There are prophage genes that lysogenicbacterial cells carry.
The presence of a prophage can cause a cell to make a toxin.
If the Page 358 bacterium that causes strep throat carries a prophage that causes a red skin rash, then it will cause scarlet fever, which is named because the toxin causes a widespread red skin rash as it spreads through the body.
The cause of diphtheria is caused by a bacterium.
The lining of the upper respiratory tract is damaged by the diphtheria toxin.
Different animal viruses have different ways of introducing their genetic material into their host cells.
The process of attachment and fusion of the envelope with the host cell is as simple as it gets.
Endocytosis is the process of taking nude and nude viruses into host cells.
The capsid and envelope are removed if necessary after the virus enters.
The viral genome is no longer covered and the virus can enter the lysogenic cycle.
The rapid and severe destruction of host cells is caused by Viruses that enter directly into the lytic cycle.
50% of people die from the disease within 2-21 days of being exposed to it.
HIV enters first into the lysogenic cycle and can be inactive for many years before AIDS symptoms emerge.
The penetration for animal viruses is variable.
Some mature viruses are released.
Some animal viruses take envelopes from other parts of the cell, such as the nuclear envelope or Golgi apparatus.
Host celllysis releases naked animal viruses.
Figure 20.3 shows the reproduction of HIV.
HIV uses reverse transcription and double-stranded DNA to make a copy of the genes in the cell.
It is unique to retroviruses.
Before a retroviruses can integrate into the host's genome, or use the host cell's machinery to translate its proteins, it must first convert its RNA to DNA.
The reverse transcriptase is able to synthesise from itsRNA genome a single DNA strand, called cDNA, which is a complement to the viral RNA.
The single strand of cDNA is used as a template.
The double-stranded virus DNA is integrated into the host genome.
When host DNA is replicated, the viral DNA remains in the host genome.
In the case of HIV, the new viruses are produced by the steps already cited: biosynthesis, maturation, and release.
HIV can remain undetected for a long time.
The median survival time after HIV is 9-11 years without treatment.
The emergence of AIDS can be delayed by treatment with antiretroviral drugs, which interfere with one or more of the steps of HIV reproduction.
One type of antiretroviral drug, AZT, consists of reverse transcriptase inhibitors, which bind to reverse transcriptase and interfere with its function.
Acyclovir is a drug that is used to treat a variety of diseases.
It is difficult to find a cure for HIV, which is a rapidly evolving virus.
HIV is engaged in an "arms race" with an animal's immune system.
Although a new drug or vaccine may work against some, it is very likely that one type within the billions of virus copies will evolve resistance and continue the infection.
There is no cure for HIV because of the rapid evolution of resistance.
Emerging diseases are caused by viruses that are able to cause large numbers of humans to get sick.
There are several types of events that can cause a viral disease to arise and cause a widespread human illness.
There are emerging diseases.
Emerging diseases are new or have increased prevalence.
The agents may have acquired new virulence factors or the environment may have encouraged their spread.
West Africa and Southeast Asia were the only places where the virus was found before 2007.
There was an outbreak in Brazil in 2015.
An individual with the strain from Southeast Asia was brought to the region.
The outbreak was caused by a suitable environment that included high populations of mosquitoes and a susceptible human population.
This outbreak could spread across the Americas, including the United States, as was discussed in the Biological Systems feature.
The H spike allows the virus to bind to itsreceptor, and the N spike allows mature viruses to exit the cell.
There are at least 16 types of H and 9 types of N spikes.
The type of spike is what determines the codes assigned to the flu viruses.
The H5N1 virus has a variety of H5 spikes and N1 spikes.