By Dr Steve Surujbally
General considerations
Diseases can be caused by viruses, bacteria, one-celled animal organisms (protozoa) and fungi.
Viruses are truly interesting. For one thing, they can only multiply in living cells of the host. This means that their structure can be very simple, since they rely solely on the metabolic processes of the host. I used the word ‘multiply’ and not ‘reproduce.’ ‘Reproduce’ means that the same living cell will split into many using its own energy, or two living cells will come together and produce offspring. The virus, however, has to attach itself to other living cells, then enter these living cells, then divert and disrupt the normal cell chemistry of the invaded cell in such a way as to produce new viral material. This new material then assembles itself and can then leave the cell as several new viruses, which are ready to this waylay new uninfected host cells – and this activity is repeated and repeated. There are those who argue that viruses are simply a package of molecules, and since they can’t reproduce on their own (a characteristic of living things) they should not be considered live organisms.
Viruses in the animal would vary considerably in size. The canine parvovirus and the foot-and-mouth disease virus are very tiny (one-ten thousandth of a millimetre) when compared with say the pox viruses or the herpes virus (the latter can be 18-20 times larger than the canine parvovirus).
Some viruses are very infectious (easily transmissible) and very pathogenic (causing quick death). Other viruses are ‘slow acting’ and do not cause overt disease for months or even years after they have infected the host. The scrapie organism which has recently been implicated in mad cow disease is one such example.
Bacteria (also called germs, microbes, micro-organisms) though microscopic, are much larger than viruses and are actually living cells. They are the lowest form of plant life. They come in various shapes. Sometimes the type of shape gives the bacteria a name. For example, a single spherical bacteria is known as ‘coccus.’ If there is a chain of these bacteria, then they are called ‘streptococcus.’ ‘Staphylococcus’ is the name given to bacteria which bunch together like grapes, and so on.
The reproduction of bacteria is an interesting consideration.
The simplicity of multiplication (just by dividing itself and forming two new bacteria which can further divide themselves and so on) and the speed of division may result in the formation of millions of bacteria from a single cell within 24 hours. Of course, bacteria can only multiply if the conditions are right (eg warmth, moisture). All these facts should be borne in mind when we begin to discuss treatment regimes with antibiotics.
Some bacteria (spores) can actually protect themselves against an inclement environment by developing protective coatings. Good examples are the anthrax and the tetanus (‘lockjaw’) germs. Such infectious agents are capable of surviving (in the soil) for years outside the host animal’s body.
Although bacteria are larger than viruses, they are still too small to see with the naked eye. A drop of water may contain hundreds of bacteria. Some bacteria can actually move of their own accord. This means they can search and find a host which will allow their survival.
Protozoa are microscopic one-celled animals which can invade the pet’s body. They are parasites and can cause serious ailments like amoebic dysentery, tick-borne diseases and malaria (in humans).
Fungi (singular: fungus) are plant organisms which live usually on decaying and dead animal/vegetable matter (often in the soil). This soil reservoir serves as the primary source of many infections. The infection is acquired by inhalation, ingestion or traumatic (physical) introduction of spores produced by the fungus. Some fungi are opportunistic. This means that they can only cause damage in the host, if the latter is already debilitated. For example, if the potential host has undergone stresses like captivity, malnutrition, cancer, etc, such an animal is much more vulnerable to fungal infection. Lastly, and of import, is the fact that once certain obstinate fungi have attached themselves to the host, they are difficult to eliminate and no available chemotherapeutic agent (drug) consistently gives satisfactory results.
Next week we will deal with the methods that those micro-organisms use to enter the host’s body.
Until then, have a pleasant and peaceful week.
Please implement disease preventative measures (vaccinations, routine dewormings, monthly anti-heartworm medication, etc) and adopt-a-pet from the GSPCA’s Animal Clinic and Shelter at Robb Street and Orange Walk, if you have the wherewithal to care well for the animals. Do not stray your unwanted pets, take them to the GSPCA’s Clinic and Shelter instead. If you see anyone being cruel to an animal, or if you need any technical information, please get in touch with the Clinic and Shelter by calling 226-4237.
