Microbiology Homework
1. Compare and contrast Gardnerella vaginalis and Trichomonas vaginalis. How do you tell the two apart? Both organisms cause vaginosis in females and are asymptomatic or cause urethritis in males. The vagnial discharge is considered foul smelling in both cases, though Gardnerella is diagnosed by treating the discharge with KOH which increases the odor, which is said to have a fishy or musty smell. The color of the discharge is yellow-gray for Gardnerella and yellow-green for Trichomonas. To definitively tell the two apart one needs to observe samples of vaginal secretions and fresh urine under a microscope. Gardnerella shows few white blood cells and lactobacilli. The characteristic "clue cells" are identified as numerous stippled or granulated epithelial cells. This appearance is caused by adherence of almost uniformly spaced G vaginalis organisms on their surfaces. Clumps of G vaginalis organisms may also be noted attached to the edges of epithelial cells or floating free in the preparation. Cultures are seldom necessary to establish a diagnosis. Trichomonas vaginalis multiplication is triggered by a pH shift in the vagina associated with the menstrual cycle, and the trophozoite has 5 polar flagellae. Trichomonas differs from Garnerella in that the discharge is frothy, and it causes discomfort with sex, itching. The organism can be visualized in a wet mount of fresh urine: look for swimmers with 5 flagellae. They are hard to ID when they're not moving.
2. Compare and contrast Taenia solium and Ascaris lumbricoides. Draw pictures of infectious particle for each parasite.
T. soleum
--pork tapeworm causing cysticercosis
--Morph: adult worm is ~4 meters in length, branched uterus, four suckers on scolex ("head") and two rows of hooks
--Dx: unembryonated eggs in feces and antibodies for cysticercosis
--infects pigs, humans
--distrib: Asia, Africa, the Philippines, South America, parts of S. Europe & N. America
--cyclophyllid cestode
--humans are host
--Trans: eating infected meat, fostering adult tapeworms in the intestine, and passing eggs through feces, can be passed by vomiting
--S/Sx: cysticerci often in CNS can cause major neurological problems like hydrocephalus, cerebral edema, cerebral compression, or epileptic seizures and death
--Dx: difficult to diagnose in its early stage and may be apparent only when the first neurological symptoms start, or when a CT scan, or an MRI of the brain is performed for other reasons. Antibody tests or a biopsy of the affected area may be necessary to complete the diagnosis.
--Dx: eggs only tell you the family of the worm
--Dx: MRI of brain, seizures, and headaches are common symptoms, also: confusion, lack of attention to people and surroundings, difficulty with balance, hydrocephalus (compression of the brain tissue due to obstruction of cerebrospinal fluid flow) may also occur
--Dx: stain proglottid's uterus with India ink, 5-10 branches on uterus indicates solius
--Dx: In muscles, cysts cause painless swelling or create nodules under the skin
--Dx: cysts in the eye impair vision by floating in the eye and can cause blindness (detachment of the retina)
--Dx: heart lesions can lead to abnormal rhythms or heart failure (rare)
--Dx: often few symptoms until the parasite dies: immune response to dead worm causes swelling, scarring and symptoms
--Dx: Spinal cord lesions can lead to partial loss of motor control, weakness, and even paralysis.
--Prevent: proper disposal of human feces around pigs, cook meat thoroughly, freeze meat 5 days @ -10oC
--Tx: niclosamide, suppress vomiting
--Tx: Praziquantel and Albendazole for neuro, Steroid anti-inflammatories
--Tx: killing worm can cause onset of siezures
--Tx: if cysticerci have calcified in the brain, or if there is only one lesion, treatment is not considered beneficial.
A. lumbricoides
--round worm
--global, rural, common in kids 5-9 years of age
--Morph: adult worm 15-35 cm, female is larger
--Trans: fecal/oral
--S/Sx: vague abdominal pain, breif cough, wheeze, substernal discomfort
--Dx: eggs in stool
--Tx: mebendazole
--Morph: egg of this nematode has a thick shell wall resistant to the external environment
--embryonated eggs containing the L1 larval worms may also be seen, as on the right here.
--Infection common, over 1500 million cases, or around one quarter of the worlds population
--Ascaris lumbricoides is morphologically indistinguishable from Ascaris suum found in the PIG.
--MORPH: adult Ascaris lumbricoides are large white, or pinkish-white, cylindrical roundworms, slightly narrower at the head, with a smooth, finely striated, cuticle, and a mouth with three lips each equipped with small papillae
--eggs are highly characteristic: shell has thick transparent inner shell covered in warty albuminous coat
--adult parasite lives in small intestine of man, feeding on the semi-digested contents
--can bite the intestinal mucous membrane and feed on blood and tissue fluids
--female parasite is highly prolific, laying an estimated 2 million eggs daily
--differentiation occurring outside the host
--eggs are infective and mature in approx 3 weeks
--eggs may remain viable in the soil for many years if conditions are optima
--Trans: Infection occurs on ingestion of raw food, such as fruit or vegetables, that a contaminated with these infective eggs. The eggs then hatch in the small intestine, to release the rhabditiform larvae (measuring approximately 250 by 15µm in size. These do not simply grow into the adult forms in the intestine, but must then undergo a migration: they penetrate the intestinal wall, entering the portal blood stream to the liver, then heart, then after between 1 to 7 days, the lungs. Here they moult twice on the way to form the L4 larvae, (measuring approximately 1.5mm long), then burrow out of the blood vessels, entering the bronchioles. From here they migrate up through the air passages of the lungs, to the trachea. They then enter the throat and are swallowed, finally ending up in the small intestine where they mature and mate, to complete their lifecycle.
PATHOLOGY: (depends on parasite burden)
--intestinal blockage
--adult parasites often leave the small intestine to enter other organs--> various pathology
--in bile duct -->blockage causing jaundice and interference in fat metabolism
--in appendix or through the intestinal wall--> fatal peritonitis
--migrate up through the intestinal tract, to be either vomited up or emerging through the nose
--in trachea-->suffocation
S/Sx:
--most infx are asymptomatic (approx 85%), or "failure to thrive"
--migrating larvae, particularly in lungs-->haemorrhagic pneumonia
--breathing difficulties, pneumonia and/or fever
--many of the parasites proteins are highly allergenic
--migrating larvae in lungs often associated with allergic hypersensitivity rxns: asthma, pulmonary infiltration and urticaria and oedema of the lips.
--malnutrition
--due to the adult parasite--> generalised digestive disorders, vague abdominal discomfort, nausea, colic.
3. Toxoplasma gondii. Obligate intracellular protozoan. How can a pregnant woman avoid infection? Don't get a new cat, don't change the kitty litter, don't eat raw or undercooked meat, wash your cutting boards and knives to avoid accidental exposure to uncooked meat, wash veggies well. Get a TORCH panel done early in pregnancy or before getting pregnant. What are the major complications of infection of a pregnant woman? 5-10% miscarry, 8-10% show serious brain and eye damage to fetus, 58-70% give birth to normal offspring who may later develop reino-chorditis or mental retardation. Fetus may also develop hydrocephalus. How do you know if an unborn child is infected? Blood serologic test on the mother, first, to see if there is any risk. Also attempt to isolate organism from tonsil or lymph of mother. Important to assess the time of infection. Only the mother's first infection is dangerous to fetus. There is no noninvasive way to know if the child is infected.
4. Hunter question: is the bite a bedbug or a tick? Hunter has circular rash on his arm, 3" in diameter and acquired while hunting for a weekend and staying in a cabin in the NE where Lyme disease is present. Circular rash is almost certainly NOT from bed bugs. Bed bugs cause small, hard, swollen white raised welts that itch. They tend to occur in tracks, not in circles. Also bed bugs would leave specks or blood stains on sheets and have a sweet odor. They would cause no more symptoms after the initial itchy bites unless there is an allergic reaction, which would be apparent soon. A tick bite, on the other hand, from an Ixodes tick, can cause Lyme disease which has many stages and possible outcomes, and is difficult to treat. Lyme disease infection is marked by a petechial "bullseye rash" which is what the hunter sounds like he has. The infectious organism is Borrelia burgdorferei, and in addition to the rash the hunter may experience early flu like symptoms. Later Borrelia can cause disseminated disease that involves the heart and nervous system, and causes palsies and meningitis. Later on the bacterium can cause motor and sensory nerve damage, brain inflammation and arthritis. Early diagnosis and treatment is essential, because it is very difficult to treat once disseminated.
5. Compare and contrast mode of transmission and major symptoms of Loa Loa vs Wuchereria bancroftii. Loa loa eye worm is acquired from a deer fly bite in an African equatorial rain forest, specifically in swampy areas of the forest, principally in the Congo River region, Sudan, and Ethiopia. Diagnosis is by detection of the microfilariae in the blood. Four to seven days after the bite there may be subcutaneous swelling, redness and angioedema in the extremities. The rest of the symptoms may not appear for months or years after the bite of the fly. The worms migrate through the skin causing local inflammatory reactions called Calabar swellings. The worms can often be seen migrating across the conjunctiva and cornea of the eye. The worm sometimes enters the brain causing encephalitis.
Wucheria bancroftii on the other hand is also a worm, and also tropical, but it is transmitted by the mosquito. Signs and symptoms include swollen lymph notes and a recurrent high fever that can keep coming back for 8-10 weeks, occurring for 3-7 days each time. Untreated it may cause elephantitis, splenomegaly, and will certainly result in eosinophilia. Diagnosis is by detection of the microfilariae in the blood, same as Loa loa. Lymphatic filariasis symptoms predominantly result from the presence of adult worms residing in the lymphatics. Additional symptoms include testicular pain, inguinal pain, or both; skin exfoliation and limb or genital swelling. People with microfilaremia are generally considered to be asymptomatic, although those with heavy microfilarial loads may develop acute and chronic inflammatory granulomas secondary to splenic destruction. Passage of cloudy milklike urine may denote chyluria. Tropical pulmonary eosinophilia (TPE): TPE is a form of occult bancroftian filariasis. Presenting symptoms include a paroxysmal dry cough, wheezing, dyspnea, anorexia, malaise, and weight loss.
6. Cisticercosis is the most common parasitic infestation of the CNS worldwidw. What is the infecting organism and how is it acquired? Taenia solius is acquired by eating undercooked pork. Diagnosis is difficult in its early stage and may be apparent only when the first neurological symptoms start, or when a CT scan, or an MRI of the brain is performed for other reasons. Antibody tests or a biopsy of the affected area may be necessary to complete the diagnosis. One might also look for unembryonated eggs in feces, though they only tell you the family of the worm and not the species. Also for diagnosis look for antibodies for cysticercosis, or a history of eating possibly infected undercooked meat. Cysticerci prefer to inhabit the CNS causing major neurological problems like hydrocephalus, cerebral edema, cerebral compression, or epileptic seizures and death. Prior to these advanced signs you may find headaches, confusion, lack of attention to people and surroundings, difficulty with balance, or hydrocephalus. In muscles, cysts cause painless swelling or create nodules under the skin. Cysts in the eye impair vision by floating in the eye and can cause blindness (detachment of the retina). Heart lesions can lead to abnormal rhythms or heart failure (rare). There are often few symptoms until the parasite dies: immune response to dead worm causes swelling, scarring and symptoms. Spinal cord lesions can lead to partial loss of motor control, weakness, and even paralysis. Treatment can be dangerous because killing the worm can cause onset of siezures. If cysticerci have calcified in the brain, or if there is only one lesion, treatment is not considered beneficial.