biology zoology blog benno meyer pandemic

Also a Pandemic

But who cares?

There are times when everyone is talking about ‘pandemics’ and it is, of course, something to worry and to take action about. But there are not only pandemics that affect human health directly, but pandemics amongst animals that can not only be devastating for the animals themselves but indirectly for humans as well. For instance, the so-called African swine fever, a terrible and frighteningly contagious viral disease of pigs that is killing domestic and wild pigs around the world. Although it has not yet reached North America it is estimated that in 2019 alone 300 million pigs had to be killed or died in China and that by now the disease has spread to 50 countries. Affected pigs (and no age group is spared) develop a high fever, lose their appetite and can die within a week after being infected. Humans can’t catch the disease, but can transmit it to other still healthy pigs. The foot-and-mouth disease is another livestock disease caused by a virus and affects all species with cloven hoofs. The disease spreads very easily and although lethal in adult animals only to about 5%, it can have a severe effect on the health of calves, lambs, and piglets killing 20% of those that are still receiving milk containing the FMD-virus from their sick mothers. That birds, too, can be sick and their illness can reach the level of a pandemic, we know from the bird flu that started in Hong Kong in 1997 and then arrived in Europe in 2004 where it lead to the controlled killing of millions of domestic chickens, ducks, and geese.

However, one ‘silent’ pandemic that few know about (and can pronounce correctly) is the chytridiomycosis disease of amphibians. This disease, caused not by a virus but an aquatic fungus by the name of Batrachochytrium dendrobatidis is decimating frogs, toads, and B. salamandrivorans newts and salamanders worldwide. And there is little one can do about it. The disease is thought to have originally come from fire belly toads in South Korea, which via the pet trade made it to other countries. The Korean fire belly toads may perhaps have been more resistant to the fungus, but elsewhere in the world all amphibian species were and still are at risk. Tadpoles and aquatic larval amphibians seem more resistant, but as they metamorphose and turn into a terrestrial animal, symptoms appear. The infected animal may not die immediately but can live quite a while with the disease and transmit it to other individuals upon close contact. Since the fungus colonizes the skin of its victim and amphibians use their skin for respiration, an infected individual begins to suffer. The fungus will also affect the nervous system, making the victim appear sluggish and losing its appetite. The skin may be discoloured or peeling and the position, especially that of the hind legs, would be unnatural. Ultimately the sick individual would become anorexic and lethargic, the pupils of the eye would become constricted, blood vessels in the extremities would contain more blood and the animal would succumb to the disease.

What can be done to fight the disease? As with other pandemic diseases isolation of sick individuals and “social distancing” are the methods of choice. And while this may be possible to achieve with captive amphibians it is virtually impossible to apply to wild living individuals. The disease-causing fungus is unusual in that it possesses spores that swim in the water, propelling themselves with a single and long whiplash flagellum. They share this mode of reproduction with another water mould known as Saprolegnia that can also attack weak or injured amphibians and fish, especially their unfertilized eggs. But do people care? After all, amphibians are not exactly human’s “best friends”. They do, however, play important roles in Nature, they have been around for about 360 million years and there are enthusiasts like myself who love these cold-blooded creatures with pretty eyes and a constant smile on their face.

© Dr V.B. Meyer-Rochow and, 2020.
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