What is Virus?

A virus (from the Latin virus meaning toxin or poison) is a small infectious agent that can replicate only inside the living cells of other organisms. Most viruses are too small to be seen directly with a light microscope. Viruses infect all types of organisms, from animals and plants to bacteria and archaea. Viruses vary from simple helical and icosahedral shapes to more complex structures. Most viruses are about one hundred times smaller than an average bacterium. In evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity.

Viruses spread in many ways; plant viruses are often transmitted from plant to plant by insects that feed on sap, such as aphids, while animal viruses can be carried by blood-sucking insects. Influenza viruses are spread by coughing and sneezing. HIV is one of several viruses transmitted through sexual contact and by exposure to infected blood. Viruses can infect only a limited range of host cells called the "host range". Viral infections in animals provoke an immune response that usually eliminates the infecting virus. Microorganisms also have defences against viral infection, such as restriction modification systems which restrict the growth of viruses.

Viruses display a wide diversity of shapes and sizes, called morphologies. Generally viruses are much smaller than bacteria. Most viruses that have been studied have a diameter between 10 and 300 nanometres. To increase the contrast between viruses and the background, electron-dense "stains" are used. When virions are coated with stain (positive staining), fine detail is obscured. A complete virus particle, known as a virion, consists of nucleic acid surrounded by a protective coat of protein called a capsid. Viruses can have a lipid "envelope" derived from the host cell membrane.

Virally coded protein subunits will self-assemble to form a capsid, generally requiring the presence of the virus genome. Complex viruses code for proteins that assist in the construction of their capsid. Proteins associated with nucleic acid are known as nucleoproteins, and the association of viral capsid proteins with viral nucleic acid is called a nucleocapsid. The capsid and entire virus structure can be mechanically (physically) probed through atomic force microscopy

Swine influenza

Swine influenza (also called swine flu, hog flu, pig flu and sometimes, the swine) is an infection by any one of several types of swine influenza virus. Swine influenza virus (SIV) is any strain of the influenza family of viruses that is endemic in pigs. As of 2009, the known SIV strains include influenza C and the subtypes of influenza A known as H1N1, H1N2, H3N1, H3N2, and H2N3.

Swine influenza virus is common throughout pig populations worldwide. Transmission of the virus from pigs to humans is not common and does not always lead to human influenza, often resulting only in the production of antibodies in the blood. If transmission does cause human influenza, it is called zoonotic swine flu. People with regular exposure to pigs are at increased risk of swine flu infection. The meat of an infected animal poses no risk of infection when properly cooked.

Swine influenza was first proposed to be a disease related to human influenza during the 1918 flu pandemic, when pigs became sick at the same time as humans. The first identification of an influenza virus as a cause of disease in pigs occurred about ten years later, in 1930. For the following 60 years, swine influenza strains were almost exclusively H1N1. Then, between 1997 and 2002, new strains of three different subtypes and five different genotypes emerged as causes of influenza among pigs in North America. In 1997–1998, H3N2 strains emerged. These strains, which include genes derived by reassortment from human, swine and avian viruses, have become a major cause of swine influenza in North America. Reassortment between H1N1 and H3N2 produced H1N2. In 1999 in Canada, a strain of H4N6 crossed the species barrier from birds to pigs, but was contained on a single farm.

The H1N1 form of swine flu is one of the descendants of the strain that caused the 1918 flu pandemic. As well as persisting in pigs, the descendants of the 1918 virus have also circulated in humans through the 20th century, contributing to the normal seasonal epidemics of influenza. However, direct transmission from pigs to humans is rare, with only 12 cases in the U.S. since 2005. Nevertheless, the retention of influenza strains in pigs after these strains have disappeared from the human population might make pigs a reservoir where influenza viruses could persist, later emerging to reinfect humans once human immunity to these strains has waned.

Reference : Wikipedia.org

Bear

American Black Bear

These bears are often found in national parks, where they raid campsites for food. They have a keen sense of smell, and usually hunt at night. They are smaller and less dangerous than their brown bear cousins.

Asiatic Black Bear

This bear has a broader face than the American black bear and a v-shaped patch of white fur on its chest. They are very good climbers and often climb up trees to catch insect or to reach fruit and honey.

Grizzly Bear

The grizzly bear is one of the largest brown bears in the world. Other members of the brown bear family include the Alaskan brown bear, the American brown bear, and the brown bears of Europe and Asia. Grizzlies can stand more than 10 ft. high on their hind legs. These animals mainly live in forests, and will eat almost anything including fruit, deer, and fish, and have even been witnessed killing other bears.

Polar Bear

The polar bear is the world''s largest bear. Females can weigh over 650 lbs, while males can weigh more than double that weight. Polar bears are great swimmers, they have been seen in open waters hundreds of miles from the land. Males are active year round, while females usually hibernate in ice dens during the winter. A female polar bear will give birth to their young inside of these ice dens, and then emerge in the spring.

Sun Bear

The sun bear is one of the smallest and most intelligent bears in the world. They live in the tropical forests of Southeast Asia, and feed on fruit and a variety of animals. Sun bears sleep during the day in nests they make out of leafy branches. The spend the nights foraging for food.

Sloth Bear

The sloth bear has quite an unusual diet they fed on termites by, sucking them up like a vacuum. Sloths have very powerful feet and long claws.

Spectacled Bear

The spectacled bear is the only bear found in South America. This bear''s fur is mostly black or brown with white spectacles. They are great climbers, and live in warm climates where they don''t need to hibernate.