Ranavirus

Ranavirus is a group of viruses that belong to a family called Iridoviridae. This family has several types of viruses, but Ranavirus is special because it can make amphibians and reptiles sick. Amphibians include animals like frogs and salamanders.

Besides affecting amphibians and reptiles, Ranavirus is also one of three types in this virus family that can infect teleost fishes. The other two types that can infect fish are called Lymphocystivirus and Megalocytivirus. These viruses are important to study because they can cause diseases in many aquatic animals, affecting wildlife and pet owners alike.

Ecological impact

Ranaviruses are a group of viruses that can cause serious infections in many types of fish, both in the wild and in farms. These infections can lead to significant losses in fish populations, which is important for the fishing industry.

Unlike some similar viruses, Ranaviruses have also been linked to the decline of amphibian populations around the world. Their effect on amphibians has been compared to a harmful fungus that causes a disease in these animals. Studies show that Ranavirus outbreaks happen worldwide, but they are reported more often in some places than others, suggesting that more monitoring is needed in certain regions.

Etymology

The word "Rana" comes from the Latin word for "frog". This name was chosen because the first time scientists found a Ranavirus, it was in the 1960s inside a Northern leopard frog (Lithobates pipiens).

Evolution

Ranaviruses seem to have developed from a virus that originally affected fish. Over time, this virus began to infect amphibians and reptiles as well.

Hosts

Ranavirus can affect many kinds of animals, especially frogs and some turtles and lizards. Some frogs that can get sick include wood frogs, American bullfrogs, and pickerel frogs. There are also some endangered frog species that can be affected.

Some reptiles that can get this virus include green pythons, different kinds of tortoises such as Burmese star tortoises and leopard tortoises, and various lizards and turtles like the mountain lizard and red-eared sliders.

Taxonomy

The genus Ranavirus includes several different viruses, each named after the animals they affect. Some examples are Common midwife toad virus-E and Frog virus 3.

The family Iridoviridae has seven groups of viruses, and Ranavirus is one of them. Ranavirus can infect frogs, salamanders, and some fish, along with two other groups called Lymphocystivirus and Megalocytivirus.

Structure

Ranaviruses are big viruses shaped like balls, with a size of about 150 nanometers across. They contain DNA, a type of genetic material, that has instructions for making around 100 different parts of the virus. The outer shell of these viruses is mainly made of a special protein called the major capsid protein.

Replication

Ranaviruses, like Frog virus 3, can live and grow in host cells between 12 and 32 degrees Celsius. They enter cells by attaching to special receptors and moving inside. Once inside, the virus removes its coat and moves into the cell’s control center, called the nucleus, where it starts copying its genetic material using a special enzyme. The virus then moves this genetic material to another part of the cell to continue copying, eventually forming long strands of DNA. These strands are then packed into new virus particles that can infect other cells. The virus’s genetic material is circular and has extra pieces of DNA at the ends.

DNA repair

A type of ranavirus found in Chinese giant salamanders produces a protein that helps repair DNA damage in cells by bringing broken pieces back together.

Transmission

Ranaviruses can spread in many ways, such as through dirty soil, touching infected animals, being in water with the virus, or eating infected tissue when animals hunt, scavenge, or eat each other. These viruses can stay alive in water for many weeks, even without an animal host.

Epizoology

Ranaviruses have caused many frogs and other amphibians to get very sick and die in places like Asia, Europe, North America, and South America. Scientists have found these viruses in wild amphibians in Australia too, but they haven't caused big groups of animals to die there.

Pathogenesis

When a virus enters a cell, it starts making its proteins quickly. This can cause the cell to break down or stop working properly within just a few hours.

Seasonal disease dynamics

Scientists have noticed that some diseases caused by Ranavirus happen more often in certain seasons. These viruses grow best between 8-30 °C, and they tend to grow faster when it’s warmer. This, along with changes in young frogs’ ability to fight off infections, leads to more disease cases in the warm summer months.

Young frogs, especially when they are getting ready to change into adults, have weaker immune systems. This makes them more vulnerable to the virus. Because of this, many cases of disease in frogs in the United States happen between June and August.

Environmental persistence

We don't know much about how long ranaviruses can survive in nature. In normal outdoor conditions, a certain type of ranavirus can last about one day. How long the virus stays around probably depends on things like temperature and tiny living things in the water.

Scientists have looked for places where the virus might hide, which could help explain how it stays in amphibian groups. Some frogs or salamanders that don't get very sick from the virus might carry it and spread it to younger animals. Because ranaviruses can infect many different animals, fish and reptiles might also help the virus survive. Studies have shown that the virus can move between different kinds of animals.

Gross pathology

When animals get sick from Ranavirus, they can show signs like redness, swelling all over their bodies, bleeding under the skin, swollen limbs, and livers that look puffy and fragile.