Toxoplasmosis in the Red Fox Population(Vulpes vulpes)
Updated: Nov 20, 2020
Toxoplasmosis: Is a Parasitic Disease caused by the Protozoan Toxoplasmosis gondi. Protozoan being a single-celled microscopic animal. The disease can be found in almost all warm blooded birds and animals, but the only animal that Toxoplasmosis oocysts (A cyst containing a cell) can reproduce is the domestic cat. The oocysts are released in the cat's faeces.
Studies in rats have shown that rats infected with Toxoplasmosis do not fear cat pheromones even though Rodents instinctively shy away from the smells of a cat. So it would seem that for the parasite to complete its life cycle the infected rat would have to be caught by a cat. What better way than to infect the part of the brain that would normally shy away from this and make life harder for the cat to catch the rat! So the cat catches and kills the rat and eats it and the life cycle is complete and ready to start again when the cat goes toilet.
But what happens if it is a fox that catches the rat. It would seem that the Toxoplasmosis goes through the same stages and infects the part of the brain and or another part of the body that goes on then to affect the part of the brain that is usually associated with fear and the fight or flight instinct. Whilst the fox can't pass on this disease, it is left with the condition none the less. However some foxes in good health and with a good immune system can fight this successfully.
There are several ways that foxes and a host of other mammals and birds can catch toxoplasmosis, including humans. Toxoplasmosis can be caught by direct contact with the oocysts that are able to survive in the environment for a year and more.
Humans can catch this from not washing their hands correctly after cleaning out a cat litter tray or when gardening they may come into contact with the oocysts. Not washing garden produce correctly could lead to digestion of the oocysts. Eating under cooked meats that contain Toxoplasmosis cysts is another source of infection. Toxoplasmosis can also be passed from mothers to unborn babies.
So looking directly at the possible routes of infection for the red fox population it is clear to see there are several ways a fox can become infected. Whilst an infected cat will usually only shed the oocysts for two weeks, during this time Millions could be in the environment.
Oocysts take between 1-5 days to sporulate in the environment and become infective. These oocysts transform into tachyzoites shortly after ingestion. These tachyzoites localize in neural and muscle tissue and develop into tissue cyst bradyzoites. Tachyzoite[tak′i-zō′īt] Definitions. A rapidly multiplying stage in the development of the tissue phase of certain coccidial infections, as in Toxoplasma gondii development in acute infections of toxoplasmosis. Tachy in Latin translates as rapid.
bra·dy·zo·ite (brad'ē-zō'īt) A slowly multiplying encysted form of sporozoan parasite typical of chronic infection with Toxoplasma gondii. It has also been called a merozoite or zoite; the complex of bradyzoites within an enclosing membrane has also been called
a pseudocyst, though it is now regarded as a true cyst. Brady in Latin translates as slow.
Cats usually bury their toilet and foxes will bury any surplus food, only to return to the larder when food may be in short supply. This one aspect of both cat and fox behaviour could lead to infection for the fox. Foxes will also predate rats and mice and will scavenge
dead cats bodies, another possible source of infection! As a vixen could infect her unborn cubs if she was suffering from Toxo, this too is a source of infection that needs to be considered.
Symptoms we have noticed in Toxo positive foxes are as follows: No fear and no real signs of aggression, circling, head pressing, food dangling from the foxes mouth whilst the fox seems completely unaware of this. Walking up to an object and then just standing there, seemingly unaware of the fact that if it moved to the left or right it could pass the object in the way. Following feet but unaware of things going on above knee level, teeth grinding and in extreme cases fitting. we have also seen a number of foxes that tend to bloat up to 2 to 3 times their natural weight. Several foxes that have bloated have left vets scratching their heads as to why.
With all the Toxo infected foxes we have dealt with over the years the condition left them almost like a domestic dog. Whilst this may be difficult to understand for anyone not involved with fox rescue, we have found in almost all cases of Toxo infection, the wild eyes that you would expect to see in a fox are gone and it is almost like looking into a domestic dogs eyes where Toxoplasmosis is involved. We have also found for whatever reason, the toxo foxes always seem to have longer than you would expect to see toe nails.
Determining Toxoplasmosis: Whilst signs and behaviour traits may give an insight as to whether a fox is suffering from this condition, to be sure, blood tests need to be done specifically for Toxoplasmosis, as even normal bloods will show up no real abnormalities.
The blood test is done and if a toxo count is present another test needs to be done two weeks later. The reason for this is to see as to whether the count has gone down, stabilised or is rising. If the count has gone down or stabilised it means the condition has been successfully treated. If it has risen obviously the opposite is true, the infection is active. The Toxoplasmosis blood test will usually give an indication to Past/Recent Exposure, Active Exposure, or No Exposure and this is done by testing the IgG and IgM levels. What can be even more confusing is that Toxoplasmosis can go into a dormant stage only to reactivate weeks, months and possibly even years later when the host becomes for whatever reason immune suppressed.
Treatment: Along with a good diet, Antirobe is used to treat active Toxoplasmosis and whilst the treatment is said to be successful, any brain damage can't be reversed and the vast majority of the foxes we deal with suffering from Toxoplasmosis are usually recent/past exposure and Antirobe (Clindamycin) seems to have no effect on this.
Locations: For whatever reasons we have found that more Toxoplasmosis positive foxes come from the South of the Country, and Essex / London, at least in the year 2015, seemed to be a hot spot. Further research into Toxoplasmosis by the National Fox Welfare Society has shown that since 2015 foxes have tested positive for Toxo in other areas, although some still do seem to be ‘hotspots’.
We are learning almost by the day with regards to foxes with this condition as initially we thought it would be impossible to pair up two foxes for companionship, if one or both was suffering from the effects. Our reasons for this was in the fact we didn't think a fox suffering Toxoplasmosis would be able to communicate with other foxes, so could therefore be attacked. We also noted a fox after successful treatment would always be very sleepy and you could often move the sleeping fox to another sleeping area without the fox even waking.
Although a Toxoplasmosis fox could never be released back into the wild (To date) we wondered as to whether we could give a good home to them. They were ideal for this as they were so friendly and seemed to love companionship, and would sit for hours being groomed, never attempting to bite. In an attempt to make their lives better we thought we should really try to see how a toxo fox would get on with another resident fox.
Our first attempts with this was with a fox called Pellow, he went in with a healthy adult but deaf dog fox. The results were that they seemed to get on fine, as they almost seemed to ignore each other. Our second Toxo fox Lewie went in with a vixen that couldn't be released back to the wild as she was too friendly. Again the pairing seemed to work, although at first, the vixen was a little frightened of her new companion. Lewie was also able to jump up on boxes and became quite agile. Sadly Lewie died of Kidney failure maybe as a result of the Toxoplasmosis reactivating, so we feel it is important that any toxo foxes should be retested at least once a year if not twice.
Our third pairing was quite by chance as Aphrodite (Pictured and her story can be read in her album) was exercised each day in one of our enclosures and once she had a walk around she would be taken back to the hospital unit and Dotty, another Toxo positive fox, would then be given a run in the enclosure. Quite by chance I tried both together so they could both have more exercise time whilst I was at hand to step in if needed. The results were amazing. For the two hours that followed, the two vixens played chase, with tails up and displaying usual fox behaviour.
First Aphrodite chased Dotty, then the tables would turn and Dotty would chase Aphrodite. After two hours they were exhausted and both curled up next to each other and slept. In the weeks and months that have followed, they have been observed grooming each other and have got really close. They eat together and there is never any aggression and both will cache food. Dotty who had a lower count than Aphrodite walks up a blank to the next level in the enclosure and will sometimes sleep in the higher box. Both have hunting instincts and will chase an object or investigate an object if it is moving.
Over the course of the months both Aphrodite and Dotty will hide from me at the start but will come out but no longer like me grooming them, preferring it seems, their own company and this is brilliant to see. Aphrodite sadly died a year later when she started having seizures and we believe this was the result of reactivation, again showing a need for regular re-tests.
Our fourth pairing was with Rupert from North London, who had the highest count of all the one's we tested. He was placed in with Ruby from Coventry and instantly they bonded and have become inseparable, laying together in their bedding area and following each other around. Due to circumstances, Ruby & Rupert went to live in an enclosure in Scotland and sadly Ruby died.
What this proves to us is a fox with Toxoplasmosis that will often be put to sleep by other organisations, can be given a new lease of life in captivity and will often go from a sleeping almost dazed fox to a near normal fox when placed in an enclosure with a companion. Cause for concern is still that a great many have died within a two year period, but from our recent research, we may now have an answer to stop this, that could also prove to be a successful treatment for foxes that may have dormant toxo and even active toxo. Whilst we do look for good homes for the foxes that sadly can’t go back to the wild because of Toxoplasmosis, we ensure they go into outside enclosures and with at least one other fox and we always state to the people who kindly take the foxes on that they need to fit into the foxes world, rather than expect the foxes to fit into theirs.
The research we have done already could hold many answers and one fox in particular ‘Adonis’ may have given us some very interesting results into foxes with dormant Toxoplasmosis and then how it effects them when it comes out of dormancy. Our research is ongoing and we have spent thousands of pounds already and will continue to do so until we can get some concrete answers that we hope will benefit foxes brought into our care suffering from this condition and help those already in our care.