Fox colouration is a vast topic, but below are examples of spotted foxes, as reported by My Fox Family (Hungary, 2018) and S. Brown (West Midlands, 2017). I would have to agree with the assessment made by others regarding these foxes; such spots could potentially be the result of novel colour genetics, rather than being health related. Without further veterinary or genetic testing, follicle damage due to parasite bites, vitiligo and leukotrichia are the only known causes of such spots in wild foxes, to date.
Leukotrichia and vitiligo are conditions that produce a white spotted effect within the coat of animals of many species. Animals of any age can be effected and it may progress in time, with the animal turning completely white or developing increasing patches of discolouration as it ages.
"Leukotrichia" is the technical term for what is generally considered to be an acquired de-pigmentation that occurs over an animals lifetime. It is usually progressive in nature, being triggered by illness, stress or environmental factors.
"Vitiligo" is a considered a heritable condition of the immune system that is then triggered by environmental factors. The conditions cause antibodies to be formed against pigment-producing melanocytes. It is the destruction of these melanocytes that leads to the observed de-pigmentation.
White Spotting is a known fox coat colour mutation of the farmed North American red fox. It is linked with the genes that cause leucistic mutations such as piebaldism and whitemark/ringneck morphs. The most common example can be seen in the exploited mutant form known as the 'Georgian fox'. The mutation for white spotting was originally observed in the Whitemark and Platinum foxes of the European fur trade, as described in the book The Red Fox by H.G Lloyd (1980), detailed below;
"Danish Fox Pelts - The Fox pelt on the right is not unlike those of Britain. The one on the left shows the lighter fur on the neck and behind the shoulders; the spiral in the tail is caused by twisting whilst drying. The three centre foxes are unusual in the degree of blackness and spotting in the fur (not due to ticks). The cross of dark fibers over the shoulder is more apparent in these than in the more common forms (Photographed with kind permission of Helge Walhovd, Aarus)."
The Georgian fox, also called the snow mutant, was first documented in Russia in 1943. It is a white fox with black spots on the face, back and feet, but it's markings are distinct in their organization from marble foxes. These foxes are often described as 'freckled'.
The typical Georgian white exists on a silver fox background, with most of the body being white, and patches of black along the back, on the muzzle, face, ears, and legs of the fox. It is distinctive from marble foxes in that their ears usually often solid black.
The gene is incompletely dominant, and is lethal in homozygous condition. Therefore, Georgian foxes should not be bred to one another, nor any other white series coloration besides marbles. These foxes were heavily restricted when they were first discovered during the period of the USSR, and for a time only existed in Russia. They now are present across Europe, but they are not present in the North American pet or fur trade; except for Russian domesticated foxes imported to the US. Georgian white can hypothetically exist with any other coloration (amber, burgundy, pearl, etc.), but only two variations are currently well documented (Georgian white and Georgian red) with another; the Georgian Brown fox, having been bred on a rare occasion.
"The farm breeding of foxes began in Easter Canada in the late 19th Century... with the Georgian White (GW) morph first being described... in Georgia in 1943... Recently, we have shown that a mutation in the KIT gene causes platinum coat color in foxes. Allelic interaction among the GW and platinum coat colors has previously been established through cross breeding of GW and platinum foxes. The mapping of the GW allele.. is thus consistent with the results of the experimental breedings and suggests that GW is also caused by a mutation on the KIT gene"
Only veterinary assessment and genotyping of wild foxes possessing spots, could tell us for sure, how the fox got it's spots 🦊