Microbiology Exam 3

Compromised host

: an individual whose resistance to infection is impaired by disease, therapy, or burns

Compare Bacteriophage and animal virus life cycles Attachment - Entry- Uncoating - Biosynthesis- chronic infection - release

Bacteriophages ◦ Attachment - Tail fibers attach to cell wall proteins ◦ Entry - Viral DNA is injected into host cell ◦ Uncoating - Not required ◦ Biosynthesis - in cytoplasm ◦ Chronic infection - lysogeny ◦ Release - host cell is lysed • Animal Viruses ◦ Attachment sites are plasma membrane proteins and glycoproteins ◦ Entry - Capsid enters by receptor - mediated endocytosis or fusion ◦ Uncoating Enzymatic removal of capsid proteins ◦ Biosynthesis - in nucleus (DNA viruses or cytoplasm (RNA viruses ◦ Chronic infection - Latency - slow viral infections; cancer ◦ Release - enveloped viruses bud out; non-enveloped viruses rupture plasma membrane

three methods of disease transmission.

Contact Transmission vehicle transmission Vector transmission (Mechanical or Biological

Comparison of Endotoxin and Exotoxins Produced by Bacteria

Endotoxin Gram-negative bacteria Lipid A component of lipopolysaccharide Effect on host - General systemic symptoms of inflammation and fever Heat stable LD50 - High Exotoxin Gram-positive (primarily) and gram-negative bacteria Protein Specific damage to cells dependent upon receptor-mediated targeting of cells and specific mechanisms of action Most are heat labile, but some are heat stable LD50 - Low

Contrast normal microbiota and transient microbiota with opportunistic microorganisms.

Normal microbiota and transient microbiota can also be opportunist microorganisms when they are in different environments than normal or the host's immune system is suppressed. Opportunistic microorganisms do not have to have a permanent residence in the host.

Explain how viruses acquire an envelope

Viral proteins that are to become spikes of virus attach to the host plasma membrane; 2) the inside of the plasma membrane becomes coated with the matrix protein of the virus; 3) nucleocapsid becomes enclosed by viral envelope which is composed of the host's plasma membrane. - Most enveloped viruses obtain their envelopes as they exit the cell through the plasma membrane. Some, however, bud through the Golgi apparatus or rough endoplasmic reticulum. - For all enveloped viruses, budding is part of the maturation process. The process of budding may not lead to cell death, because the plasma membrane can be repaired following budding.

morbidity

a state of illness ◦ Morbidity or total morbidity is expressed in numbers of individuals without reference to the size of the population.

prions

acellular infectious particle consisting of just proteins that can cause progressive diseases in animals and humans ◦ The protein PrP is found in our bodies. ◦ A prion is a misfolded rogue form of a normal protein (PrPc) found in the cell ◦ may be caused by a genetic mutation or occur spontaneously, can be infectious, stimulating other endogenous normal proteins to become misfolded, forming plaques ◦ The prions can join together to form rods that accumulate in the brain causing tissue damage, cells death, loss of neurons, and amyloid plaques (neurodegeneration) ◦ The newly produced PrPSc molecules convert more normal molecules to the abnormal form through unknown mechanism

lysogenic conversion (phage conversion)

alteration of host characteristics or phenotypes due to the presence of phage ◦ The presence of the phage may alter the phenotype of the bacterium, since it can bring in extra genes (e.g., toxin genes that can increase bacterial virulence). This change in the host phenotype

Baltimore classification system

an alternative to ICTV nomenclature. The Baltimore system classifies viruses according to their genomes (DNA or RNA, single versus double stranded, and mode of replication). This system thus creates seven groups of viruses that have common genetics and biology.

pandemic disease

an epidemic that is worldwide as opposed to regional ◦ HIV/AIDS is a pandemic disease and novel influenza virus strains often become pandemic.

epidemic disease

an illness with a higher-than- expected incidence in a given period within a given population ◦ Diseases for which a larger than expected number of cases occurs in a short time within a geographic region ◦ Influenza is a good example of a commonly epidemic disease. Incidence patterns of influenza tend to rise each winter in the northern hemisphere. These seasonal increases are expected, so it would not be accurate to say that influenza is epidemic every winter; however, some winters have an usually large number of seasonal influenza cases in particular regions, and such situations would qualify as epidemics ◦ An epidemic disease signals the breakdown of an equilibrium in disease frequency, often resulting from some change in environmental conditions or in the population

International Committee on Taxonomy of Viruses (ICTV)

are not classified in the three domains of life - Since viruses can mutate so quickly, it can be difficult to classify the ICTV's viral nomenclature system classifies viruses into families and genera based on viral genetics, chemistry, morphology, and mechanism of multiplication. Viral family names end in -viridae (e.g, Parvoviridae) and genus names end in −virus (e.g., Parvovirus). • Viral genomes can be circular, linear or segmented

Describe viral genomes

based on chemistry, morphology, or other characteristics they share in common. Categories may include naked or enveloped structure, single-stranded (ss) or double-stranded (ds) DNA or ss or ds RNA genomes, segmented or nonsegmented genomes, and positive-strand (+) or negative-strand (−) RNA. Other characteristics such as host specificity, tissue specificity, capsid shape, and special genes or enzymes may also be used to describe groups of similar viruses • Viral genomes can be circular, linear or segmented

plaque

clear area on bacterial lawn caused by viral lysis of host cells - lytic bacteriophages • Animal viruses require cells within a host animal or tissue-culture cells derived from an animal.

mortality

death ◦ the incidence and prevalence of mortality (death) may also be reported. A mortality rate can be expressed as the percentage of the population that has died from a disease or as the number of deaths per 100,000 persons (or other suitable standard number)

lysis

destruction of the host cell

The Lytic Cycle

infection process that leads to the lysis of host cells ▪ During the lytic cycle of virulent phage, the bacteriophage takes over the cell, reproduces new phages, and destroys the cell. T-even phage is a good example of a well-characterized class of virulent phages. There are five stages in the bacteriophage lytic cycle

Viroids (virus-like)

infectious plant pathogen composed of RNA ◦ Acellular particle that's NOT a virus ◦ Smallest known infectious agents ◦ consist only of a short strand of circular RNA capable of self- replication. ◦ viroids do not have a protein coat to protect their genetic information. ◦ Viroids can result in devastating losses of commercially important agricultural food crops grown in fields and orchards. ◦ can be dispersed mechanically during crop maintenance or harvesting, vegetative reproduction, and possibly via seeds and insects, resulting in a severe drop in food availability and devastating economic consequences.

in vivo

inside the organism - Viruses

bacterial lawn

layer of confluent bacterial growth on an agar plate - Bacteriophages

two categories of viruses based on general composition

naked viruses or nonenveloped viruses and enveloped viruses

in vitro

outside the organism in a test tube or artificial environment - Viruses

prophage

phage genome that has incorporated into the host genome

two aspects of morbidity that are relevant to an epidemiologist

prevalence and incidence of disease

• capsid

protein coat surrounding the genome of the virus ◦ The interior contains the bare necessities in terms of genome and enzymes needed to direct the synthesis of new virions

biosynthesis

replication of viral genome and other protein components ◦ The third stage of infection. After entering the host cell, the virus synthesizes virus-encoded endonucleases to degrade the bacterial chromosome. It then hijacks the host cell to replicate, transcribe, and translate the necessary viral components (capsomeres, sheath, base plates, tail fibers, and viral enzymes) for the assembly of new viruses. Polymerase genes are usually expressed early in the cycle, while capsid and tail proteins are expressed later.

virusoids

small piece of RNA associated with larger RNA of some infectious plant viruses ◦ pathogenic RNA that can infect commercially important agricultural crops ◦ subviral particles best described as non-self-replicating ssRNAs ◦ virusoids require that the cell also be infected with a specific "helper" virus ◦ There are currently only five described types of virusoids and their associated helper viruses. The helper viruses are all from the family of Sobemoviruses. ◦ Once the helper virus enters the host cell, the virusoids are released and can be found free in plant cell cytoplasm, where they possess ribozyme activity. The helper virus undergoes typical viral replication independent of the activity of the virusoid. The virusoid genomes are small, only 220 to 388 nucleotides long. A virusoid genome does not code for any proteins, but instead serves only to replicate virusoid RNA. ◦ Virusoids belong to a larger group of infectious agents called satellite RNAs ▪ satellite RNAs may encode for proteins; however, like plant virusoids, satellite RNAs must coinfect with a helper virus to replicate.

tissue tropism

tendency of most viruses to infect only certain tissue types within a host

morbidity rate

the number of cases of a disease expressed as a percentage of the population or number per standard part of the population, such as 100,000 ◦ or as a percent of the population.

Define epidemiology.

the study of where and when infectious diseases occur in a population and how they are transmitted and maintained in nature ◦ goal of recognizing and controlling outbreak ◦ includes etiology

host range

the types of host cells that a particular virus is able to infect

latent virus

virus that remains dormant in the host genome ◦ viruses capable of latency may initially cause an acute infection before becoming dormant. • latent virus virus that remains dormant in the host genome ◦ Latent viruses may remain dormant by existing as circular viral genome molecules outside of the host chromosome. Others become proviruses by integrating into the host genome. During dormancy, viruses do not cause any symptoms of disease and may be difficult to detect. A patient may be unaware that he or she is carrying the virus unless a viral diagnostic test has been performed.

polyhedral virus

with a three-dimensional shape with many facets ◦ Polyhedral capsids form the shapes of poliovirus and rhinovirus, and consist of a nucleic acid surrounded by a polyhedral (many- sided) capsid in the form of an icosahedron.

Know the steps of viral replication for animal cells

• 1.) Adsorption - attachment to host cell • 2.) Penetration - viral particle enters host cell • 3.) Uncoating - capsid is broken down to release viral genome into cytoplasm • 4.) Biosynthesis - host cell makes new viral genomes and proteins • 5.) Assembly - viral genomes are packaged into newly formed capsids • 6.) Release - viruses leave host cell to infect other cells

biological vector an

• animal (typically an arthropod) that is infected with a pathogen and is capable of transmitting the pathogen from one host to another ◦ Most arthropod vectors transmit the pathogen by biting the host, creating a wound that serves as a portal of entry ◦ There are also important non-arthropod vectors of disease, including mammals and birds. Various species of mammals can transmit rabies to humans, usually by means of a bite that transmits the rabies virus. Chickens and other domestic poultry can transmit avian influenza to humans through direct or indirect contact with avian influenza virus A shed in the birds' saliva, mucous, and feces.

vector

• animal (typically an arthropod) that transmits a pathogen from one host to another host; DNA molecules that carry DNA fragments from one organism to another ◦ Arthropods such as mosquitoes, ticks, and flies, are typical vectors for viral diseases

maturation

• assembly of viral components to produce a functional virus ◦ new virions are created. To liberate free phages, the bacterial cell wall is disrupted by phage proteins such as holin or lysozyme.

lysogen

• bacterium carrying the prophage

Microbial antagonism -

• competition between microbes

droplet transmission

• direct contact transmission of a pathogen transferred in sneezed or coughed droplets of mucus that land on the new host within a radius of one meter ◦ Transmission over distances greater than one meter is called airborne transmission.

penetration

• entry of phage or virus into a host cell through injection, endocytosis, or membrane fusion ◦ The second stage of infection. This occurs through contraction of the tail sheath, which acts like a hypodermic needle to inject the viral genome through the cell wall and membrane. The phage head and remaining components remain outside the bacteria.

sporadic disease

• illness that occurs at relatively low levels with no discernible pattern or trend, frequently with no geographic focus ◦ Examples of sporadic diseases include tetanus, rabies, and plague ◦ In the United States, Clostridium tetani, the bacterium that causes tetanus, is ubiquitous in the soil environment, but incidences of infection occur only rarely and in scattered locations because most individuals are vaccinated, clean wounds appropriately, or are only rarely in a situation that would cause infection.[3] Likewise in the United States there are a few scattered cases of plague each year, usually contracted from rodents in rural areas in the western states

capsomere

• individual protein subunits that make up the capsid ◦ made of one or more different types of proteins that interlock to form the closely packed capsid

viral envelope

• lipid membrane obtained from phospholipid membranes of the cell that surrounds the capsid ◦ obtained as the virion buds from a host cell. The viral envelope may either be intracellular or cytoplasmic in origin.

tail fiber

• long protein component on the lower part of a phage used for specific attachment to bacterial cell

transient microbiota

• microorganisms, sometimes pathogenic, that are only temporarily found in the human body

Contact transmission

• movement of a pathogen between hosts due to contact between the two; may be direct or indirect

biological transmission

• movement of a pathogen between hosts facilitated by a biological vector in which the pathogen grows and reproduces

horizontal direct transmission

• movement of a pathogen from one host to another (excluding mother to embryo, fetus, or infant) in a population through physical contact or through droplet transmission ◦ Often, contact between mucous membranes is required for entry of the pathogen into the new host, although skin-to-skin contact can lead to mucous membrane contact if the new host subsequently touches a mucous membrane. Contact transmission may also be site-specific; for example, some diseases can be transmitted by sexual contact but not by other forms of contac

vehicle transmission transfer

• of a pathogen between hosts via contaminated food, water, or air ◦ longer distance transmission of droplets through the air

sheath

• part of the tail on a bacteriophage that contracts to introduce the viral DNA into the bacterium ◦ In the bacteriophage complex form, the genome is located within the polyhedral head and the sheath connects the head to the tail fibers and tail pins that help the virus attach to receptors on the host cell's surface. Poxviruses that have complex shapes are often brick shaped, with intricate surface characteristics not seen in the other categories of capsid.

Normal microbiota

• permanently colonize the host and do not cause disease under normal conditions • Human Microbiome Project analyzes relationships between microbial communities on the body and human health Distribution and composition of normal microbiota are determined by many factors ◦ Nutrients ◦ Physical and chemical factors ◦ Host defenses ◦ Mechanical factors Normal microbiota protect us by: ◦ competing for nutrients ◦ secreting substances harmful to invaders ◦ changing pH and oxygen levels • The relationship between the host and normal microbiota is called symbiosis

tail pins

• points extended at the base of a bacteriophage sheath that, along with tail fibers, lead to phage attachment to a bacterial cell

retrovirus

• positive ssRNA virus that produces and uses reverse transcriptase to make an ssDNA copy of the retroviral genome that can then be made into dsDNA and integrate into the host cell chromosome to form a provirus within the host chromosome. ◦ alternative mechanism for viral nucleic acid synthesis

lysogeny

• process of integrating the phage into the host genome

induction

• prophage DNA is excised from the bacterial genome ◦ During lysogeny, the prophage will persist in the host chromosome until induction, which results in the excision of the viral genome from the host chromosome. After induction has occurred the temperate phage can proceed through a lytic cycle and then undergo lysogeny in a newly infected cell

virus specificity

• specific kinds of cells a virus can infect determined by specific host attachment sites and cellular factors

incidence

• the number of individuals with new infections of a particular disease in a given period of time

etiologic agent

• the pathogen or substance responsible for causing a particular disease; causative agent • It is not enough to observe an association between a disease and a suspected pathogen; controlled experiments are needed to eliminate other possible causes.

etiology

• the science of the causes of disease ◦ Investigation of disease transmission (mechanisms by which a disease is spread).

prevalence

• the total number or proportion of individuals in a population ill with a specific disease - at point in time

host range

• the types of host cells that a particular virus is able to infect

vertical direct transmission

• transfer of a pathogen from mother to child during pregnancy, birth, or breastfeeding

Indirect contact transmission

• transfer of an infectious agent between hosts through contact with a fomite ◦ involves inanimate objects called fomites that become contaminated by pathogens from an infected individual or reservoir ◦ Transmission occurs indirectly when a new susceptible host later touches the fomite and transfers the contaminated material to a susceptible portal of entry. Fomites can also include objects used in clinical settings that are not properly sterilized, such as syringes, needles, catheters, and surgical equipment. Pathogens transmitted indirectly via such fomites are a major cause of healthcare-associated infections

spike

• viral glycoprotein embedded within the viral capsid or envelope used for attachment to host cells ◦ Extending outward and away from the capsid on some naked viruses and enveloped viruses are protein structures At the tips of these spikes are structures that allow the virus to attach and enter a cell, like the influenza virus hemagglutinin spikes (H) or enzymes like the neuraminidase (N) influenza virus spikes that allow the virus to detach from the cell surface during release of new virions. Influenza viruses are often identified by their H and N spikes.

helical

• virus cylindrical or rod shaped ◦ tobacco mosaic virus (TMV), a naked helical virus, and Ebola virus, an enveloped helical virus. The capsid is cylindrical or rod shaped, with the genome fitting just inside the length of the capsid.

complex

• virus shape that often includes intricate characteristics not seen in the other categories of capsid

bacteriophage

• virus that infects bacteria

Describe the general characteristics of viruses as pathogens (host range & viral spread)

• viruses can infect every type of host cell, including those of plants, animals, fungi, protists, bacteria, and archaea. Viruses may cause abnormal growth of the cell or cell death, alter the cell's genome, or cause little noticeable effect in the cell. ◦ having a wide host range is not common and viruses will typically only infect specific hosts and only specific cell types within those host

Robert Koch

• was the first scientist to specifically demonstrate the causative agent of a disease (anthrax) ◦ Koch developed four criteria, now known as Koch's postulates, which had to be met in order to positively link a disease with a pathogenic microbe. Without Koch's postulates, the Golden Age of Microbiology would not have occurred. Between 1876 and 1905, many common diseases were linked with their etiologic agents, including cholera, diphtheria, gonorrhea, meningitis, plague, syphilis, tetanus, and tuberculosis. Today, we use the molecular Koch's postulates, a variation of Koch's original postulates that can be used to establish a link between the disease state and virulence traits unique to a pathogenic strain of a microbe.

transmissible spongiform encephalopathy

•- degenerative disease caused by prions; leads to the death of neurons in the brain

naked virus/ nonenveloped

•- virus composed of a nucleic acid core, either DNA or RNA, surrounded by a capsid

icosahedral three

•-dimensional, 20-sided structure with 12 vertices ◦ These capsids somewhat resemble a soccer ball

healthcare-associated infection (HAI)

•an infection acquired in a hospital or other health-care facility unrelated to the reason for which the patient was initially admitted; nosocomial infection ◦ HAIs are often connected with surgery or other invasive procedures that provide the pathogen with access to the portal of infection. ◦ In these settings, patients suffering from primary disease are often afflicted with compromised immunity and are more susceptible to secondary infection and opportunistic pathogens. ◦ Hospitals, retirement homes, and prisons attract the attention of epidemiologists because these settings are associated with increased incidence of certain diseases. Higher rates of transmission may be caused by characteristics of the environment itself, characteristics of the population, or both. Consequently, special efforts must be taken to limit the risks of infection in these settings

Mechanical transmission

•mechanical transmission transfer of a pathogen between hosts by a mechanical vector

Know mechanisms of virus cultivation

◦ A primary cell culture is freshly prepared from animal organs or tissues. Cells are extracted from tissues by mechanical scraping or mincing to release cells or by an enzymatic method using trypsin or collagenase to break up tissue and release single cells into suspension ▪ primary cell cultures require a liquid culture medium in a Petri dish or tissue-culture flask so cells have a solid surface such as glass or plastic for attachment and growth. Primary cultures usually have a limited life span. ◦ To prevent contact inhibition, cells from the primary cell culture must be transferred to another vessel with fresh growth medium. This is called a secondary cell culture. ◦ Continuous cells are not affected by contact inhibition

Release / lysis

◦ Mature viruses can either burst out of the host cell in a process called lysis when progeny viruses are liberated it into the environment to infect new cells

provirus

◦ Part of the retroviruses - after reverse transcriptase makes ssDNA - ssDNA then made into dsDNA- animal virus genome that has integrated into the host chromosome

mechanical vector

◦ an animal that transfers a pathogen from one host to another or from a reservoir to a host without being infected by the pathogen itself ▪ or example, a fly may land on fecal matter and later transmit bacteria from the feces to food that it lands on; a human eating the food may then become infected by the bacteria, resulting in a case of diarrhea or dysentery

reverse transcriptase

◦ enzyme found in retroviruses that can make a copy of ssDNA from ssRNA

direct contact transmission

◦ movement of a pathogen between hosts by physical contact or transfer in droplets at a distance less than one meter ▪ through actions such as touching, kissing, sexual intercourse, or droplet sprays. Direct contact can be categorized as vertical, horizontal, or droplet transmission

The Lysogenic Cycle

◦life cycle of some phages in which the genome of the infecting phage is integrated into the bacterial chromosome and replicated during bacterial reproduction until it excises and enters a lytic phase of the life cycle • the phage genome also enters the cell through attachment and penetration. • During the lysogenic cycle, instead of killing the host, the phage genome integrates into the bacterial chromosome and becomes part of the host • As the bacterium replicates its chromosome, it also replicates the phage's DNA and passes it on to new daughter cells during reproduction. • The phages infecting these bacteria carry the toxin genes in their genome and enhance the virulence of the host when the toxin genes are expressed.

mechanical vectors

• an animal that transfers a pathogen from one host to another or from a reservoir to a host without being infected by the pathogen itself

endemic disease

• an illness that is constantly present (often at low levels) in a population ◦ malaria is endemic to some regions of Brazil, but is not endemic to the United States.

Attachment

binding of phage or virus to host cell receptors ◦ the first stage in the infection process in which the phage interacts with specific bacterial surface receptors. Most phages have a narrow host range and may infect one species of bacteria or one strain within a species. This unique recognition can be exploited for targeted treatment of bacterial infection by phage therapy or for phage typing to identify unique bacterial subspecies or strains.

Know the three methods of viral entry (bacteria and animal cell entry)

• Bacteriophages inject DNA into the host cell ◦ Bacterial - Generalized transduction - Transfer of a specific piece of bacterial chromosomal DNA near the site of integration by the phage - lytic cycle ◦ Bacterial - Specialized transduction - transfer of a specific piece of bacterial chromosomal DNA near the site of integration by the phage - occurs at the end of the lysogenic cycle when the prophage is excised and the bacteriophage enters the lytic cycle • (Animal viruses) Membrane Fusion - viral membrane fuses with host membrane releasing nucleocapsid into cell - entry of enveloped virus • (Animal viruses) endocytosis the uptake of molecules through plasma membrane invagination and vacuole/vesicle formation - non-enveloped viruses

Describe the general structure of a virus

• In general, virions (viral particles) are small and cannot be observed using a regular light microscope. They are much smaller than prokaryotic and eukaryotic cells; this is an adaptation allowing viruses to infect these larger cells

Identify Characteristics of a Virus

• Infectious, acellular pathogens • Obligate intracellular parasites with host and cell-type specificity DNA or RNA genome (never both) • Genome is surrounded by a protein capsid and, in some cases, a phospholipid membrane studded with viral glycoproteins • Lack genes for many products needed for successful reproduction, requiring exploitation of host-cell genomes to reproduce acellular not made of cells ◦ not included in the tree of life because acellular • In order to survive and reproduce, viruses must infect a cellular host, making them obligate intracellular parasites. • virion inert particle that is the reproductive form of a virus ◦ The genome of a virus enters a host cell and directs the production of the viral components, proteins and nucleic acids, needed to form new virus particles called virions. New virions are made in the host cell by assembly of viral components. The new virions transport the viral genome to another host cell to carry out another round of infection

Know the two ways of viral release

• Nonenveloped viruses lyse host cells ◦ Viral proteins attack the membrane leading to lysis • Enveloped viruses use budding not lysis ◦ Viral proteins become incorporated into the host membrane • Sometimes viruses are released directly into a new host cell

Know how plant viruses are transmitted

• Plant viruses are more similar to animal viruses than they are to bacteriophages • Plant viruses may be enveloped or non-enveloped. can have either a DNA or RNA genome and be single stranded or double stranded. However, most plant viruses do not have a DNA genome; the majority have a +ssRNA genome, which acts like messenger RNA (mRNA). . • Most plant viruses are transmitted by contact between plants, or by fungi, nematodes, insects, or other arthropods that act as mechanical vectors. However, some viruses can only be transferred by a specific type of insect vector; for example, a particular virus might be transmitted by aphids but not whiteflies. In some cases, viruses may also enter healthy plants through wounds, as might occur due to pruning or weather damage. • Viruses that infect plants are considered biotrophic parasites, which means that they can establish an infection without killing the host. Viral infection can be asymptomatic (latent) or can lead to cell death (lytic infection). The life cycle begins with the penetration of the virus into the host cell. Next, the virus is uncoated within the cytoplasm of the cell when the capsid is removed. Depending on the type of nucleic acid, cellular components are used to replicate the viral genome and synthesize viral proteins for assembly of new virions. To establish a systemic infection, the virus must enter a part of the vascular system of the plant, such as the phloem. The time required for systemic infection may vary from a few days to a few weeks depending on the virus, the plant species, and the environmental conditions. The virus life cycle is complete when it is transmitted from an infected plant to a healthy plant.

two methods of viral replication in bacteria

• The Lysogenic Cycle • The Lytic Cycle

Compare Bacteriophage and animal virus life cycles

• The mechanisms of penetration, nucleic-acid biosynthesis, and release differ between bacterial and animal viruses. • After binding to host receptors, animal viruses enter through endocytosis (engulfment by the host cell) or through membrane fusion (viral envelope with the host cell membrane). • Many viruses are host specific, meaning they only infect a certain type of host; and most viruses only infect certain types of cells within tissues. This specificity is called a tissue tropism.

Explain how viruses are linked to cancers (oncogenic viruses)

• Virus invades host cell and viral genome integrates in host genome to produce provirus • Protooncogene - host gene that helps host cells grow • Oncogene - a host gene that causes cancer ◦ Oncogenes are mutated forms of protooncogenes • Viral genome integration near a protooncogene can lead to overexpression of the protooncogene which leads to increased cell division and tumor growth • Viral genome already contains an overactive oncogene ◦ Integration after infection automatically results in an oncogene in the host genome

notifiable disease

• a disease for which all cases must legally be reported to regional, state, and/or federal public health agencies

emerging infectious disease

• a disease that is new to the human population or has increased in prevalence over the previous 20 years ◦ Whether the disease is new or conditions have changed to cause an increase in frequency, its status as emerging implies the need to apply resources to understand and control its growing impact. ◦ Emerging diseases may change their frequency gradually over time, or they may experience sudden epidemic growth. ◦ Ebola - aware of the Ebola virus since the 1970s - The pattern of small isolated human epidemics changed in 2014

reemerging infectious disease

• a disease that was once under control or largely eradicated that has begun causing new outbreaks due to changes in susceptible populations, the environment, or the pathogen itself ◦ Its reemergence may be a result of changing conditions or old prevention regimes that are no longer working. Examples of such diseases are drug-resistant forms of tuberculosis, bacterial pneumonia, and malaria.

enveloped virus

• a virus formed with a nucleic-acid packed capsid surrounded by a lipid layer

biological vector

• an animal (typically an arthropod) that is infected with a pathogen and is capable of transmitting the pathogen from one host to another