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BS1040: Microbiology and Cell Biology > MC3-4: Eukaryotic microbial pathogens > Flashcards

MC3-4: Eukaryotic microbial pathogens Flashcards

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1
Q

Define ‘facultative parasite’

A

An organism that lives and can complete its lifecycle independent of a host, but may occasionally be parasitic under certain conditions, e.g. when immunocompromised

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2
Q

Define ‘obigate parasite’

A

A parasite that cannot lead an independent, non-parasitic existence

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3
Q

Define ‘opportunistic parasite’

A

A parasite that takes advantage of certain opportunities to cause disease. Many lie dormant in the host until the immune system is reduced

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4
Q

What are the three ways in which a fungus can infect a human? Which are the most common?

A
  • Superficially (on the skin) – more common
  • Subcutaneously (under the skin) – less common
  • Systemically (multi-organ) – more common
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5
Q

What are dermatophytes?

How are dermatophyte infections acquired by humans?

Name two examples of dermatophyte infections.

A

Dermatophytes are moulds that grow on keratin (e.g. on the skin)

Infection is acquired from people, animals, or the environment, depending on the species

Examples of diseases: athlete’s foot, ringworm

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6
Q

Why do dermatophyte infections cause a circular wound?

A

They eat the keratin and then move outwards when they run out

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7
Q

What is candidiasis and what causes it?

A

Oral or vaginal thrush

Opportunistic Candida albicans following antibiotics and T-lymphocyte deficiencies

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8
Q

Define ‘commensalism’

A

A relationship between two organisms where one organism benefits from the other without affecting it

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9
Q

Define ‘polymorphic’ and give an example of a polymorphic fungus.

A

An organism that can grow as both a yeast and as filamentous cells

e.g. Candida albicans

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10
Q

What percentage of humans are infected with Candida and where are the most common sites of infection?

A

80%

Intestine, colon, mouth

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11
Q

What percentage of women have had candidiasis and what is the most common cause?

A

75%

Following antibiotic treatments

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12
Q

How can Candida albicans be pathogenic if they are commensal?

A

If the host has low immunity or if there is a change in natural microbiota of physiology

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13
Q

How does Candida albicans cause disease?

A

It attacks the skin or mucosae and invades tissue by puncturing skin with its hyphae

If nutrient-rich environment, spores are produced and the population doubles in an hour

Biofilms can grow on implantable medical devices

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14
Q

What is Cryptococcus neoformans, what does it cause, and how is it acquired?

A

A yeast, causing chronic meningitis

Probably acquired from the environment, possibly pigeon droppings

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15
Q

How does Pneumocystic carinii grow, what does it cause, and what is the route of infection?

A

Grows intracellularly

Produces serious pneumonia in immunocompromised

Route of infection uncertain, but endogenous and exogenous routes likely

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16
Q

Define ‘endogenous’

A

When an organism already carries a pathogen

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17
Q

Define ‘exogenous’

A

When an organism does not already carry a pathogen and acquires it from outside

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18
Q

What are Aspergillus and what do they cause?

A

Ubiquitous mould

Causing pulmonary and systemic infections, e.g. allergic aspergillosis (triggering asthma and COPD)

Can cause aflotoxin (a neurotoxin) and aspergilloma (lumps)

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19
Q

Why are effective antifungal drugs hard to find?

A

Many drugs do not differentiate between fungi and humans

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20
Q

What are the three ways in which antifungal drugs work? Give examples of each type.

A
  • Cell wall integrity, e.g. nystatin, amphotericin B
  • Cell wall biosynthesis, e.g. fluconazole, itraconazole, miconazole, terbinafine
  • RNA synthesis: flucytosine (5-fluorocytosine)
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21
Q

What diseases can protoxoal pathogens cause in humans?

A
  • Malaria
  • Toxoplasma
  • Intestinal and vaginal infections
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22
Q

Where are Naegleria found?

A

In warm fresh water, such as cooling towers in nuclear power stations

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23
Q

How does Naegleria affect humans?

A

Infects humans through their olfactory nerve (through the nose)

Ultimately causes a fatal brain disease
(primary amoebic meningoencephalitis or PAM/PAME)

Known as the brain-eating amoeba

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24
Q

What is the life cycle of Naegleria?

A
  • Flagellate stage:
    • A small pear-shaped organism with two flagellae
    • Mobile
    • Stage that infects people who are exposed through water
  • Amoeba form:
    • ​Occurs after infection
  • Cyst stage:
    • ​Occurs in response to unfavourable environmental conditions
    • Resistant to harsh environmental conditions
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25
Q

Where are Naegleria fowleri usually found?

A

In warm-water environments

26
Q

What is one of the most common amoebae found in soil, fresh water, and the natural environment?

A

Acanthamoeba

27
Q

How big are Acanthamoeba?

A

15-35μm

28
Q

Where are Acanthamoeba found?

A

In fresh water (e.g. contact lens solution) and salt water

29
Q

How do Acanthamoeba affect humans?

A
  • They infect humans through contaminating contact lenses/contact lens cases
  • Can also infect broken skin and cause cutaneous disease or even spread to the brain via the blood
  • Can also infect the mucosa and then the brain in a similar way to Naegleria
30
Q

What is the life cycle of Acanthamoeba?

A
  1. Cysts
  2. Trophozoite (infective)
  3. Amoebae which can enter humans in many ways
31
Q

What diseases can Acanthamoeba cause?

A
  • Acanthamoeba keratitis (AK) – eye disease
  • Cutaneous amoebiasis – skin disease
  • Granulomatous amoebic ancephalitis (GAE) – brain disease
32
Q

What is acanthamoeba keratitis (AK)?

A
  • Progressive sight-threatening corneal disease
  • Leading risk factor is contact lens water
  • Most common type of Acanthamoeba infection
  • Treatment is not always successful and corneal transplants often required
  • Reactivation occurs if in transplanted cornea
33
Q

What are coccidia?

A

Obligate intracellular parasites that infect the intestinal tracts of mammals

34
Q

What are common characteristics of coccidia?

A

Sexual cycle occurs in epithelial cells (gut in most species)

Oocysts (infective stages) secretion after sexual cycle. Environmentally resistant

35
Q

Define ‘trophozoite’

A

The feeding stage of a protozoan parasite

36
Q

Define ‘schizogony’

A

The process of asexual reproduction during which the nucleus undergoes division preceding cell division

37
Q

What are ‘merozoites’?

A

The daughter cells produced by schizogony. They can develop into gametocytes or enter new host cells and undergo another cycle of schizogony

38
Q

Define ‘gameocyte’

A

Cells that are capable of developing into gamete. They are derviced from merozoites

39
Q

Cryptosporidium were once thought to have many species. What is the current view?

A

They contain only a few species that have broad host specificity

40
Q

What is the lifecycle of Cryptosporidium?

A

Direct faecal-oral life cycle with no intermediate hosts

41
Q

Why did diseases caused by Cryptosporidium come to light in the 1980s?

A

A large number of AIDS patients were suffering from the disease

42
Q

What is Cryptosporidium parvum and what are the symptoms of the disease it causes?

A
  • A protozoan parasite that infects the intestine of the host
  • It is a problem in the young, old, and immunocompromised
  • Symptoms:
    • Diarrhoea (10-15 litres per day)
    • Abdominal cramps
    • Headache
    • Fatigue
    • Mild fever
43
Q

Why are Cryptosporidium less accessible to factors that the host would normally use to control intracellular pathogens?

A

They live in an intracellular but extracytoplasmic location

44
Q

What are Cryptosporidium’s unique features?

A
  • Parasite develops just under the host epithelial cell membrane in an intracellular but extracytoplasmic position
  • The oocyst stages are fully formed when expelled from the host
  • There is no need for sporulation and therefore oocysts are immediately infective (auto-infection)
45
Q

What is the common coccidian sexual life cycle?

A
  • Multiple rounds of schizogony (depending on parasite species)
  • Microgamete (male) and macrogamete (female) form a zygote
  • Oocysts can sporulate in host or externally, depending on species
46
Q

What is Toxoplasma gondii, how is it spread, and what are the symptoms in humans?

A

An opportunistic parasite

Usually asymptomatic in adult humans

Toxoplasmosis is usually spread by eating poorly cooked food that contains the cysts

Can also contract it directly from cats

47
Q

What are the different life cycles of Toxoplasma gondii?

A
  • Takes place in the epithelium of the cats
  • Similar sexual cycle to Cryptosporidium
  • Direct (faecal-oral) life cycle can occur in cats
48
Q

What is the life cycle of Toxoplasma gondii in an intermediate host?

A
  • Any warm-blooded animal that injests oocysts can become infected
  • The parasite does not undergo sexual multiplication in the gut of intermediate hosts
  • Instead, it undergoes asexual (extra-intestinal) multiplication in any cell of the host as the tachyzoite stage for around 14 days
  • At 14 days post infection, the tachyzoites transform into bradyzoites. These form cysts in the muscle, brain, and eye
  • These cysts stages are long-lived and can initiate the sexual cycle when eaten by a cat or the asexual cycle when ingested by any other carnivore
49
Q

Why are incidences of Toxoplasma gondii higher in pregnant women in Paris than they are in pregnant women in Glasgow?

A

Parisian women eat a lot of almost-raw meat

50
Q

What are the differences in the Toxoplasma gondii symptoms in immunocompetent and immunocompromised humans, and congenital disease?

A

Immunocompetenet

  • Disease is usually slef-limiting but mild flu-like symptoms are common at onset
  • Cyst stages persist for life

Immunocompromised

  • Disease commonly manifests as severe encephalitis
  • Due to a new infection or reactivation of cyst stages from historic infection

Congenital disease

  • Women infected during pregnancy can transfer parasite to foetus
  • Congenital disease can be severe hydrocephalus, ocular lesions, mental retardation
51
Q

What is the treatment for infections of Toxoplasma gondii?

A
  • Sulphadiazine
  • Pyrimethamine
  • Spiromycin
52
Q

What causes malaria?

A

The obligate parasite Plasmodium

53
Q

How many cases of malaria were there in 2010? How many of these died?

A
  • 219-550 million cases
  • 660,000 - 1.24 million deaths
54
Q

Which species of Plasmodium infect man? Which is the most severe, and which is the most common?

A
  • P. falciparum (most severe)
  • P. vivax (most common)
  • P. ovale
  • P. malariae
  • P. knowlesi
55
Q

What does Plasmodium require?

A

Two hosts (obligate requirement)

56
Q

How does malaria spread between hosts?

A
  • Female Anopheles mosquite infected during blood meal
  • Male and female gametocytes ingested
  • Sexual reproduction occurs in stomach of mosquite
  • Infective sporozoites accumulate in the salivary glands of mosquito
  • Mosquito injects sporozites into next host during subsequent blood meal
57
Q

Explain the geographic distribution of malaria infections.

A
  • Limited but extensive geographic distribution
  • Dictated by natural habitat of Anopheles host
  • Population density, prevalence of childhood infection, ambient temperature and rainfall all play an important role
  • 80% of cases originate from sub-Saharan Africa
58
Q

What are the differences between P. falciparum and P. vivax infections?

A

P. falciparum

  • Potentially fatal – cerebral malaria
  • Very high parasitaemia
  • Drug resistance

P. vivax

  • Common, usually benign
  • Recurrent
59
Q

How can malaria be managed and controlled?

A
  • Diagnosis by microscopy of blood films
  • Treatment with chloroquine or quinine (++)
  • Eradicate liver forms in P. vivax
  • Prophylaxis for travellers
  • Avoid mosquito bites
  • Mosquito control
  • ?Vaccination – trying to develop
60
Q

Give a brief overview of the current state of malaria research.

A
  • Malaria funding has increased nearly 10-fold
  • Major gains have been made in controlling the disease in developing nations
    • Through interventions, including timely diagnosis and treatment, improved diagnostics, effective drugs, indoor spraying with long-lasting insecticides, bed nets treated with long-lasting insecticides
  • Current tools and treatments are insufficient to achieve elimination in many countries
  • Cost of maintaining these interventions is billions of dollars a year
  • Malaria parasite is developing resistance
  • Infected individuals who are asymptomatic remain an ongoing source of transmission
  • Microbiome impacts on mosquito gut

BS1040: Microbiology and Cell Biology (25 decks)

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