Bacteria, Virus, Fungus and Protozoa

Carol Raczykowski
Reviewed by Dr. William Holleman

(Reprinted from Pygmy Goat WORLD magazine with permission)

Have your eyes ever glassed over as your veterinarian began to explain about the latest malady your goat has come down with? What was he saying? Something about a virus or bacteria. Oh well, it doesn't make any difference. Or does it?

Knowing the difference between different forms of illness may be one of the first steps in knowing how to deal with the problem. For example, if your goat has a virus, you can usually assume that it will not respond to antibiotics. Or, knowing that Leptospirosis is a bacterian rather than a protozoan will help you decide on appropriate treatment. All have different properties and respond differently to drugs.

When treating livestock it is always best to use the rifle approach rather than the shotgun. Find out what your goat has so you can treat it with a single appropriate treatment (rifle), rather than throwing a bunch of different treatments (shotgun) at your goat, none of which may work.

Understanding the enemy is always helpful. Bacteria are living things. They can reproduce all by themselves and do not need a host to survive. They are single-celled and reproduce by duplicating themselves. Bacteria are responsive to antibiotics. Tetanus and most forms of pneumonia are some of the bacterial diseases in goats. 

A virus is smaller than one cell. It lives within a cell (intracellular) to survive and derives its ability to multiply from its host cell. It is not responsive to antibiotics. A virus is not a living thing so antibiotics, intended to kill living things, are not effective. A virus cannot multiply outside a living host cell. There is no treatment for a virus, just supportive therapy. The body will fight off most viruses over the course of time. Vaccines do not cure viruses, so the only way to protect your goat from viruses is through specific vaccines. Vaccines help the animal to build antibodies against the virus. There are not vaccines for every virus. Bluetongue and adenovirus are examples of viral disease. 

Fungus is a saprophytic organism. It can live by itself and does not need a host to survive. A fungus can be sexual or asexual (vegetative). It can reproduce on its own, outside the host's body, but once it is inside the host (ingested, etc.) it turns to sexual reproduction and depends upon its host.

Fungi do not respond to antibiotics in the true sense. They respond to a fungicide. Ringworm is a good example. Fungal pneumonia is an internal illness that we are all exposed to. Before the fungus is inhaled, it is an external fungus which reproduces on its own. After it is inhaled and takes hold, it begins to reproduce sexually and relies on its host. Each day we inhale a multitude of harmful fungi. Our body throws most of these fungus off. But, if our immune system has been compromised in some way by stress or other factors, we are much more susceptible.

Protozoans are living, one-celled creatures that can live inside or outside the cell. Most antibiotics, such as penicillin, don't work on protozoan diseases. However, they are susceptible to some antibiotics such as sulfas *sulfonamides*. Coccidiosis is caused by protozoans; a coccidia lives inside the cell and reproduces there until it ruptures the cell wall and releases the oocysts. Cryptosporidiosis & Leptospirosis are also protozoan diseases in goats.

Although these explanations are simplistic, they are intended to give you a clear picture of why it is so important to know which disease organism you are faced with. Treatment appropriate for one type of illness will not work at all on another. That's where your veterinarian is essential. Don't try the shotgun approach with your goats by treating them with what you think may work and then call your vet when it doesn't. By then, the disease process may be too advanced. If it is too late and your goat dies, have a necropsy done.

The following note was sent to the  Reader's Forum in the next issue of Goat WORLD:

Dear Goat WORLD,

I thought the article on the differences in bacteria, virus, fungus and protozoans was very good, although I do have a difference of opinion on some of the definitions. The bacteria have more plant-like characteristics while the protozoans more animal-like. Many believe that a virus is living and can be defined as strands of nuclear material surrounded by a protein coat. Chlamydia and rickettsia (both causes of severe disease in goats) are classified somewhere between bacteria and viruses. - Dr. Kay Orlando, DVM

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