9 The host-parasite relationship Flashcards

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1
Q

Metagenomics is study of host microbiome. Which includes host flora and genetic material. Microbiome is a consequence of different body areas which hare exposed to external environment.

Studied through DNA sequencing, and comparing to known databses.

When is microbiome acquired?

What factors influence this?

A

Rapidly during/ after birth

Age
Nutrition - e.g breast/ bottle fed
Environment
Immunodeficiency

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2
Q

Skin - exposed dry areas are not good for bacteria growth.

Moist areas (axillae/ scalp, toes/ perineum) support larger populations.

What are common skin commensals?

A

Staph epidermidis

Staph aureus

Anaerobic diptherioids - proprionibacterium acnes. Live in hair follices/ sebaceous glands. Diptherioids are all corynnebacterium which are usually non-pathogenic

Candida

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3
Q

What are common commensals in mouth/ teeth and nose?

A

Majority are anaerobes

Strep pyogenes
Strep mutans - dental caries
Staph
Diptherioids
Gram neg cocci - neisseria meningiditis

Staph/strep/ neisseria potentially pathogenic

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4
Q

What are common commensals in pharynx/ trachea

Respiratory tract normally quite sterile despite large intake of organisms by breathing

A
Streptococci
Staphylocci
Anaerobes
Neisseria
Diptherioids

PCP if immunocompromised

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5
Q

Stomach acid normally kills most bacteria

What bacteria can live in the stomach

A

Helicobacter pylori

Streptococci

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6
Q

What are common commensals in small and large intesitne

A

Streptococci
Lactobacilli
Bacterioides
Clostridium

E. Coli
enterobacteriaceae

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7
Q

What are common commensals of urethral tract

What are common commensals of vagina

A

Usually lightly colonoised

Staoh epidermidis
Strep faecalis
Diptherioids

Vagina before puberty - as above
After puberty - lactobacilli predominate, fermenting glycogen for maintenance of acid pH, preventing overgrowth of other organisms. Candida can overgrow. Trichomonas vaginalis can be present in healthy individuals

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8
Q

How are microbiota beneficial to host/ preventing other pathogens growing?

A

Skin bacteria produce fatty acids, prevent other species growing

Gut bacteria release bacteriocins/ colicins which prevent other species growing

Vaginal lactobacilli maintian acid environment which prevent other species gorwing

Sheer number of bacteria present in intestine prevent other species growing

Evidence gut bacteria produce B vitamins, and vitamin K, which are valuable if diet is deficient.

Antigenic stimulation provided by intestinal flora helps ensure normal development of immune system

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9
Q

Disease is not inevtiable outcome between microrganisms and humans

What are three broad species of symbiosis?

Microbes can change their relationship depending on changing factors , and can become harmful. e.g Bacteriodes, E. coli staph aureus

A

Commensalism - shelter and food. Bacterioides ferment digested food, but does not cause harm

Mutualism - reciprocal benefit. Bacterioides in rumen of cattle - metabolise host food to fatty acid and gas. Fatty acids used by host

Parasitism - unilateral benefit. Entamoeba histolytica feeds on gut mucosa causing ulcers and dysentery. All pathogens are parasites. Parasitism not limited to protozoa/ worms

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10
Q

Many organisms are parasitic. Evolution has conferred this benefit, as parasite can focus on replication, as resources are provided by host.

Viruses are completely dependent on host for all metabolic needs - obligate parasites

Why do some parasites have very specific hosts?

What are disadvantages of parasitism?

A

Specific binding proteins
Some parasites have complex regulatory pathways, and requiring signalling while in host. If cycle in host is complex, host can regulate/ slow replication

Parasites may die outside of host. Several have mechanisms to survive - virus particles, bacterial spores, protozoan cysts, worm eggs

Host may control replication - so not in control of replication cycle.

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11
Q

Below are examples of evasion strategies by parasites. The most successful parasites are ones which can cope with or evade the host’s response. Give examples of microbes which use these strategies

Elicit minimal immune response

Evade effects of response

A

Elicit minimal immune response - HSV has long latent period

Evade effects of response - Mycobacterium survive unharmed in granulomas

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12
Q

Social and behavioural changes effects infectious diseases.

What are the results of changes below:

Altered environment e.g air conditioning

Changes in food production and food handling

Routine use of antibiotics

Routine use of immunosuppressive therapy

A

Altered environment e.g air conditioning - legionella

Changes in food production and food handling - drug resistant bacteria. Inadequate cooking allows listeria/ salmonella to enter body

Routine use of antibiotics - MRSA

Routine use of immunosuppressive therapy - opportunistic infections - pseudomonas, candida, pneumocystis

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13
Q

Social and behavioural changes effect infectious diseases

What are the results of changes below:

Altered sexual habits

Breakdown of filtration systems, overuse of limited water supplies

A

Altered sexual habits - gonorrhoea, genital herpes, AIDS

Breakdown of filtration systems, overuse of limited water supplies - transmission of animal infection leading to diarrhoeal disease - cryptosporidioisis, giardiasis, leptospirosis

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14
Q

Social and behavioural changes effect infectious diseases

What are the results of changes below:

Increase in ownership of pets

Increased frequency of journeys to tropical and subtropical countries

A

Increase in ownership of pets - toxoplasma, toxocara, chlamydia, salmonella

Increased frequency of journeys to tropical and subtropical countries - exposure to vectors malaria

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15
Q

Below are examples of evasion strategies by parasites. The most successful parasites are ones which can cope with or evade the host’s response. Give examples of microbes which use these strategies

Depresss host’s response

Antigenic change

A

Depresss host’s response - HIV destrys T cells, malaria decreases immune response

Antigenic change - viruses, spirochaetes, trypanosomes - change antigens so host responnse is ineffective

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16
Q

Below are examples of evasion strategies by parasites. The most successful parasites are ones which can cope with or evade the host’s response. Give examples of microbes which use these strategies

Rapid replication

Survival in weakly responsive individuals

A

Rapid replication - viruses, bacteria, protozoa - producing acute infections before recovery and immunity

Survival in weakly responsive individuals - genetic heterogeneity in host populations means some hosts wont be able to provide immune response

17
Q

What are Strep pyogenes (GAS) sequale?

A

Rheumatic fever
glomerulonephritis

Cell wall has M proteins - over 150 exist

M1/ M3 associated rheumatic fever

M12/ M49 associated with glomerulonephritis

During primary infection, antibodies develop against M proteins. These cross-react with with basement membrane of glomerulus, or myocardium

18
Q

55 year old suffered abdominal trauma/ splenectomy 10 years ago, presents with fever, cough, SOB. Diagnosed CAP. Third infection this year

What is most likely organism?

S pneumoniae
H Influenzae
S aureus
K pneumoniae
Pseudomonas
A

H influenzae

Splenectomy increases risk of streptococci, haemophilus, neisseria meningitidis

Spleen normally removes circulating bacteria through phagocytic filter mechanism, and producing antibodies when splenic B cells become activated

Most other methods of removing bacteria require opsonisation. Bacteria that have capsules are not well opsonised, as capsules prevent antibody attachment to bacterial cell wall. However, spleen is good at removing these normally

19
Q

28 year odl IVDU present severe diplopia. Then develops difficulty swallowing, slurred speech, and descening symmetrical weakness.

What is next stage of management?

A

IV botulinum anti-toxin

Surgical debridement of any abscesses. Can release more toxin, so should be performed following anti-toxin administration

IV benzylpenicillin

Botulinum toxin A-G exist, but human disease usually caused by A, B, E. Binds to receptors in presynaptic membrane of neuromuscular junction, resulting in muscle weakness.