Companion Animal Parasitology & Zoonosis Flashcards
What causes disease?
What causes disease?
- Other living things (organisms)
- The surrounding environment
- Genetic issues
Diseases caused by other organisms?
Diseases caused by other organisms?
. Bacteria . Fungi . Parasites . Viruses (but see section on viruses about their being ‘alive’) . Protozoa
All the organisms above are extremely small. They are microscopic which means you need (usually) a microscope to see them.
Bacteria?
Bacteria?
.Bacteria live as single cells which measure no more than a few thousandths of a millimetre long. The singular of ‘bacteria’ is ‘bacterium’.
.A pinhead would be able hold many hundreds of millions of bacterial cells!
Important points about bacteria:
- Bacteria can be helpful to other organisms for example, yoghurt bacteria.
- Others can be extremely harmful to other organisms such as certain E. coli and Staphylococcus species.
Spiral shaped bacteria?
Spiral shaped bacteria?
Are found in water. They have a cell shape that allows movement in water & some have a “tail” to propel the cell through water.
A number of spiral bacteria (Leptospiria) are responsible for Weil’s Disease. In the UK, Weil’s disease is carried usually by wild rats. It is spread in their urine. Taking a dog for a walk along canals & some inner-city river banks can result in infection to your dog and, you.
Bacteria cells?
Bacteria cells?
Each bacterial cell can reproduce into two cells. Two cells then divide into four cells and so on. Some bacteria can reproduce very quickly and this is why hygiene must be strict when dealing with faeces, vomit and food.
Many bacteria are good and they live in the intestines (the gut bacteria) alongside pathogenic bacteria. A healthy gut contains more good bacteria than bad. A dog’s gut bacteria can be ‘topped up’ with live yoghurt and the currently popular Pre- and Pro-biotic drinks.
The Virus?
The Virus?
Many biologists and other scientists are unsure whether to call viruses living things: a virus can only function inside the cell of another organism. It cannot function in any way when out of a living cell. Whatever scientists eventually decide, there can be no doubt that a viral infection is a serious matter. The number of viral diseases is extensive.
The list below shows just a few of the more common ones that affect dogs.
. Kennel Cough
. Distemper
.Canine enteritis -
also caused by a
bacterial infection
What does the virus look like?
What does the virus look like?
Sometime in the 1930’s, the electron microscope was invented and the only way to see a virus is to use an electron microscope. Electron microscopes are either scanning ones (SEM) or transmission ones (TEM).
Only universities, research institutes and the like possess these complex and hazardous pieces of equipment as they require highly qualified people to operate them because of their complex construction and, the harmful radiation which is used to “see” the smallest of objects.
One of the first objects found with an electron microscope was a virus and this find changed the world forever in the understanding of how illness and general disease was caused.
The special property of an electron microscope is that it can ‘see’ objects which are hundreds of thousands of times smaller than the head of a pin.
Virus process?
Virus process?
The virus becomes active only when inside a living cell. A virus needs the genetic material (DNA) of a living cell to function.
It ‘borrows’ the DNA of its host to replicate that can, depending on the virus, cause severe and sometimes fatal illness for the host.
Because of their nature, antibiotics have no effect whatsoever on a virus.
Parasitic infections?
Parasitic infections?
Fungal parasites. It is probably a bit strange to think that mushrooms and a fungal disease called Ringworm are the same type of organism. Mushrooms are a type of fungus. So are toadstools.
Unfortunately, like all the examples of causes of disease there are harmful types of fungi. Such fungi are parasites. A fungus is completely different to any other living thing. A fungal organism secretes digestive substances onto other living surfaces to obtain their nutrition.
Another living surface could be wood. Yet another can be skin and this where the wrongly-named ‘Ringworm’ comes in because this nasty infection of the skin is not a worm (an animal) but a fungus.
Ringworm?
Ringworm?
.Ringworm is highly contagious which means it is easily passed on to another living thing. It is a zoonosis.
.When examining an animal for ringworm, always wear protective gloves. Destroy the gloves after using them.
.Wash your hands and lower arms too after handling such animals so that there is less chance of passing the spores from ringworm (their egg-like parts) to you, another person or, non-human animal. This is disease is highly contagious and a zoonosis because it is caused by a fungus and their spores are ejected into the air.
A woods lamp?
The infection fluoresces apple green under the ultraviolet light from the equipment. A wood’s lamp may not always work in identifying ringworm as not all fungal strains fluoresce and other things may fluoresce giving the wrong diagnosis.
Ringworm?
Ringworm?
Like all fungal organisms, ringworm reproduces by means of spores (a bit like seeds from plants but microscopic in size). You need a microscope to see them. Spores can cause respiratory problems and in some instances, death.
When a fungal organism is ready to spread its spores, it does so from the centre of the main growth area. Because of this, the spores are expelled into the air in a circular fashion around the central growth area. This pattern accounts for the circular appearance of infection and in this case the common name of the organism.
The spore develops and produces more spores. When the spores are ready to be spread, they are ejected (indicated by the arrows) from the location of the original spore’s growth area.
New growth occurs as a circle around the first area of growth. Ringworm will cause the hair to fall out. The reddened area will be very sore too. Signs are lesions, circular area of alopecia, scaling.
Ringworm can be prevented ONLY by following strict hygiene procedures so that it is not transmitted from one animal to another. This includes the human animal and because of this, ringworm is classed as a zoonosis.
Fungi parasite?
Fungi parasite?
There are a number of diseases caused by parasitic fungi. Ringworm is just one example and it is included because it is so easy to pass it on to other animals including humans.
Endoparasites?
Endoparasites?
A lot of parasites which make their home on or in an animal are animals themselves. All such parasites extract nutrients from their host, to feed. They also use their host as a home, a place to breed and as a way of moving large distances to get to new hosts.
.Remember, an animal who has been abandoned is more likely to be infested with parasites.
.Wear protective gloves to prevent infection to yourself.
.Throw away the gloves after using them.
.Wash your hands and lower arms too after handling such animals so that there is less chance of passing eggs and other parts of parasites to another living thing.
Remember the WHO 6-step hand-washing technique ref: Principles of infection control for animal nursing assistants.
The Tapeworm?
The Tapeworm?
Endoparasite (intestinal). A tapeworm has a tape-like appearance. They have a flattened “body” composed of segments. Each segment can break off from the main body of the parasite and form new tapeworms from eggs the segments contain.
The segments look like grains of rice. They will appear at the anus and in faeces.
The generic name of some tapeworms is Taenia.
(b) Segments of tapeworm.
The segments look like grains of rice. They will appear at the anus and in faeces. A match stick is shown for size comparison.
The generic name of some tapeworms is Taenia.
Roundworms?
Roundworms?
Are found in other animals are easily passed to humans. Some people can be greatly harmed by certain roundworm species and the host animal suffers too. Pups and kittens suffer poor growth and adult animals suffer discomfort, loss of appetite and in extreme, neglected cases, death.
Example of nematodes are Toxocara cati and Toxocara leonina.
Internal parasite signs?
Internal parasite signs?
Examples are:
.Worms and/or eggs around anus and in faeces.
.Polyphagia; a distended abdomen
.Weight loss
.Coughing and vomiting.
.Whole endoparasites can be vomited and this would indicate a severe infestation of the organism.
.Tapeworm “eggs” can be seen around the anus and in faeces and roundworms (complete ones) can be seen in faeces too.
.Some roundworms are a serious threat to humans.
