CASUAL BROWSERS - basic background information
The diseases we work on are caused by bacteria (similar to E. coli) or much larger, more advanced organisms called protozoa (like amoeba or the agent that causes malaria).
They are all transmitted by biting arthropods (ticks, fleas or flies).
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A tick (Ixodes ricinus) attached to the skin of a dog. |
The mouthparts of a tick which are adapted for puncturing and adhering to skin. |
Babesiosis
Babesiosis is a tick-borne disease of companion animals, humans and food animals of worldwide significance. The disease is caused by protozoan organisms of the genus Babesia (sometimes called "piroplasms" due to their pear-like shape when seen within red blood cells). Of particular significance to us are the species B. canis and B.gibsoni, which can infect dogs, and B. felis, B. cati and B. pantherae which are found in cats.
The Babesias are protozoans, somewhat similar to those causing malaria and sleeping sickness. They have a complex two-host life cycle whereby they reproduce sexually in their tick host and asexually in mammals. The organisms replicate inside host red blood cells and cause a spectrum of disease ranging from no symptoms to a fulminant, acute disease, which may be fatal. Disease symptoms are usually due to the widespread destruction of red-blood cells with the concomitant release of haemoglobin and organisms into the blood stream. The major symptoms are fever, anaemia, haemoglobinuria (dark red, haemoglobin-containing urine), jaundice, lethargy and, in severe cases, acute collapse with multiple organ failure.
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A urinary catheter is in place which is collecting clearly red urine. He recovered after several days in intensive care. |
Bartonellosis
Bacteria of the genus Bartonella are found in the blood of many wild rodents and larger mammals, such as deer, throughout the world. In these natural hosts, infection with the bacteria does not appear to influence fitness. However, the transfer of these bacteria to domestic animals and humans can result in disease.
Bartonella appear to be transmitted from one animal to another by a range of biting insects, particularly fleas, although ticks have also been implicated. The disease can also pass, to humans at least, by direct inoculation e.g. by scratching or biting by heavily infected animals (thus giving rise to "cat scratch disease" a problem in immuno-compromised humans).
Bartonellosis (infection with Bartonella) is largely an infection of cats where it causes a wide spectrum of problems dependent on the underlying health of the animal, although current work is investigating its association with disease in other companion animal species. It appears that many animals carry Bartonella but remain symptomless. When stressed or immuno-compromised cats may develop fever, anaemia, heart and liver problems and neurological signs.
Borreliosis
Borreliosis (sometimes known as Lyme disease) is caused by bacteria called Borrelia. Several species of this organism exist in Europe and all cause disease when transmitted to dogs and humans (and, less commonly, to cats, and horses). These organisms are adapted to live in rodent and wildlife reservoirs in which they cause no apparent problems. When ticks which harbour the organisms bite an animal, the bacteria are transmitted into the host with tick saliva and multiply in the bloodstream.
It appears that only certain types of ticks (known as Ixodes) can transmit Borrelia. Unfortunately the most common UK tick, the sheep tick (Ixodes ricinus), is one of these.
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A dog with borreliosis, the dog is lethargic, has a fever and has pronounced lameness in its right foreleg. |
The point of tick-attachment with the spreading |
In humans the typical disease progression is a red rash around the tick bite which resolves and is followed by flu-like symptoms and arthritis. In animals the rash is not usually observed and the first signs of illness are that the animal appears "off-colour"; this lethargy and anorexia is often accompanied by lameness due to arthritic changes in the joints.
The infection is managed with antibiotic therapy but prevention is better than cure - evidence suggests that the ticks do not infect their host for 24 to 72 hours post-attachment. Removal of the ticks in this time frame should forestall the disease as would use of an effective acaricide (i.e. tick-killing preparation).
Ehrlichiosis
Ehrlichiosis is caused by a small bacterium (a rickettsia) from the genus Ehrlichia. These bacteria are predominantly passed from animal to animal by ticks in a similar manner to the transmission of Lyme disease. Once in the bloodstream the bacteria invade white blood cells (or platelets) where they multiply.
The clinical manifestations of ehrlichiosis are very varied, ranging from general loss of condition with intermittent fever to more organ specific pathology such as arthritis or eye problems. There are two major types of Ehrlichia which differ in the type of white blood cells they infect. The monocytic Ehrlichia (generally E. canis) tends to give rise to a chronic disease, whereas the granulocytic Ehrlichia (E. phagocytophila) causes a much more acute disease with high temperatures, anorexia and reluctance to move in infected animals. Both types cause depletion of clotting factors in the blood resulting in severe haemorrhage in some cases.
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Purple-stained white blood cells (monocytes) in this case infected with Ehrlichia canis; buffy coat smear |
A dog with ehrlichiosis and haemorrhage in the eye. This a common problem reflecting the damage the disease does to the body’s blood clotting mechanisms. |
Leishmaniasis
Leishmaniasis is a disease caused by protozoans of the genus Leishmania, and is transmitted by biting sandflies. Once in the body the organism lives inside macrophages, cells of the immune system. The disease is a major human health problem in parts of Africa, The Middle-East, South America and is widespread in the Mediterranean basin. The disease is a bigger problem in dogs than cats and a lot of work is being carried out to see if dogs are a natural reservoir of the disease in some areas.
Dogs infected with Leishmania tend to develop a chronic, systemic disease with a variable course of development. The commonest symptoms are weight loss and lack of endurance, lymphadenomegaly ("swollen glands") and skin disease, particularly around the eyes. If caught in the early stages the disease can be successfully controlled by chemotherapy, but the organism is good at hiding and so repeated courses of therapy may be necessary throughout the animal’s life.
This dog has typical signs of
leishmaniasis,
with scaling skin and
alopecia around the
nose and eyes.
Treatment/Diagnosis/Vaccination
More information on these aspects of the diseases can be found in the more specialist vet's section.
See also "Taking your pet abroad for holidays"