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29 Cards in this Set
- Front
- Back
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Gastrointestinal waterborne - Cholera
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- caused by vibrio cholera bacterium (gram -ve, comma shapes)
- needs very high infective dose (10^8/9), more common in those with weakened immune systems due to malnutrition etc - disrupts ions in the cells and causes extreme dehydration and death (if untreated) |
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Gastrointestinal waterborne - Typhoid fever
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- caused by salmonella typhi bacterium
- person to person transmition from sewage in water - not typical symptoms, more flu like eg fever, distinct rash, abdominal pain etc |
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Gastrointestinal waterborne - Norwalk virus
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- humans the only host
- comes from shell fish or contaminated water, person to person transmission, common in the uk - causes diarrhoea, vomiting, stomach cramps, lasts 2-3 days |
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Gastrointestinal waterborne - Cytptosporidium parvum
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- parasitic protozoan, highly infectious
- transmitted via contaminates water or person-person, increases after rainfall (from cattle faeces so oocysts wash into water supplies) - oocysts v.small so cant be filtered out and unaffected by disinfectants - causes weight loss, pain, diarrhoea but is self limiting (immune system easily overcomes) |
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Respiratory waterborne - Legionnaires disease
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- caused by legionella pneumophila, when inhaled in water droplets in the ear
- spread by shower heads/air con etc - high mortality (esp in elderly) can survive in cells within the immune system |
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Skin waterborne - Leptospirosis
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- caused by leptospidium interrogans from animal (rodent) excretions
- enters through breaks in skin and causes flu like symptoms - 90% of causes resolved but when complications arise causes jaundice, hepatitis, kidney damage, blood clotting, meningitis |
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Skin waterborne - Sehistosoma sp
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- blood flukes (multicellular parasite) which cause schistosomiasis
- eggs have hooks which allow them to enter vector (water snail), larvae than form and can penetrate human skin - causes inflammation in liver, kidneys etc |
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Foodborne - Causes
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- Chemical: intrinsic natural toxins (legume or algal toxins) or extrinsic contamination (pesticides)
- Infectious disease agents (bacteria, fungi, protozoa, virus etc) |
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Foodborne - Factors affecting microbial growth in food
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- Nutrients availability: food generally are a good source of nutrients (can be used in growth cultures in the lab) so can easily grow on food stuff.
- Antimicrobial barriers/agents: skin (non permeable) and chemicals (such as allicin in garlic) can prevent microbe growth in food stuff. - food like meat and seafood more susceptible from filter feeding in molluscs and CO2 and low humidity in abattoirs. |
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Foodborne - Defences against foodborne infection
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- Intestinal tract: acid, proteoltic enzymes, bile salt, rapid flow of material, rapid cell turnover, microflora in the colon
- infective dose: varies largely, some easy to avoid as need many bacteria others like Ecoli only need 10 cells to infect |
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Foodborne bacterial causes - Campylobacter jejuni
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- poorly understood pathogenesis (seems to produce cholera like toxins)
- flagella adhere to intestinal mucosa causing local tissue damage which produces inflammation and bleeding - favours microaerophilic conditions |
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Foodborne bacterial causes - Salmonella species
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- flagella (increase SA) adhere to intestinal mucosa and invade cells in small intestines, stimulating an immune response as microbial load increases which can produce pain
- can spread and cause vomiting which is a sing of secondary infection and can be fatal - gram negative, non-spore producing rods, facultative anaerobes, |
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Foodborne bacterial causes - Bacillus cereus
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- not much data as short lived infection, only lasts 24hrs, from rice and veg, two different forms of enterotoxin which either cause vomiting or diarrhoea
- gram positive, aerobic spore forming rods, can be heat liable or heat stable (hence to pathways of symptoms) |
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Foodborne bacterial causes - Enterohaemhorragic E.coli
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- attach to mucosa, produce toxin, causing severe diarrhoea results, other symptoms including vomiting haemorrhagic colitis also occurs
- complications include HUS (haemolytic uraemic syndrome) where toxins destruct red blood cells and causes kidney failure due to immune response |
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Foodborne bacterial causes - Listeria monocytogenes
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- causes listeriosis, found in soft cheese, vacuum packages meat and unwashed veg
- gram positive, aerobic rods which can survive at low temps (4c) - can cross the placenta causing severe disease such as abortion, septicaemia and meningitis |
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Foodborne other causes - Taenia spp
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- tape worm
- can treat by dissolving or paralysing tapeworm depending on the type of worm |
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Foodborne other causes
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- viruses: hep A, norwalk, rotavirus
- fungi: claviceps purpurea, aspergillus flavus - prions - helminths |
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Airborne transmission
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- via droplets expelled during speech, coughing, sneezing etc
- can be direct person-to-person contact or indirect via a vehicle such as door handle - some micro-organisms are short lived in droplets whilst others can withstand drying out |
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Airborne bacterial causes - Mycobacterium tuberculosis
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- can be either pulmonary TB (common in uk) or extrapulmonary which affects the lymph system, kidneys, bones etc
- risk factors: over crowding, close contact with infected person, weakened immune system (AIDS), visiting a tb prone country, chronic health problems though lifestyle (homelessness, drug abuse, alcoholism) the very young or very old. - infection pathway: 1) can resolve on its own 2) active tb causes primary symptoms (coughing, fever, weight loss, swollen glands) 3) asymptomatic tb during a latent/dormant phase were bacterium survive within macrophages and again resistance, reactivated when immune system is weakened - diagnosis: xrays and skin tests (heaf or mantoux) - treatment: BCG vaccine and long course of mixed antibiotics |
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Airborne bacterial causes -Staphylococcus areus
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- carried on skin without disease, resistant to drying so carried in dust particles and transmitted via direct or indirect contact.
- causes many diseases eg impetigo, osteolmyelitis, boils and toxic shock syndrome (TSS, causes high fever, vomiting, rash, red eye, dizziness, can be fatal via kidney/liver damage) - treatment: mulitple antibiotics (resistant strains prominent eg MRSA) |
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Airborne viral causes - Cold/flu
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- COMMON COLD: caused by many viruses eg rhinovirus, adenovirus and caronovirus
- FLU: caused by influenza A, B or C and has more acute symptoms such as high fever, vomiting/diarrhoea, headache, tiredness. Eg Influenza A is an avian flu made from a single stranded RNA genome in 8 segments enclosed by a lipoprotein capsule which antigentically distinct protruding haemoglutinin's and neurominidase's (gives the name H1N1 etc created via reassortment or intoto mutations). replicates inside the hosts cells using their raw materials and mechanisms destroying them by lysis. |
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Zoonoses/vector borne - Yersina pestis
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- gram negative, facultatively anaerobic rod shaped bacteria that causes the plague
- 3 pandemics (plague of justinian, the black death, plague of china) currently still 1000-2000 cases/yr -Infection cycle: SYLVATIC PLAGUE is the nonfatal cycle present in wild rodents, bacterium transmitted via fleas between animals. URBAN PLAGUE occurs in urban rodents when the flea find human hosts in overcrowded, insanitary condition due to strain becoming fatal in urban unresistant host and flea moving onto human hosts. - PATHOGENESIS: bubonic plague (bacteria killed at infection site by neutrophiles but taken up by macrpphages and multiply, when macrophage is killed bacterium released (no have resistant virulence characteristics) and spread through lymph system to lymph nodes where they multiply further and cause greater loss of macrophages, nodes become swollen and hemorrhagic (black buboes)) Pneumonic plague (bacteria move into the blood (bacteraemia) and release endotoxin which results in systematic shock, liver damage, respiratory distress due to the infection of organs (esp lungs) where it can now be transmitted via droplet infection to other humans - treatment: antibiotics such as streptomycin + tetracycline, fatal if not discovered early. |
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Zoonoses/vector borne - Plasmodium variants
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- P.flaciparum, P.vivax, P.ovale and P.malariae all cause malaria (neck stiffness, abnormal breathing, fever) transmitted via mosquitos
- Life cycle: sporozoites in the mosquitos salivary glands are injected into the hosts blood and travel to the liver and enter the parenchymal cells, EXOERYTHROCYTIC STAGE (parasite replicates and enlarges to schizont, which divides into smaller merozoite cells which rupture liver cells and enter blood stream) ERTHROCYTIC STAGE (merozoites invade erythrocytes where they replicate , exit and reinfect further cells, results in fever. merozoites differentiate into male/female and carried in blood as gametocytes to feeding mosquito where they mature and fertilise to for zygote which develop into motile ookinete), SPOROGONIC CYCLE (ookinete penetrates mid gut wall and develops into an oocyst which grows, ruptures and releases sporozoites which migrate to the salivary glands (maturation)) - treatment: quinine kills sporozoites, chloroquine acts within red blood cells, primaquine acts outside red blood cells. Resistance is present, try to control with pesticides, removal of habitat, nets, repellents etc |
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Zoonoses/vector borne - Rickettisia species
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- small, gram negative, obligate intracellular bacteria.
- replicate at site of bite leading to necrosis of tissue, spread systematically and invades endothelial cells causing haemorrhaging (rash) and fever, headache. - TYPHUS GROUP: epidemic typhus caused by R.prowazekii, spread by louse to humans (serious). Murine typhus caused by R.typhi spread by fleas to rodents (less serious) - SPOTTED FEVER GROUP: rocky mountain sf caused by R.rickettsii, spread by ticks to rodents/dogs (serious), african tick typhus caused by R.conorii, spread by ticks to dogs/rodents (less serious) - treatment: tetracycline/dexoycycline |
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Zoonoses/vector borne - Rhabdovirus
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- causes rabies via transmission of virus laden saliva by bite/scratch
- Pathogenesis: multiplies in bite wound in surrounding muscle/connective tissue, enters peripheral nervous system via nicotinic acetylcholine receptors on nerve surface, spreading up CNS where it proliferates and causes encephalitis - symptoms: nonspecifc (malaise, nausae, sore throat), neurological (pupil dilation, excessive salivation, anxiety, muscle spasms, fear of swallowing), final stage is convolsions followed by coma, respiratory paralysis and death. - Treatment: pre/post vacine available with attenuated virus to raise immune response. |
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STD's - Neisseria gonorrhoeae
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- causes gonorrhoea, is a very sensitive bacteria, can be transmitted to infant during birth
- symptoms: MALE (painful urethra, prostatitis, epididymitis), FEMALE (mild vaginitis, can be symptomatic, salpingititis, pelvic inflammatory disease) can become disseminated if immuno depressed and cause septicaemia. - pathogenesis: pili attach to epithelium cells, taken into cells causing inflammation, replicates on basement membrane, transcytosed out of cell and phagocytosed, surviving bacteria released as pus. -diagnosis: intracellulr gram negative diplococci, grow on selective media or viewed directly from smears. - treatment: resistant to penecillin so use ceftriaxone. |
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STD's - Chlamydiae
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- complex bacterium with two stage growth, that causes chlamydia.
- symptoms: MALE (non-gonococcal urethritis, mucoid discharge, post-gonococcal urethritis) FEMALE (mucopurulent cervicitis, urethritis, pelvic inflammatory disease) - pathogenesis: bacterium ingested into cell and becomes phagosome, becomes metabolically active, replicated, condenses and released. - diagnosis: growth in culture (difficult as very sensitive), immunofluorescence (sensitive but difficult for large numbers), immunoassays (can use large sample but lower specificity), PCR (sensitive and specific, can use large sample, high cost) - treatment: course of tetracycline or doxycycline |
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STD's - Treponema pallidum
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- gram negative bacterium causes syphilis via broken skin.
- symptoms: primary (painless ulcer/chancre), secondary (systematic illness, fever, tiredness, malaise), latent (symptomatic), tertiary (neurological/cardiac symptoms) - diagnosis: cant be grown in culture (obligate human pathogen), spirochetes can be seen in primary lesion using microscopy - treatment: penicillin |
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STD's - haemophilus ducreyi
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- gram negative bacteria causes chancroid, mainly in tropics
- symptoms: painful ulcer.chancre, often associated with HIV - diagnosis: culture on media is very difficult, use PCR if available or elimination of syphilis using microscopy - treatment: resistance present but still treatable with erythromycin and ciprofloxacin |
