Lecture 2- Viruses And Protozoa Flashcards
Attachment
Attachment, penetration, synthesis + release= stages of a viral infection
Attachment=
-viral proteins on the capsid or envelope bind to specific protein receptors; cell surface receptors facilitate viral entry
-receptors have other cellular functions; exploited by the virus and viral receptors bind to carbohydrate components
Specificity
-some viruses are highly host specific; small pox virus and human specialist
-influenza A; wide range of mammals and birds
-specificity it’s important in the case of immunisation
Synthesis
-synthesis of viral proteins in cytoplasm
-replication of viral genome; DNA viruses typically replicate in nucleus, RNA viruses replicate in cytoplasm
-assembly of progeny virus particles
Release/Exit
*lysis
-naked viruses and pox viruses leave cell by rupturing the cell membrane
-usually results in death of the host cell
*budding
-enveloped viruses, envelope contains host lipids and carbohydrates
-host cell does may not die
Viral diseases
2 aspects
1. Transmission - host to host transport
2. Symptoms- cellular impacts
Symptom generation
-cell destruction
-changes to gene expression
-immune response degradation
Infection
-through a break in the mucous membranes; mouth or throat, cold sores
-via the eye/genitals= genital herpes
-directly via minor abrasions in the skin; herpes whitlow, herpes gladiatorum
Reactivation and latency + symptoms
-when latent viral DNA is not integrated into host genome= limited expression of viral genes
-reactivation due to= physical (e.g. injury UV light, hormones)
-psychological (e.g. stress, emotional upset)
Symptoms:
-fluid filled vesicles
-more dangerous in the immunocompromised
Poxviridae
-causes diseases in vertebrates and invertebrates
-smallpox; large complex virus
-cowpox
-monkeypox
RNA viruses
• Poliovirus
• Norovirus
• Influenza
• Rotavirus
• Hantavirus
• Ebola
• Coronaviruses (CoVs)
Poliovirus and Poliomyelitis
Poliovirus= enterovirus
- + stranded RNA virus
-naked
-immunisation
-WHO eradication programme
Poliomyelitis= poliovirus- transmitted by ingestion
Initial symptoms= sore throat and nausea
-viremia may occur; if persistent —> enters the CNS = destruction of motor cells and paralysis occurs
Prevention= vaccination
Retrovirus
-DNA becomes integrated into the host chromosome
-retrovirus DNA = transcribed to yield mRNA
-may retain in a latent state within the cells; provirus
Problems with antivirals
-identification of virus-specific target
-generation of resistant variants
Protozoa;
Parasite vs Pathogen
Not always clear if Protozoa are parasites or pathogens
-insect transmitted = more likely parasites
(Systemic long-term infections, intracellular phase + hard to treat)
-pathogens= often faecal oral transmitte (shorter term diseases)
Faecal oral transmission
-giardia= found in intestinal tracts of animals + environment
-amoebic dysentery
-cryptosporidium
Acanthamoeba and Naegleria
Acanthamoeba sp
= damages cornea and can cause fatal encephalitis
Trichomonas vaginalis
-most common protozoan causing human disease
-lives in the genitourinary system of men + women
-transmitted almost exclusively via sex
-infection in women = vaginitis
-infection in men= asymptomatic
Toxoplasma
T.gondii = causative agent of toxoplasmosis
-widely distributed parasites
-wild + domestic mammals and birds are major reservoir
-infection due to= consumption of undercooked meat containing the parasite + ingestion/inhalation of contaminated soil
-protozoan can cross the placenta + infection the foetus
Toxoplasma gondii
-most infections = asymptomatic
-toxoplasmosis = only in small number of people; fever-producing illness combined with other symptoms + self-limited infection
-toxoplasmosis= more severe in AIDS patients + foetus
Trypanosoma Cruzi
-causes Chagas’ disease
-endemic in central+ South America
-opossums + armadillos = primary reservoir
-transmission = bite of insects in genus triatoma
- “kissing bugs” = feed preferentially from blood vessels in the lip
-parasite-induced heart disease = cause of death in Latin America
Trypanosoma brucie
Trypanosoma brucei
• Causes African sleeping sickness
• The insect vector is the tsetse fly
• Three stages;
• Site of the fly bite becomes a lesion with dead tissue
• Fever, lymph node swelling, and headaches
• Meningoencephalitis
• Infections characterized by cyclical waves of infection
• Clearing tsetse fly habitats reduce the cases of disease
Leishmania
-causes leishmaniasis
-endemic in parts of the tropical and subtropics
-common hosts =wild +domestic dogs and small rodents
-transmitted by= sand flies
Plasmodium
-causative agent of malaria
-4 species cause malaria= p.falciparum, p.vivax, p.ovale and p.malariae
-malaria= endemic throughout the tropics + subtropics
-mosquitos= vector
-3 prominent stages
Malaria vaccine
2 vaccines = target the first stage of the parasites lifecycle before it gets to the liver
-built using= proteins from the malaria
