In February 2016 a forest ranger reported finding a dead fox (Vulpes vulpes) in the Dutch province of Gelderland. As it was the fourth report out of this area over a short space of time the carcase was submitted for post-portem exam at the DWHC.
The fox, an adult female in poor nutritional status, was moulting, and had mild alopecia with a superficial wound on the tail, possibly caused by the large numbers of ectoparasites including ticks that were observed. The most significant pathology and the most likely cause of death was parasitic pneumonia caused by Toxoplasma gondii . This protozoan parasite is found all over the world and can affect numerous species of mammals and birds. The life cycle of Toxoplasma involves definitive (felids that have not previously been infected) and intermediate (all warm-blooded animals) hosts. Several weeks after infection in cats that have not previously been infected, millions of eggs are produced and excreted in the feces. It is also believed that cats may episodically excrete eggs if they become immune suppressed. The eggs can survive for up to 1.5 years in the environment. These oocysts are the source of infection of intermediate hosts such as mice and other small rodents and birds which may consume food or water from a contaminated environment. Although these are the most common intermediate hosts, theoretically all warm-blooded animals are susceptible to infection with Toxoplasma. Tissue cysts form in the intermediate hosts and these are a source of infection for cats and other predators such as the fox. Furthermore, it has been shown that infected rodents lose their flight-response, making them easy prey. Indeed a Spanish study showed that 65% of foxes tested positive for Toxoplasma whilst in Belgium, 98% of the tested foxes were infected with this parasite. It is important to note that a positive blood test is only an indication that an animal has been infected with Toxoplasma at some point in its life and not necessarily that infection was associated with clinical signs. As with infection in cats, foxes infected with Toxoplasma are not believed to develop disease except on rare occasions when the vital organs such as the lungs are involved which may lead to death.
Previous study results involving toxoplasmosis:
Toxoplasmosis in red squirrels
Hares don’t only get tularemia…
Toxoplasma in a stone marten
You can report finding more than one dead fox or observing a fox behaving unusually prior to dying on the submission form on our website. We would also like to hear if you find a dead fox with mangy, bald or alopecic areas.