infects respiratory epithelium. In children, inflammation and edema of the larynx and subglottic region cause airway narrowing and croup.
Incubation period: Usually 2-6 days.
Clinical features: Fever, runny nose, cough, hoarseness, and sore throat. Croup causes barking cough, inspiratory stridor, and respiratory distress. It may also cause bronchiolitis or pneumonia.
Complications: Severe upper-airway obstruction, hypoxia, secondary bacterial infection, and respiratory failure in severe croup.
Laboratory diagnosis: Usually clinical. PCR from a nasopharyngeal specimen can identify the virus but is not routinely necessary.
Treatment: Supportive care, fluids, and antipyretics. Croup is treated with corticosteroids such as dexamethasone. Nebulized epinephrine is used for moderate or severe croup with stridor at rest. Severe airway obstruction requires hospital care.

Class 4: Diphtheria

Definition: An acute toxin-mediated infection caused by toxigenic Corynebacterium diphtheriae, usually affecting the upper respiratory tract.
Etiology: Corynebacterium diphtheriae, a Gram-positive bacillus. Transmission occurs through respiratory droplets and close contact.
Pathogenesis: The organism colonizes the throat and produces exotoxin. The toxin inhibits protein synthesis and causes tissue necrosis. A thick adherent gray pseudomembrane forms. Absorbed toxin can damage the heart and nerves.
Incubation period: Usually 2-5 days.
Clinical features: Sore throat, fever, malaise, cervical lymphadenopathy, hoarseness, difficulty swallowing, and a gray-white pseudomembrane over the tonsils, pharynx, or larynx. Neck swelling may produce a “bull neck” appearance.
Complications: Airway obstruction, myocarditis, arrhythmias, heart failure, cranial neuropathies, peripheral neuropathy, renal failure, and death.
Laboratory diagnosis: Take a throat or nasal swab from the edge of the pseudomembrane before antibiotics if possible. Culture and toxigenicity testing confirm disease. Do not wait for laboratory confirmation before treatment.
Treatment: Immediate diphtheria antitoxin plus antibiotics, usually erythromycin or penicillin. Isolate the patient and provide airway support if needed. Close contacts require assessment, prophylactic antibiotics, and vaccination. Prevention is by diphtheria toxoid vaccination.

Class 5: Hepatitis A

Definition: Acute viral inflammation of the liver caused by hepatitis A virus, usually self-limited.
Etiology: Hepatitis A virus, transmitted by the fecal-oral route through contaminated food, water, or close contact.
Pathogenesis: The virus reaches the liver through the bloodstream and replicates in hepatocytes. Liver damage is mainly immune mediated.
Incubation period: About 15-50 days, average 28-30 days.
Clinical features: Fever, fatigue, anorexia, nausea, vomiting, right upper abdominal discomfort, dark urine, pale stool, jaundice, pruritus, and hepatomegaly. Children may have mild or asymptomatic infection.
Complications: Usually none. Rare complications include fulminant hepatic failure, prolonged cholestasis, and relapsing hepatitis.
Laboratory diagnosis: Elevated ALT and AST, bilirubin elevation, and positive serum anti-HAV IgM indicate acute infection. Anti-HAV IgG indicates immunity from past infection or vaccination.
Treatment: Supportive care, adequate fluids and nutrition, avoidance of alcohol and hepatotoxic drugs, and monitoring for acute liver failure. Prevention is by vaccination, safe water, sanitation, and hand hygiene.

Class 5: Hepatitis B

Definition: Viral infection of the liver caused by hepatitis B virus. It can be acute or chronic and may lead to cirrhosis and hepatocellular carcinoma.
Etiology: Hepatitis B virus, transmitted through blood, sexual contact, needles, perinatal exposure, and contaminated instruments.
Pathogenesis: HBV infects hepatocytes. Liver injury is largely caused by the host immune response. Persistent infection can lead to chronic inflammation, fibrosis, cirrhosis, and liver cancer.
Incubation period: Usually 30-180 days, average about 90 days.
Clinical features: Many cases are asymptomatic. Acute disease may cause fatigue, anorexia, nausea, vomiting, fever, arthralgia, dark urine, pale stool, jaundice, and hepatomegaly. Chronic infection may remain silent until cirrhosis develops.
Complications: Chronic hepatitis, cirrhosis, portal hypertension, liver failure, hepatocellular carcinoma, and extrahepatic manifestations such as polyarteritis nodosa.
Laboratory diagnosis: HBsAg indicates current infection. Anti-HBc IgM suggests acute infection. HBeAg often indicates high viral replication. HBV DNA quantifies viral load. Liver enzymes and ultrasound assess liver involvement.
Treatment: Acute infection is usually managed supportively. Severe acute hepatitis may require specialist care. Chronic hepatitis B may be treated with antiviral agents such as tenofovir or entecavir, depending on viral load, ALT, fibrosis, and clinical assessment. Vaccination prevents infection.

Class 5: HIV Infection

Definition: A chronic infection caused by human immunodeficiency virus, which progressively weakens the immune system by destroying CD4 T lymphocytes.
Etiology: HIV-1 is the most common worldwide; HIV-2 is less transmissible and less aggressive. Transmission occurs by sexual contact, blood exposure, shared needles, and mother-to-child transmission.
Pathogenesis: HIV enters CD4 cells using CD4 receptors and co-receptors, replicates within them, and progressively reduces CD4 cell count. Severe immune deficiency leads to opportunistic infections and malignancies.
Incubation period: Acute HIV symptoms may occur 2-4 weeks after infection. Untreated infection may progress to AIDS over years.
Clinical features: Acute infection may cause fever, rash, sore throat, lymphadenopathy, myalgia, headache, mouth ulcers, and diarrhea. Chronic infection may be asymptomatic. Advanced disease causes weight loss, persistent fever, recurrent infections, oral candidiasis, tuberculosis, pneumocystis pneumonia, and other opportunistic diseases.
Complications: AIDS-defining opportunistic infections, tuberculosis, cancers such as Kaposi sarcoma and lymphoma, HIV-associated neurocognitive disorder, kidney disease, and wasting syndrome.
Laboratory diagnosis: Fourth-generation HIV antigen-antibody tests are used for screening. Positive tests require confirmatory testing according to national algorithms. HIV viral load monitors treatment. CD4 count assesses immune status.
Treatment: Start combination antiretroviral therapy as soon as possible after diagnosis. A common regimen includes an integrase inhibitor plus two nucleoside reverse-transcriptase inhibitors. Prevent and treat opportunistic infections, offer vaccinations, provide counseling, and use measures to prevent transmission.

Class 6: Malaria

Definition: A mosquito-borne parasitic disease caused by Plasmodium species.
Etiology: Plasmodium falciparum, P. vivax, P. ovale, P. malariae, and P. knowlesi. It is transmitted mainly by the bite of infected female Anopheles mosquitoes.
Pathogenesis: Sporozoites enter the liver, multiply, and release merozoites into blood. Merozoites infect red blood cells, causing cyclic fever and hemolysis. P. falciparum can cause sequestration of infected cells in small vessels, producing severe organ disease.
Incubation period: Usually 7-30 days, depending on species and immunity.
Clinical features: Fever, chills, sweating, headache, malaise, myalgia, nausea, vomiting, anemia, jaundice, and splenomegaly. Fever may become periodic.
Complications: Cerebral malaria, severe anemia, hypoglycemia, metabolic acidosis, acute kidney injury, pulmonary edema, shock, bleeding, and death. Severe malaria is most commonly caused by P. falciparum.
Laboratory diagnosis: Thick and thin peripheral blood smears are the standard diagnostic tests. Rapid diagnostic tests detect parasite antigens. Repeat testing may be needed if the first smear is negative but suspicion remains high.
Treatment: Treatment depends on species, severity, location of acquisition, pregnancy, and drug resistance. Uncomplicated malaria is often treated with artemisinin-based combination therapy. Severe malaria requires urgent intravenous artesunate and intensive supportive care. P. vivax and P. ovale require treatment for liver hypnozoites after testing for G6PD deficiency.

Class 6: Lyme Disease

Definition: A tick-borne infection caused by Borrelia species, mainly Borrelia burgdorferi.
Etiology: Transmitted through bites of infected Ixodes ticks.
Pathogenesis: The spirochete spreads from the skin through blood and tissues, affecting joints, nervous system, heart, and skin.
Incubation period: Usually 3-30 days.
Clinical features: Early localized disease causes erythema migrans, an expanding red rash sometimes with central clearing, fever, fatigue, headache, and myalgia. Later disease may cause facial nerve palsy, meningitis, radiculopathy, carditis, palpitations, and intermittent arthritis, especially of the knee.
Complications: Lyme carditis with heart block, neurologic disease, recurrent arthritis, and persistent symptoms after appropriate treatment in some patients.
Laboratory diagnosis: Typical erythema migrans is diagnosed clinically. Other cases are evaluated with two-tier serologic testing: a screening antibody test followed by a confirmatory test. PCR may help in selected cases, such as synovial fluid in Lyme arthritis.
Treatment: Early uncomplicated disease is commonly treated with doxycycline, amoxicillin, or cefuroxime. Intravenous ceftriaxone may be needed for severe neurologic disease or significant carditis. Tick avoidance and prompt tick removal help prevention.

Class 6: Plague

Definition: A severe zoonotic infection caused by Yersinia pestis.
Etiology: Yersinia pestis, a Gram-negative coccobacillus. It is transmitted mainly by flea bites from infected rodents. Pneumonic plague can spread by respiratory droplets.
Pathogenesis: The organism enters through skin or lungs, multiplies in lymph nodes and blood, and may cause sepsis, disseminated intravascular coagulation, and multiorgan failure.
Incubation period: Usually 2-6 days for bubonic plague. Pneumonic plague may develop within 1-4 days.
Clinical features: Bubonic plague causes sudden fever, chills, headache, weakness, and painful swollen lymph nodes called buboes. Septicemic plague causes shock, abdominal pain, bleeding, and necrosis of fingers or toes. Pneumonic plague causes cough, chest pain, dyspnea, hemoptysis, and rapidly progressive respiratory failure.
Complications: Septic shock, disseminated intravascular coagulation, gangrene, meningitis, acute respiratory failure, and death.
Laboratory diagnosis: Culture and PCR of bubo aspirate, blood, sputum, or cerebrospinal fluid as appropriate. Inform the laboratory when plague is suspected because special handling is necessary.
Treatment: Begin antibiotics immediately if suspected. Gentamicin, streptomycin, doxycycline, ciprofloxacin, or other appropriate agents may be used according to local protocols. Pneumonic plague requires respiratory isolation and contact prophylaxis.

Class 7: Leptospirosis

Definition: A zoonotic bacterial infection caused by Leptospira species, ranging from mild fever to severe multiorgan disease.
Etiology: Leptospira interrogans and related species. Infection occurs through contact of broken skin, mucous membranes, or conjunctiva with water or soil contaminated by urine of infected animals, especially rats, dogs, cattle, and pigs.
Pathogenesis: Spirochetes enter the bloodstream and disseminate to the liver, kidneys, lungs, muscles, and central nervous system. Endothelial injury, inflammation, and immune responses cause organ dysfunction.
Incubation period: Usually 2-30 days, commonly 5-14 days.
Clinical features: Sudden fever, severe headache, chills, myalgia especially calf tenderness, conjunctival suffusion, nausea, vomiting, abdominal pain, and rash. Severe disease, called Weil disease, causes jaundice, renal failure, bleeding, meningitis, and respiratory distress.
Complications: Acute kidney injury, jaundice, hepatitis, pulmonary hemorrhage, myocarditis, arrhythmias, meningitis, shock, and multiorgan failure.
Laboratory diagnosis: CBC may show thrombocytopenia. Liver and renal function tests may be abnormal. PCR is useful early in infection. Serologic testing, especially IgM and microscopic agglutination testing, supports diagnosis later. Culture is slow and not usually used for urgent diagnosis.
Treatment: Mild disease may be treated with doxycycline or amoxicillin according to local guidelines. Severe disease requires hospital admission and intravenous antibiotics such as penicillin or ceftriaxone, plus fluid management, renal support, and treatment of pulmonary hemorrhage or shock. Prevention includes protective clothing, rodent control, safe water, and avoiding contact with contaminated floodwater.
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