Non-Human Viral Infections

drugs that mimic the building blocks of DNA so that the drugs are incorporated into the genome by mistake. This halts the viral life cycle. The backbone of DNA is broken, stopping the growth of viral DNA. An example of this type of antiviral drug is acyclovir, used for herpesvirus infections. For HIV, there are protease inhibitors that block the enzyme HIV-1 protease, necessary for the HIV replication cycle.

NON-HUMAN VIRAL INFECTIONS

Viruses infect all types of cells in the world, including plants, other animals, archaea, and bacteria. Remember that viruses are relatively specific to a particular species and that some viruses, called satellite viruses, can only infect cells infected already by other viruses.

Viruses can infect many different common animals, including livestock, horses, dogs, and cats—many of which are vaccinated as some are serious. Even insects can become infected with viruses, which have affected populations of bees.

Plants are also highly susceptible to viruses. These are transported via vectors, which is also how many animal and human diseases get spread. Vectors are carrier organisms that carry the virus from organism to organism without getting sick themselves. Insects, some worms, single-celled organisms, and some fungal organisms have been found to be vectors. Efforts to decrease the numbers of vectors are ways to decrease plant virus infections.

Plants can defend against viral diseases by making resistance genes or R genes. R genes trigger areas of cell death around the infection in order to limit the spread of virus particles in the plant. It causes dark spots on infected plants. There are natural antiviral disinfectants also produced by infected plants, such as salicylic acid, reactive oxygen species, and nitric oxide.

The bacteriophage is a virus that only infects bacteria. There are 250 million bacteriophages per milliliter of seawater, making it the most abundant biological species in watery environments. These viruses bind to surface receptor molecules on the bacterium, injecting the viral genome into the bacterial cell. This triggers bacterial polymerase to translate viral messenger RNA into proteins that become new viral

particles or that help in the assembly of virus particles. There are viral enzymes that break down the bacterial cell membrane. This is a fast process, killing the bacterium within minutes, releasing new bacteriophages.

Bacteria defend themselves from viral particles by making restriction endonucleases, which are enzymes that cut up the viral DNA because it is foreign to the cell. Bacteria also have the ability to have acquired immunity to the virus particles by retaining fragments of the viral genomes within the cell.

The place in the ecosystem that has the most viral particles is seawater. Most are bacteriophages that infect the different bacterial species in the oceans. These viruses do not infect animals or plants and are necessary parts of the ocean ecosystem. They also kill off cyanobacteria and phytoplankton in the oceans, being an important part of the ocean food chain. They kill off bacteria that stimulate the growth of new organisms in the ocean, particularly phytoplankton. Viruses kill 20 percent of the ocean’s biomass every day with 10 times the viruses in the ocean as compared to archaea and bacteria.