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Vessels resemble blood capillaries, but larger • Carry almost colorless lymph; comes from plasma
• Seeps through capillaries to become interstitial fluid surrounding tissue cells, which it bathes, feeds
• Easily permeable, takes up foreign material • One-way valves, contraction of vessel walls,
compression by body's muscles maintain flow to multiple lymph nodes
• Contain phagocytic cells and lymphocytes to trap, destroy foreign material such as microbial cells
• Lymph flows out of nodes through vessels that combine into one large tube, the thoracic duct
• Discharges into large subclavian vein behind left collarbone, back into main blood circulation
• Infection of limb may result in visible red streak spreading from infection site called lymphangitis
• Blood, lymph both carry leukocytes, antimicrobial proteins (antibodies, complement, lysozyme, interferon); inflammatory response may cause vessels to clot • Following flea bite, symptoms appear within 2-6 days
- Enlarged and tender lymph nodes called buboes
- High fever, shock, delirium, patchy bleeding under skin
• Following inhalation of respiratory droplets from infected patient or animal, pneumonic plague may develop
- Cough, bloody sputum arise within 1-3 days • If spread by bloodstream, septicemic plague may develop
- Endotoxin released causes shock, also disseminated intravascular coagulation, which causes bleeding into skin and organs, produces red or black patchy rash • Many cases asymptomatic or subclinical
• If occur, begin with sudden onset of fever for 2-7 days
- May recur 12-24 hours later (biphasic fever) • Headache, joint and muscle pain, pain behind eyes, maculopapular rash that may later become hemorrhagic, with development of petechiae
- Rash does not appear in mild cases, often leading to misdiagnosis of influenza or other viral disease
• Mild mucosal bleeding may occur in nose or gums
• Sore throat, abdominal pain, vomiting, diarrhea may occur
• Usually self-limiting, rarely fatal
• Dengue hemorrhagic fever (DHF) can occur in second infection, may lead to dengue shock syndrome (DSS)
- Weak, rapid pulse, moist skin, restlessness, low blood pressure, bleeding in form of petechiae, easy bruising
- Massive gastrointestinal, vaginal bleeding may occur
- Widespread blood clotting, DIC may develop later
- DHF mostly found in children under 15; can be fatal • Named after African word, means "that which bends up"
• Caused by Chikungunya virus, an alphavirus of Togaviridae family
• Transmitted by Aedes mosquitoes, especially A. aegypti and A. albopictus
• Signs, symptoms similar to dengue fever
• Fever lasts 2-5 days, followed by severe joint pain especially in extremities that can persist weeks or months
- Chronic joint problems may develop
• Occurs mainly in Africa, Asia, and Southeast Asia
• Vector now present in Brazil, Central America, the U.S.,
and many European countries; has adapted to conditions
• No specific treatment; vector control important • Ebola Hemorrhagic Fever (EHF)
• Caused by Ebola virus, named after Ebola River Valley in Democratic Republic of the Congo
• Five different species; four cause disease in humans
• Is one of two virus genera in Filoviridae family
• Causes severe, often fatal disease
• Rapid onset of fever, headache, abdominal pain, joint and muscle pain, sore throat, macular rash, and bleeding
• Virus causes capillary fragility and disrupts clotting; patients bleed from mucous membranes and body orifices; bloody vomit, diarrhea common
• Massive internal and external bleeding leads to fatality in 50-80% of cases; death is by multiorgan failure or shock
• Found in various African countries where social and economic conditions favor
• Patients kept hydrated; blood, O2 levels maintained
• Plasma containing coagulation factors given • Prevention is difficult; natural reservoir is unknown
- Suspected fruit bats carry
• Ebola virus transmitted by contact with bodily fluids
• Found in other animals including gorillas, chimpanzees; high mortality makes them unlikely reservoirs
• Quick diagnosis, rapid response essential to prevent spread; healthcare workers must be stringent in use of protective gear and infection-control measures • Ancient disease, found in early Chinese, Hindu writings
• During 4th century B.C., the Greeks noticed association with swamps, began drainage projects to control
• Italians named malaria, or "bad air" in 17th century
• In 1902, Ronald Ross received Nobel Prize for demonstrating life cycle of protozoan cause of malaria
• Most common serious infectious disease worldwide
• In 1955, WHO began program for global elimination
• Insecticides such as DDT to kill vector
• Diagnosing and treating infected patients
• Initially successful—52 nations participated
- By 1960, 10 had eradicated
• Unfortunately, mosquito vectors developed resistance
• In 1976, WHO acknowledged failure
• Today, over 300 million infected annually
- More than 1 million deaths per year
- More than when the eradication programs first began • Protozoa of genus Plasmodium, transmitted by infected female mosquito species of genus Anopheles
• P. vivax, P. falciparum, P. malariae, P. ovale, P. knowlesi
• Complex life cycle: liver stage (exoerythrocytic stage) and red blood cell stage (erythrocytic stage)
• Infectious form is called sporozoite; is carried by bloodstream to liver, infects hepatocytes
• Parasites enlarge, divide asexually, produce thousands of merozoites, which infect red blood cells (RBC)
- Some species can form hypnozoites that can live in hepatocytes for years before reproducing
• Merozoites develop into larger motile trophozoite (feeding stage) and then schizont (reproducing stage)
• Schizont divides asexually to yield merozoites when RBC ruptures; then enter new RBCs and multiply, repeat cycle
• Some that enter RBCs develop into gametocytes (specialized sexual forms), which are transmittable form
• Upon entering mosquito intestine, drop in temperature stimulates male and female gametocytes to become gametes, fertilize, form zygotes
- Zygotes form cysts that divide asexually into numerous offspring, rupture, release sporozoites, which find way to salivary glands and saliva 