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62 Cards in this Set
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- Back
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What is a vector?
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According to the WHO, it is an organism the carries the disease and transmits it, without actually becoming ill.
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What is a reservoir?
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A reservoir is a part of the life cycle of a pathogen which is where the vector picks up the pathogen.
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What is a biological vector?
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A type of vector in which the pathogen must go through a stage in its life cycle or multiply before being transmitted to human host.
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What is a mechanical vector?
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pathogen is transmitted when it is carried on a part of the vector (i.e. the leg of a fly)
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Name the 5 types of vector life cycles.
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Human-mosquito
Bird-mosquito Mammal-Mosquito Mammal-Tick Mammal-sandfly |
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Name some infections that use the mosquito human life cycle?
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Yellow fever (urban cycle)
Dengue |
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Name some infections that use the bird-mosquito life cycle?
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-Different forms of encephalitis
-West Nile Virus |
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Name some infections that use the mammal-mosquito cycle?
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Yellow fever (sylvan cycle)
Rift Valley Fever Encephalitis |
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Name some infections that use the tick-mammal cycle?
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Congo-Crimean Hemorrhagic fever
Lyme disease |
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Mammal-Sandfly cycle?
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Sandfly fever
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A middle aged man walks into your office complaining of frequent nose bleeds. He says that two days ago he developed a high fever, starting having muscle aches, and a bad headache. After examination you realize that he is also bleeding from his gums in the oral cavity and is slightly jaundiced. He also recently returned from Northern Brazil. What is the most likely clinical scenerio?
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Yellow fever (flavivirus)
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For yellow fever, common lesions on hepatic histology sections reveal necrosis' known as what?
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Councilman bodies
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Describe the Dengue Fever life cycle.
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It is a Human-Mosquito life cycle where there is no reservoir and the human is the definitive host.
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One of your world travelling patients has just returned from another epic adventure in South America. This usually upbeat individual presents in your office today complaining of muscle pain and weakness, pain behind his right eye, headaches, and a fever. He returned from Colombia 7 days ago. You notice upon examination that he has developed a rather large rash. What are you thinking might be behind this presentation?
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Dengue fever
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What are some of the clinical features of someone who has Dengue Hemorrhagic Fever?
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It usually follows a classic Dengue fever (fever, headache myalgia, rash) about 3-5 days post infection. There is a significant drop in the patients blood pressure as the peripheral perfusion on the patient weakens. It often presents with patients who are bruised, have fluid in the perioteneal or pleural space, and have severe hypotension. A positive tourniquet test is also indicative of capillary collapse. The test inflates a sphygmomanometer cuff and distal to it, you see tiny droplets of blood dot the persons skin.
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There are four criteria in diagnosing someone with DHF, name them.
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1. Fever or recent acute fever
2. Low platelet count 3. Hemorrhagic manifestations 4. Objective evidence of leaky capillaries (elevated hematocrit, low albumin) |
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What is the proper care technique in someone who has dengue fever?
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Fluids, rest, and anti-fever medication (but not NSAIDS or other cox-inhibitors, that may drop platelet counts even more)
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What are some of the clinical features associated with Arbovirus encephalitis?
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Similar pattern to other arboviruses: sudden onset of fever, myalgias, headache, progesses to neck stiffness, nausea, drowsiness, disorientation, ataxis, and coma.
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What is the pathogenesis of arbovirus encephalitis?
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It attacks vascular endothelium and neurons. PMN response causes damage to the neurons.
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How can a diagnosis be made of arbovirus encephalitis?
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CSF can be taken and observed for increased leukocytes. A definitive diagnosis must come from virus isolation or serology.
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Which virus is related to the Japanese encephalitis serogroup and a member of the Flavivirus family?
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West Nile Virus
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Describe the life cycle of West Nile virus.
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Mammals (or humans) are dead-end hosts. Normally WNV is a bird-mosquito life cycle. Infection spreads to humans only by accident. Birds are the definitive host.
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Yesterday a 10 yo boy was brought in by his worried mother because he had been running a fever for a couple days and had recently developed a rash. Upon examination you notice the rash near the ankles and the wrists. The patients spleen is also enlarged. The mother tells you that last week he had been out on a camping trip in West Virginia with his cub scout troop. What is your initial clinical diagnosis?
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Rocky Mountain Spotted Fever
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What are some of the clinical presentations of RMSF?
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The typical rash that begins on the ankles and wrists and spreads to the trunk, severe headaches, stiff neck, transient deafness, and focal neurologic defects. On histo sections mononuclear cells can be seen in the CNS.
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What is the best treatment option for RMSF?
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Tetracyclines and supportive care
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How is RMSF transmitted to humans?
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It follows the tick-human life cycle in which humans or other mammals are the definitive hosts.
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Describe the etiology and life-cycle of Typhus.
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Typhus is a member of the Rickettsia genus (as is RMSF). It's life cycle is actually a louse-human cycle. They infection begins in the site of louse bites.
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Describe the clinical signs of typhus.
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It is an infection that begins at the site of louse bites, and spreads to the vascular endothelium. People present after an incubation of around 12 days with flu-like symptoms including fever. After a few days with a fever, a typical Typhus rash develops.
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Describe the testing and treatment available for typhus.
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Testing for typhus is based on clinical presentation, recent travel to an endemic area, serology, oranism isolation.
Doxycycline works for Typhus. |
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Describe the clinical symptoms of a patient with Human Ehrlichiosis.
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Initially the symptoms are non-specific: headache, fever, muscle aches. Progression of disease may include vomiting, diarrhea, cough, and joint pain. Peripheral blood smear will often times show the organism. It will also show leukopenia, thrombocytopenia, and increases in liver enzymes.
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Treatment options for HE?
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Doxycycline is the DOC
Treatment should NOT be delayed while awaiting test results if there is clinical suspicion. |
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What is the major vector for HE?
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Hard ticks, through deer reservoirs
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What is the mechanism used by Relapsing fevers (Borrelia) to evade host immune responses?
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Variable Major Proteins
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Describe the differences between the endemic and the epidemic life cycles of the Relapsing fevers.
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In the endemic phase, the life cycle passes through soft ticks and uses rodents as a reservoir. Once a human is infected, louse are the vector for epidemic infections.
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A 45 yo man comes into your clinic complaining of a large rash on his upper rt. leg. He says he noticed it starting to form a couple days ago. You know that he is an avid hunter and he relates to you that he just went deer hunting a week ago. On examination you realize that he has a large annular rash surrounding what looks to be like a central bite location. In addition to that he complains of general ill feelings, headache, and neck stiffness. What is the clinical presentation here?
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Lyme disease, Stage 1
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Describe the three stages of Lyme disease.
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Stage 1: A bacterial infection that is a direct result of tick bite. It creates an annular rash around 3-22 days after initial bite. Patients also often complain of flu-like symptoms.
Stage 2: Occurs 1 week into symptoms. It is caused by bacterial infection and accompanying immune response. Typically effects are cardiac and neurologically related. Stage 3: Cross reactive antibodies tend to cause destruction of joint tissue. |
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There are two stages of treatment for Lyme disease...what are they?
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Stage 1: Use Doxycycline and amoxicillin
Stages 2 and 3: Use Doxycylcine and IV Ceftriaxone. |
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Describe the malaria life cycle.
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It is basically a mosquito-human life cycle, but highly complex. Mosquitos will infect humans through a bite releasing sporozoites from their saliva. These sporozoites will travel to the liver where they will invade hepatocytes. If they are P. vivax or ovale, then they will lay dormant in hepatocytes for long periods of time. For P. falciparum asexual reproduction occurs in the hepatocytes. When the cell eventually ruptures it releases merozoites into the blood. Merozoites that eventually infect RBC's are called trophozoites. These will enter a reproductive phase and called schizogony resulting in massive merozoite formation. This will eventually cause infected RBC's to lyse and release its infectious agent. Then these can infect other RBC's or grow into gametophytes which will eventually take the cycle back into mosquitos.
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Fever on a returning traveller is what until proven otherwise?
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Malaria
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Where is malaria most endemic?
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South America, Africa, and parts of South Asia
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Which type of malaria is most often seen when nephrotic syndrome is present?
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P. malariae
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Which plasmodium is most likely to cause anemia and have CNS involvement?
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P. falciparum
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What are some of the clinical signs seen in malaria?
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Typically cyclic fever and chills is noted for about 2 weeks post infection. It begins with a fever/chills followed with hot stage and sweating stage. Sometimes conjunctival hemorrhages are seen. Also non-specific: headache, ataxia, neck stiffness, convulsions. Also increased RBC adherence can cause ischemia.
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What is the membrane protein in erythrocytes that is expressed when infected by P. falciparum?
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PfEMP-1, causes endothelium binding
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Which type of blood film is used for screening for malaria?
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Thick blood film
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Which type of blood film is used for determining specific malaria species?
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Thin blood film
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What is the proper technique for diagnosing malaria through blood smears?
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It takes multiple blood smears (<3) over a 48 hour period to get an adequate diagnosis
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Which forms are most typically seen in P.falciparum infections and why?
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Normally on the ring form (trophozoite in RBC) or the gametocytes are seen because those in the Schizont phase are adhering to vascular endothelium and no longer present in circulation.
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What are the three classes of malaria medication and where do they work?
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Tissue schizonticides: work during the replicative phase in hepatocytes
Blood schizonticides: work directly on muliplying merozoites in RBC's Gametocyticides: work on the RBC's carrying gametocytes |
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List medications from each of the three classes of malaria drugs.
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Tissue schizonticides: Primaquine
Blood schizonticides: quinine, chloroquine, Mefloquine, and Artemisinin derivatives Gametocyticides: chloroquine, primaquine |
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Trypanosomiasis is seen in the Americas and Africa, what is the relation?
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Similar organism, different vectors, different diseases
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What is the African trypanosomiasis vector?
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Tse-Tse fly
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What are the four phases of african tryp infection?
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trypanosomal chancre at site of inoculation-->parasitemia-->into the blood and lymph nodes-->CNS invasion
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What is a classic sign for CNS involvment in african trypanosomiasis?
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Winterbottom's sign (enlarged cervical lymph node)
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How does the african tryp evade immune response?
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By varying its antigen type, which results in parasitemia fluctuations and antibody waves.
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How is the definitive diagnosis for African tryp made?
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Recognition of the organism on a peripheral blood smear.
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What is the drug of choice for African trypanosomiasis?
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Early infxn: Suramin
CNS involvement: Melarsoprol |
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What is the vector for American trypanosomiasis?
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Reduviid bug
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What is the drug of choice for American tryp?
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Nifurtimox or benzimidazole
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An ulcer in a returning traveller is what until proven otherwise?
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Leishmaniasis
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What is the main vector in Leishmaniasis?
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Sandfly, with reservoirs in rodents and canids?
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For visceral leish, what is the clinical presentation?
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Amastigotes are seen in the reticuloendothelial system (phagocytic cells residing in reticular tissue [Kupfer])
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