Block D Flashcards
respiratory viruses
influenza, rhinovirus, adenovirus, coronavirus.
Usually acquired by inhalation of droplets and replicated in the respiratory tract
enteric viruses
polio, rotaviruses, reoviruses, some adenoviruses.
Replicate in the gut, and cause gastric infections. Acquired by ingestion of faecal-contaminated material.
arboviruses
flaviruses, bunyaviruses and some rhabdoviruses. Infects insects that ingest vertebrate blood. Replicate in tissue of the insect and then transmitted to vertebrate host.
hepatitis viruses
all viruses that cause liver disease
sexually transmitted viruses
herpes simplex, papilloma viruses.
where do viruses replicate
only in certain types of cells or in whole organisms for which the virus has a tropism
what are the easiest viruses to grow
bacterial
what are the hardest viruses to grow
plant because study often requires growth of whole plant
what is titer
number of infectious units per volume of fluid
plaque assay
analogous to the bacterial colony; one way to measure virus infectivity
Plaques are clear zones that develop on lawns of host cells
Lawn can be bacterial or tissue culture
Each plaque results from infection by a single virus particle
what are naked viruses
viruses without membranes
what are capsids
nucleic acid packaged in protein coat found in virions
what are nucleocapsids
nucleic acid and protein packaged into a virus
what is lysozyme
enzyme that makes hole in cell wall, lyses bacterial cell
what is neuraminidases
enzymes that cleave glycosidic bonds, allows liberation of viruses from cell
virus replication
initiation- recognition, attachment, penetration, uncaring
replication- transcription, protein synthesis, genome replication, assembly
release- lysis and release, budding and release
epstein-barr virus
target cell= B cell
receptor= C3d complement receptor
HIV 1
target= helper T cell
receptor= CD4
rhinovirus
target= epithelial cell
receptor= ICAM-1
poliovirus
target= epithelial cell
receptor= immunoglobulin super family protein
herpes simplex virus
target= many cells
receptor= immunoglobulin super family protein
rabies virus
target= neuron
receptor= acetyl choline receptor
influenza A virus
target= epithelial cell
receptor= sialic acid
B19 virus (parvovirus)
target= erythroid precursors
receptor= erythrocyte P antigen
picornaviridae
virus= rhinovirus
viral attachment protein= VP1, VP2, VP3 complex
adenoviridae
virus= adenovirus
viral attachment protein= fibre protein
reovirdae
virus= reovirus, rotavirus
viral attachment protein= alpha-1, VP7
togavirdae
virus= semliki forest virus
viral attachment protein= E1, E2, E3 complex
rhabdovirdae
virus= rabies virus
viral attachment protein= G protein
orthomyxoviridae
virus= influenza A virus
viral attachment protein= HA
paramyxoviridae
virus= measles virus
viral attachment protein= HA
herpesviridae
virus= epstein-barr virus
viral attachment protein= gp350 and gp220
retroviridae
virus= HIV-1
viral attachment protein= gp120
what does it mean if the virus is smaller
its more dependent on host
where does DNA transcription occur
nucleus, except poxviruses
what is transcription regulated by
interaction of DNA binding proteins with regions of viral genome
what does genome replication initiate
transcription of late genes
what kind of energy conservation is DNA replication
semi-conservative
where does RNA replication occur
cytoplasm, except influenza
what can eukaryotic ribosomes not translate
polycistronic mRNA
what is a virus
genetic element that cannot replicate independently if a living host cell
what are virions
extracellular form of a virus, exists outside host and facilitates transmission from one host cell to another, contain nucleic acid genome surrounded by a protein coat
phases of viral replication
- Attachment (adsorption of phage virion)
- Penetration of viral nucleic acid
- Synthesis of viral nucleic acid
and protein - Assembly and packaging of new viruses
- Cell lysis and release of new virions
what is a permissive cell
host cell that allows the complete replication cycle of a virus to occur
attachment and entry of Bacteriophage T4
Virions attach to cells via tail fibers that interact with polysaccharides on E. coli cell envelope. Tail fibers retract, and tail core makes contact with E. coli cell wall. Lysozyme-like enzyme forms small pore in peptidoglycan. Tail sheath contracts, and viral DNA passes into cytoplasm
T4 genome
has a dsDNA genome that is circularly permuted and terminally redundant
what is the restriction modification system
DNA destruction system, effective only against double-stranded DNA viruses
what do restriction enzymes do
they leave DNA at specific sequences, modification of host’s own DNA at restriction enzyme recognition sites prevents cleavage of own DNA
what modified base does T4 DNA contain
5-hydroxymethylcytosine, its DNA is resistant to virtually all known restriction enzymes
what can the T4 genome be divided into
early, middle and late proteins
T4 genome early and middle proteins
enzymes needed for DNA replication and transcription
T4 genome late proteins
head and tail proteins and enzymes required to liberate mature phage particles
replication of bacteriophage T4 early proteins
enzyme for the synthesis and glucosylation of the T4 base hydroxymethylcytosine, enzymes that function in T4 replisome, proteins that modify host RNA polymerase
replication of bacteriophage T4 middle proteins
additional proteins that modify host RNA polymerase, production of viral proteins
replication of bacteriophage T4 late proteins
synthesised later, include proteins of virus coat, typically structural components, synthesised in larger amounts
packaging the T4 genome
packaging motor attaches to prohead, packaging motor is assembled, double-stranded DNA is pumped into head under pressure using ATP, after head is filled with DNA T4 tail, tail fibres and other components are added, packaging motor discarded
what is virulent mode
viruses lyse host cells after infection
what is temperate viruses
can undergo a stable genetic relationship within the host, but can also kill cells though lytic cycle
what is lysogeny
state where most virus genes are not expressed and virus genome (prophage) is replicated in synchrony with host chromosome
what is lysogen
a bacterium containing a prophage
bacteriophage lambda
linear dsDNA genome, Complementary, single-stranded regions 12 nucleotides long at the 5′ terminus of each strand.
Upon penetration, DNA ends base-pair, forming the cos site, and the DNA ligates and forms double-stranded circle
When lambda is lysogenic, its DNA integrates into E. coli chromosome at the lambda attachment site (attλ)
cI protein (the lambda repressor):
causes repression of lambda lytic events (Activates lysogeny)
Cro repressor
controls activation of lytic events (represses lysogenic genes)
transduction
transfer of DNA from one cell to another by bacteriophage due to mispackaging of the bacteriophage genome- drives bacterial evolution
Generalized transduction
DNA from any portion of the host genome is packaged inside the virion
Specialized transduction
DNA from a specific region of the host chromosome is integrated directly into the virus genome
what is entamoeba histolytica
a pathogenic protist transmitted to humans primarily though contaminated water and food
what is entamoeba histolytica disease called
amoebiasis
entamoeba histolytica non-invasive infection
intestinal disease, diarrhea, ulcers in colon
entamoeba histolytica invasive infection
extra-intestinal disease, abscess in liver, lung and brain
balantidium coli
ciliated, intestinal human and swine parasite. infections caused by cysts, transmitted to humans through faecally contaminated water
entamoeba histolytica treatment and diagnosis
azoles in particular metronidazole. cysts in stool
balantidium coli treatment and diagnosis
tetracycline, metronidazole, iodoquinol. in stool and colon tissue
Giardia intestinalis
Flagellated anaerobic parasite. Has mitosomes (mitochondrial remnant organelles). Produces highly resistant cysts - Cause of giardiasis, a common waterborne disease. Explosive, foul-smelling diarrhea, intestinal cramps, nausea, weight loss, and malaise . Many individuals exhibit no symptoms and can act as carriers
Giardia intestinalis diagnosis and treatment
cysts and trophozoites in faeces. metronidazole and tinidazole
Trichomonas vaginalis
Flagellated anaerobic parasite.
Transmitted person-to-person by sexual intercourse. Can survive on moist surfaces:
Can be transmitted by toilet seats, sauna benches,
and towels . Mostly asymptomatic in males . Vaginal purulent discharge, itching, and burning in women
Trichomonas vaginalis diagnosis and treatment
microscopy and cell culture from patient secretions. metronidazole
Cryptosporidium parvum
Protist (Apicomplexa) lives as a parasite in warm-blooded animals, causes diarrhoea.
Produces thick-walled cells (oocysts) that are shed in the faeces of infected animals
The oocysts are transmitted in faecally contaminated water (e.g. swimming pools)
Oocysts are highly resistant to chlorine
and UV radiation; thus, sedimentation
and filtration methods are most effective
at removal
Toxoplasma gondii
Apicomplexan protist that lives as a parasite in warm-blooded animals
Life cycle is similar to Cryptosporidium parvum with the same intermediate stages
Produces oocysts that are shed in the faeces of infected animals
The oocysts are transmitted by cats (also by undercooked meat)
Toxoplasmosis is mainly asymptomatic
Toxoplasma can damage eyes, brain, and other organs in
immune-compromised individuals
Toxoplasma can cause birth defects
Treatment: Sulphadiazine and Pyrimethamine; Spiromycin
Naegleria fowleri
A free-living amoeba found in soil and water
Infections usually result from swimming in warm, soil-contaminated water sources (e.g., hot springs or lakes)
Enters the human body through the nose and
burrows directly into the brain, causing extensive
hemorrhage and brain damage (meningoencephalitis)
In most cases fatal
Naegleria fowleri diagnosis and treatment
Diagnosis from cerebrospinal fluid
Drug treatment is only effective if infections are
identified early. Azoles, amphotericin B, rifampicin, and
miltefosine
Acanthamoeba
Many species (e.g. castellani, polyphaga and culburtsoni)
found in fresh and salt water throughout the world
Infection through contaminated 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
Disease caused:
- Eye Disease: Acanthamoeba keratitis (AK)
- Cutaneous Amoebiasis: Skin Disease
- Brain Disease: Granulomatous Amoebic Encephalitis (GAE)
Acanthamoeba diagnosis and treatment
Diagnosis by microscopic examination of tissue samples
Treatment with azoles, amphotericin B, rifampicin, and
miltefosine (same as for Naegleria)
Acanthamoeba keratitis (AK)
Progressive sight-threatening corneal disease
The leading risk factor is contact lens wear
Most common type of Acanthamoeba infection
Treatment is not always successful and corneal transplants are often required
Reactivation often occurs in transplanted cornea
Malaria
Caused by the apicomplexan parasite Plasmodium
Complex life cycle including Anopheles mosquitoes as vectors
~350 million people infected worldwide
Each year over 1 million people die from malaria
Generally found in tropical and subtropical regions
Plasmodium and Malaria
Diagnosis requires identifying Plasmodium-infected erythrocytes
in blood smears by microscopy
Drugs are used to prevent and treat infections
e.g. chloroquine and mefloquine (Lariam), pyrimethamine, doxycycline, clindamycin
Malaria may recur years after the primary infection
Several vaccines are currently in development
Can be controlled by draining swamps or eliminating mosquitoes
Leishmania
Flagellated protozoan
Causes cutaneous, mucocutaneous
or visceral leishmaniasis
Transmitted by bite of sand fly
Infects and grows in macrophages
Diagnosis: Microscopy of tissue specimen
PCR, serology
Leishmania mexicana
Causes cutaneous leishmaniasis
Forms nodules and ulcers on skin
Treatment with pentavalent antimonial
compounds, amphotericin B, miltefosine
Leishmania braziliensis
Causes mucocutaneous leishmaniasis (South America)
Parasite destroys mucosa and cartilage of mouth, nose and throat
If untreated, mucocutaneous disease can be fatal
Treatment with pentavalent antimonial compounds, amphotericin B, miltefosine
Leishmania donovani
Causes visceral leishmaniasis (VL)
Parasite travels to internal organs
Damage to liver, spleen, and bone marrow
If untreated, visceral disease is fatal
Recovery possible but occasionally relapse occurs (post-kala-azar dermal leishmanoid; PKDL)
Treatment with pentavalent antimonial compounds, amphotericin B, miltefosine
Trypanosoma brucei
Two subspecies
T. brucei gambiense
T. brucei rhodesiense
Causes African sleeping sickness (Human African trypanosomiasis; HAT); 55 million at risk; 300,000 cases/year
Transmitted by bite of tsetse fly
Parasite multiplies in blood
Intermittent fever during early stages of infection (stage I)
Trypanosoma brucei stage 2
Leeds to inflammation of brain tissue and necrosis
Diagnosis by spinal puncture and microscopy of cerebro-spinal fluid
Requires hospitalisation
Meningoencephalitic stage, invasion of the central nervous system with headaches, somnolence, abnormal behavior, lethargy, loss of consciousness and coma
Treatment with suramin, melarsoprol, pentamidine,
eflornithine
Trypanosoma cruzi
Causes Chagas’ disease (American trypanosomiasis)
Transmitted by bite and defaecation of “kissing bug“ (Triatomine bug)
Parasite affects heart, gastrointestinal tract, and central nervous system
Occurs in Latin American countries
Diagnosis by microscopy or serology
Treatment with nifurtimox (Lampit) and benznidazole (Radanil)
