MANGE IN THE RED FOX

Content Updated: 29th March 2011

Summary: There are several different types of mange, but that most commonly found in foxes is sarcoptic. Sarcoptic mange is a skin disease caused by a small (2 to 4 mm, or less than one-quater of an inch) parasitic mite (Sarcoptes scabiei), several thousand of which may burrow into a single square-centimetre of skin. Female mites burrow into the skin where they may live for as long as a month. As the mite burrows, tissue fluids and debris are deposited on the surface of the fox’s skin forming a crust that causes intense irritation, and leads to considerable scratching by the infected animal; scratching causes hair-loss and lacerations, which can then become infected by bacteria. Conjunctivitis is also apparent in severe cases, giving the fox a 'crusty-faced' appearance (right), as are changes in behaviour (the infected fox becomes less and less active). Weight loss and organ damage are often evident and, if left untreated, death follows in four to six months. Mange can have profound influences on the fox population; an outbreak in 1994 succeeded in wiping out 95% of Bristol's fox population in only two years.

The most common treatment is the broad-spectrum anti-parasitic medication ivermectin (sold under the name Stromectol in the USA and Mectizan in Canada), although selamectin (an active ingredient in the medication Stronghold) is used by some vets and animal charities. Homeopathic remedies are sometimes employed, the most common probably being Arsenicum album and sulphur 30c; the National Fox Welfare Society (NFWS), for example, sends out hundreds of free 30c treatments every year. There is, however, debate among veterinarians as to the effectiveness of homeopathic remedies because, while they may treat the skin infection, they typically do not kill the mites. There are, nonetheless, many letters from members of the public on the NFWS’s website testifying to the improvements seen with the 30c treatment.

The Details: Mange is a persistent contagious skin infection caused by a parasitic mite. There are two types of mange generally found among members of the dog family, classified according to the mite that causes the infection. Demodetic mange (sometimes called demodicosis or ‘red mange’) is caused by mites of the Demodex genus -- typically D. canis in domestic dogs -- that live in hair follicles and are usually only problematic for animals with a weakened immune system. Sarcoptic mange, by contrast, is more severe. Sarcoptic mange is caused by the mite Sarcoptes scabiei (from the Greek sarkos for ‘flesh’ and koptein meaning ‘to cut’, and the Latin scabare meaning ‘to scratch’) and is the form veterinarians or doctors are referring to when they diagnose mange or scabies, respectively. It is worth quickly noting that there is a third type, Notoedric mange, which is caused by the mite Notoedres cati, hence its other name, feline mange – it is very rare in dogs.

Sarcoptes are mites and, as such, they have eight legs and are classified along with the spiders and scorpions in the Arachnida class; more specifically they are grouped together with the ticks in the taxonomic order Acarina. The 2001 book Parasitic Diseases of Wild Mammals, lists 105 species known to be susceptible to infection by S. scabiei including most domestic livestock, chimps, foxes, badgers, hedgehogs, squirrels, deer, lions, cheetahs, wolves, pine martens, stoats, red pandas, polar bears, seals, porcupines, hares, koalas and wombats. Indeed, the discovery that Sarcoptes mites generally show a preference for certain host species led some authors to divide them into distinct species; the mites causing the fox mange, for example, would therefore be Sarcoptes vulpes. Not everyone, however, is convinced.

In a 1968 paper, Belgian parasitologist Alex Fain presented a detailed morphological and life history study of this mite and argued that, although there was considerable variation among some of his subjects, it wasn’t sufficient to separate them from the type species (i.e. they’re all just Sarcoptes scabiei - pictured, left). Some 30 years later, Fain’s conclusions were confirmed by a team of parasitologists based in Germany, who found no genetic evidence to support taxonomic separation of S. scabiei into distinct species; they concluded it was a single, variable species. There are, nonetheless, several studies showing that mites transferred from their primary host (e.g. a dog or fox) to an alternate one (e.g. a human) rarely survive more than a few days, which certainly suggests some degree of host adaptation. Indeed, in a fascinating paper to the Journal of Parasitology during 1996, a team of researchers at Wright State University in Ohio reported that mites infecting pigs, dogs and humans each produced their own set of unique proteins which they injected into their host.

There is still much to be discovered about the specificity of this mite but, ultimately, the current view is that Sarcoptes scabiei is actually one species with many ‘variants’, which are classified according to their preferred hosts. Mange mites infecting foxes, for example, are generally referred to as Sarcoptes scabiei var. vulpes, while those that parasitize domestic dogs are S. scabiei var. canis, those infecting pigs are var. suis, those causing scabies in humans are var. hominis, and so on. These variants are generally widely accepted, although some authors consider var. vulpes and var. canis to be the same (lumping them together as var. canis and dropping var. vulpes altogether) because dogs and foxes can catch mange from each other and, as Set Bornstein put it in a 1991 paper, “It is not possible by morphological features to distinguish between S. scabies var. vulpes and var. canis” – in other words, the mites look identical.

Mangy foxes and mite modus operandi
Fox mange is most commonly sarcoptic, although demodetic and notoedric mange have been documented. Notoedric mange is apparently very rare among foxes, although in his 1980 opus Red Fox, Huw Gwyn Lloyd suggested that it may be more common than the literature implies, referring to several foxes in Cheam, Surrey that were apparently severely infected with this mite during 1969.

Foxes can contract mange from various sources, including direct contact with an infected individual or carcass, and areas of the territory through which an infected animal has passed (the mites can survive in the environment for several days waiting for a host). Indeed, in 1958, Russian ornithologist Yuri Gerasimov demonstrated that mites could be transmitted to uninfected foxes inhabiting earths (dens) that had previously been used by infected individuals; the Russian outbreak was controlled by fumigating earths with gas to kill the mites. Gerasimov also found that larval mites could survive on the ovipositors (egg-laying appendages) of flies for around 24 hours after the insect had landed on a carcass infected with mange; this raises the possibility that flies may be able to transmit the mite to healthy animals (a mechanism known as phoresy). More recently, it has been found that fluid exuded from wounds caused by the parasites can contain many millions of mites and this probably represents a significant potential source of contagion if left on a fence or at a daytime lying up site.

However the fox comes to be infected, laboratory studies have demonstrated that the mites quickly spread. Male mites mate with females once before dying and, once the female arrives on a new host it takes about ten minutes for her to start burrowing into the outermost layer of the skin (the stratum corneum); she generally creates a burrow in this layer, although she may penetrate much deeper (into the stratum germinativum). The mite uses cutting mouth-parts called chelicerae and specialised hooks on her legs to cut into the skin and is usually fully submerged in just over 30 minutes. As she burrows, the newly-fertilized mite feeds on tissue fluid called lymph and lays eggs; the eggs hatch, first into larvae and then into nymphs that extend their mother’s burrow system and thus the infection spreads over the fox’s body as the mite population increases. In their 2001 book Urban Foxes, Bristol University biologists Stephen Harris and Phil Baker note that a severely infected fox may be host to several million mites, while scientists at the University of Georgia in America have found densities approaching 5,000 mites per square centimetre (or over 32,000 per sq-inch) of skin.

Once the initial contact has been made between the mite and its host there will be a period during which the fox is asymptomatic (i.e. shows no signs of having mange). The time taken for symptoms to develop is referred to as the incubation period and varies according to the individual -- previously infected animals appear hypersensitive to re-infection, meaning symptoms develop sooner than they did first time around -- and the number of mites transferred during the contact. In a series of experiments on captive foxes, biologists in North America found that a moderate application of mites (about 500) led to an incubation period of 20 to 30 days, while a high application (around 2,000 mites) had an incubation of only 9 to 10 days. A similar set of experiments, conducted by parasitologists in Sweden during the early 1990s, found that a low application load (about 200 mites) to three captive foxes produced the first symptoms 31 days later, around the same time that antibodies to S. scabiei var vulpes appeared in the animals’ blood, increasing until more severe symptoms developed 49 to 77 days after the initial infection. Experiments by Susan Little and her colleagues on captive animals estimated that about 5,500 mites were transferred between foxes during infection and re-infection, although captive contact rates may not mirror those in the wild, but are probably more relevant to urban populations than rural ones. (Photo Scabies infection of human patient. The mite can be seen at the end of the burrow to the top right of the image. Photo by Michael Geary and released into public domain via Wikimedia Commons)

Symptoms of mange vary according to the severity of the infection. Low-level infection may present as little more than localised itching and mild hair loss. At some point, however, more severe symptoms usually develop. As the mite burrows and feeds, lymph and debris (e.g. eggs, egg cases, live and dead mites, mite faeces and digestive secretions) ooze out on to the skin’s surface and harden into a ‘crust’ that can be relatively thick. In a short paper to Veterinary Record, parasitologist Peter Bates reported on a young dog fox found dead from mange in a hedgerow on a farm in Surrey (UK) during November 1990 that had 1.5cm (just over half-inch) thick scabs covering its back. The burrowing and excretions cause intense irritation and foxes typically present with intense pruritis (itching). During the 2001 mange outbreak in Wales, farmers reported intensely pruritic foxes stopping to scratch vigorously several times when crossing a small field. Intense scratching, licking and gnawing at infected areas causes wounds that scab over (a process called hyperkeratosis) and this, combined with the skin excretions causes the fur to be lost – this is a condition known as alopecia, from the Greek word alopex meaning ‘fox’ and the suffix –ia used to signify disease (so alopecia is literally ‘fox disease’).

Alopecia (hairloss) on the back and flank of a fox with a sarcoptic mange infection. In the lower image you can see the pronounced hyperkeratosis (skin thickening) and where the skin has started to crack. The cracking of the skin, combined with scratching and grooming lead to lesions that are prone to bacterial infection.

Alopecia is localised at first, usually beginning around the haunches and base of the tail -- presumably this is related to the area being heavily scented and a site of social communication (meeting foxes often sniff violet glands, which are located near the base of the tail) -- spreading quickly forwards. Symptoms are often quick to manifest on the head, most likely transferred while the fox is grooming the affected area. As the infection spreads, the hair loss increases along with areas of raw skin (damaged during scratching and grooming) and the fox, unable to maintain its body temperature without fur and less able to hunt because of the constant itching, begins losing condition. In the advanced stages, a fox will often enter outbuildings such as sheds and greenhouses in an effort to keep warm. As the animal’s condition deteriorates, it becomes susceptible to secondary bacterial infections, caused by opportunistic microorganisms (e.g. Streptococcus and Staphylococcus bacteria) living on the skin. Indeed, in their book Urban Foxes, Harris and Baker described a ‘musty odour’ associated with severely infected individuals and, in his 1980 book Red Fox, Lloyd noted how affected animals develop a “characteristic sweet, ‘mangy’ odour, which may be due to a secondary bacterial infection”. Conjunctivitis is also common in the late stages of the disease, giving a swollen-eyed crusty appearance to the face. In the end, the bacterial infection, starvation (the weakened animal can no longer hunt efficiently) and hypothermia, if untreated, prove fatal.

The general mammalian immune response to a parasitic infection is to destroy the invader by coating it with antibodies that make it susceptible to attack by phagocytes (white blood cells); special white blood cells called eosinophils home-in on the antibody-coated intruder and release the contents of their granules (peroxides and proteins) thereby bombarding the parasite with toxins. We know that some mammals (about 40% of humans and over 80% of domestic dogs, for example) launch an immune response to Sarcoptes mites, which means that if they’re re-infected they fight it on their own; the situation in foxes is unclear. (Photo: Mange often starts on the haunches and progresses rapidly forward, quickly jumping to the head as the animal grooms the affected area.)

In a 1998 paper to the Journal of Wildlife Diseases, a team of biologists at the University of Georgia described the responses of foxes to infection and re-infection with sarcoptic mange. The researchers found that their foxes developed mange within two weeks, after which they were subsequently treated and the condition cleared up. When exposed again, the foxes contracted mange again, with no signs of it being any less severe than the first time; in some cases the foxes remained ‘hypersensitive’ to the mites for four months after they’d recovered from the first infection. This study suggests that foxes do not launch effective immune responses against the parasite as most canids do. In a 1976 paper on foxes in mid-western North America, however, Gerald Storm and his co-workers suggested that these animals may be able to recover from mange on their own, while in 1995 Set Bornstein and colleagues observed a fox suffering from prolonged low-level mange that never progressed to severe mange, suggesting the fox’s immune system was keeping the mites ‘in check’. More recently, Rebecca Davidson at Sweden’s National Veterinary Institute, along with Set Bornstein and Kjell Handeland, presented evidence suggesting that foxes and Sarcoptes mites were adapting to live together. In a paper to Veterinary Parasitology during 2008, the veterinarians described changes in Norway’s fox population between two outbreaks of mange (one in the mid-1990s and another in the early-to-mid 2000s) and found that there were significantly fewer cases during the second study period, with mange prevalence falling from 30% during the 1990s to 6.6% in the early 2000s. The authors concluded:

“These findings indicate that the red fox population is adapting to live with the parasite and that low-grade or sub-clinical infections, and even recoveries, occur amongst exposed foxes.”

Scientific papers aside, the general observations of veterinarians and animal charities seems to be that foxes rarely recover from severe mange on their own, and most die within four-to-six months without treatment. Indeed, in his 1994 book The Complete Fox, St. Tiggywinkles co-founder Les Stocker pointed out that, prior to their work, mange was considered an incurable disease and infected foxes were killed. Fortunately, these days mange is a relatively easily treated disease and even severely infected animals can usually be nursed back to health.

Road to recovery
There are two major medications commonly employed to treat mange: the broad-spectrum (i.e. ‘kill all’) anti-parasitic ivermectin (Stromectol in the USA or Mectizan in Canada), and selamectin, which is found in tick and flea treatments such as Stronghold – both medications are acaricidal, which means they kill the mites. It is often cited that treatment ideally needs to be administered in situ (i.e. given to the fox in some food), rather than the fox having to be captured and treated at a clinic. Capturing the fox is invariably stressful for the animal (and probably the rescuer!) and foxes are territorial, which means that it could be released back into the area several weeks later to find its territory has been taken over by another fox. This seems logical, although foxes live in family groups in many, especially urban, areas and it would be interesting to know whether such animals were less susceptible to this ‘territorial usurping’ when only one animal was removed for treatment. Nonetheless, hospitalization should be a last resort. Unfortunately, while relatively low-level mange can be treated with medication in food, many severe cases make hospitalization unavoidable as the animal (which may be almost bald) needs to be kept warm and requires a transfusion of fluids and complementary drugs to treat dehydration, mange and bacterial infections.

Where treatment in situ is possible, this generally involves putting a few drops of medication in food and giving it to the fox; often several treatments are required. Ivermectin can be taken orally and yields good results, but is toxic to some breeds of dogs (e.g. collies, old English sheepdogs, Jack Russels, etc.) with a particular genetic mutation that allows the drug to pass across the blood-brain barrier into the brain. Consequently, it is important that only the foxes eat the medicated food and this can make vets reluctant to prescribe it. Alternatively, although not licensed as an oral treatment, Vale Wildlife Rescue (after consultation with the manufacturers) found that Stronghold can be administered in food with excellent results. That said, most medications are under veterinary prescription, which means that the vet usually needs to see the foxes and thereby they can be considered under their treatment. You should always seek veterinary advice before attempting to administer any medication. When administered correctly, both medications have success rates approaching 100% and symptoms clear up within two to four weeks. Moreover, these acaricides remain active in the fox’s body (offering protection from the mites) for between two and four weeks after the treatment is given.

The alternative to drug medications is to use a homeopathic or herbal remedy. The basic premise of homeopathy is that using very dilute (and thus essentially safe) solutions of some active molecules can trigger the body’s immune system to fight off an infection. To the best of my knowledge, there is no evidence to even suggest that ‘water has memory’ (and so can ‘remember’ what was diluted in it) or that, in clinical trials at least, homeopathy is any more effective than placebo treatments. That said, the homeopathic treatment Arsenicum album and sulphur 30c -- a few drops of which are added to the food every day for three weeks -- is commonly given to foxes suffering from mange. The National Fox Welfare Society, for example, send out hundreds of free treatments -- they normally cost about £10 ($16 or €12) -- every year and use it to treat foxes taken into their sanctuary in Northamptonshire. On their website the NFWS have many letters from people who have used this treatment with apparently excellent results. The Fox Project in Kent note similarly spectacular results when treating with 30c, although they point out that it is less successful at treating foxes with more than 30% alopecia. I have seen photos from readers showing foxes before and after (with the fox fully recovered) homeopathic treatments; in some cases, all that was offered was additional food and vitamin supplements.

How does the homeopathic treatment work? Scientists generally like to know how things work, although all must accept that there is still much that we have yet to understand. It is fairly easy to grasp how pharmaceutical medications, such as ivermectin or Stronghold cure the fox. Selamectin, the active component in Stronghold for example, becomes systemic (i.e. it’s absorbed into the blood) and circulates around the body, including the skin; the mites ingest the selamectin as they feed and it interferes with their nervous system, causing death (ivermectin works in a similar way). There is, incidentally, some indication that topical treatments (e.g. Frontline - pictured right) may also be effective, although these don’t become systemic; they dissipate through the grease-layer of the skin. It is less easy to understand the actions of homeopathic remedies and, ultimately, nobody really knows what they do. It’s easy enough to ascribe a ‘placebo effect’ among human patients in a clinical trial, but surely the same cannot be applied to foxes, who don’t know that you’re treating them?

On their website, the NFWS suggest that the 30c treatment improves the fox’s overall condition, healing the skin and helping restore vitamin and mineral imbalances, thereby hampering the mite’s lifecycle and making the fox more able to cope with the infection on its own. It is certainly true that mangy foxes are generally underweight. In a study published in the Canadian Journal of Zoology during 2002, a team of Bristol University biologists led by Tabetha Newman report on the nutritional condition and survival of foxes with mange. The researchers looked at the carcasses of 51 foxes collected from the UK between 1997 and 2000 and found that class I (low-level mange) animals weighed, on average, 15% less than uninfected animals, while class II (severe mange) animals weighed 33% less. The biologists also found that some class II animals showed signs of muscle wastage; when fat reserves are exhausted, the body starts metabolising protein for energy (a bit like pulling up the floorboards in a house to fuel the fire). The authors concluded that foxes infected with mange show symptoms of malnourishment, increasing as the disease takes hold – it is interesting to note that this should be so even in urban Bristol, where food is plentiful. It is suggested that fear, pain and/or stress may lead to anorexia in foxes, as is well known in other animals (even as humans most of us know how illness or stress can put us off our food).

It seems conceivable that homeopathic treatment could treat the skin condition, reducing the itching and thereby the scratching; this in turn might permit the healing of lesions and the re-growth of the fur. If the remedy also contains vitamins and minerals this may correct any biochemical imbalances in the fox, improving its general health and therefore its potential for fighting disease and infection. The fox may then just live with a low-level mite infection that flares up only if the animal becomes malnourished or sick from some other source. Alternatively, the remedy may contain chemicals that make it into the blood and are distasteful to the mite (biting flies, called ‘midges’, for example, are reputed to dislike thiamine such that eating Marmite is said to stop you getting bitten), making the fox a less appealing host. It has been suggested that foxes fail to launch an immune response against the mites if they’re immunocompromised -- if their immune system is weakened by some other underlying infection, malnutrition, stress etc. -- and thus the simple act of feeding the fox may help it recover enough to fight the mange on its own. We’ve seen in Bristol that a lack of available food may not be the issue here, although there may be a quality vs. quantity effect (if householders put out higher quality, or more palatable food with the treatment). Finally, there may be an element of coincidence. Fox territories generally encompass several backgardens and mangy foxes tend to be rather conspicuous; it’s possible that while somebody at one end of the street is feeding a homeopathic treatment, one of their neighbours may be treating with a pharmaceutical medication. This is, I must stress, purely speculation on my part, and I urge readers to keep an open mind. I would be very interested to hear from readers who may have better explanations.

Sufficed to say there is still much debate among veterinarians over how effective homeopathic treatments are. I am unaware of any clinical studies comparing the effectiveness of the pharmaceutical treatments to the homeopathic ones and the jury is still very much out. In the end, the important outcome is that the fox is cured, regardless of how it happened.

So, we know that mange can be treated and that severe infections are often fatal without medication, but what happens if treatment isn’t given? What does that mean for other animals that inhabit or visit the fox’s territory and for the fox population as a whole?

Share and share alike
We have already seen that Sarcoptes mites show a preference for (perhaps even adaptation to) certain host species, which makes cross-contamination less likely. Some species are, however, more susceptible than others. In North America during 1972, Gerald Stone and his colleagues conducted a series of experiments to see what other species they could successfully transfer Red fox mites to; mites were freely interchangeable between foxes, dogs and coyote/dog hybrids, but skunks, rabbits, grey foxes, raccoons, opossums, rodents and cats all failed to sustain the infection. Indeed, while possible, transfer of var. vulpes to cats is rare and, on their Fox Website, the Bristol University biologists point out that between 1973 and 2006 there were only 11 such cases worldwide – cats are susceptible to mange, but they usually contract the Notoedres cati mite.

Foxes can transfer their mites to humans, although var. vulpes is not a strain that normally infects people and the mites tend not to survive long. Indeed, in a brief article to EcoHealth, Peter Rabinowitz and Zimra Gordon reported on the case of a wildlife carer who went to her dermatologist complaining of an itchy, lumpy rash that had developed on her neck and chest just over a week after she handled a mangy fox; she was treated with a Lindane cream that cleared the rash up in two weeks. The vet to whom she took the fox also developed a similar itchy, lumpy rash on her stomach and chest, which she did not treat; it resolved itself within a couple of weeks. It seems that although the var. vulpes strain can burrow into humans, it cannot reproduce and thus the population dies out. Over the previous two months, the vet recalled having treated several dogs, living near the golf course where the fox was caught, for mange.

Domestic dogs appear particularly susceptible to contracting mange from foxes (they can also give foxes mange). A series of experiments by Dr Bornstein during the late 1980s found that captive beagles caught mange and developed clinical symptoms (i.e. itching, redness, crusty skin etc.) within a couple of weeks of being exposed to a piece of skin taken from a wild fox. When the fox skin was pressed on to their back, the incubation period was 6 to 9 days and, if the skin was just attached to the side of their cage it took between 11 and 13 days for symptoms to manifest. The dogs started losing hair within three weeks. Bornstein’s studies were obviously conducted in heavily confined quarters, but we have already seen that transfer occurs in the wild and there are many other similar accounts in the literature. The outbreak in Sweden during the mid-1970s, for example, resulted in local dogs contracting mange almost as soon as the epidemic appeared in the fox population. Similarly, in a letter to the Veterinary Record during 2003, for example, W. A. Scott described how, shortly after a fox family with serious mange in Falmouth died, local dog owners started reporting cases of mange in their pets. As with foxes, treatment of pet dogs involves a course of acaricide, such as ivermectin or Stronghold. (Photo: Three Sarcoptes mites in a skin scraping taken from a wild fox with sarcoptic mange. Photo from EcoHealth article, reproduced with permission.)

Dr Storm and his colleagues found they couldn’t move the var. vulpes strain of mite to most of the wildlife they looked at, but there has been some indication that foxes can infect badgers, with whom they sometimes share setts. In a recent letter to the Veterinary Record, a team of RSPCA and Veterinary Laboratory Association vets described a case of severe sarcoptic mange in an adolescent female badger from south-west England, suggesting that cross-contamination from foxes sharing the sett was a possible source of infection. Interestingly, however, in his earlier letter to the same journal, Mr Scott noted that a local badger sett, in which the foxes were sometimes seen, showed no signs of mange.

Sarcoptic mange frequently begins at the base of the tail and around the rump; it is possible that mites are transferred when foxes sniff each other's supracaudal glands (located on the top side of the tail, near the root), which is a common greeting. Foxes may also pick-up the mites by sitting in an area where an infected fox had recently lain. The infection usually begins with mild hair loss and hyperkeratosis on the rump (top) and quickly progresses across the haunches and down the tail (bottom).

Far-reaching Consequences
Sarcoptic mange outbreaks in Australia during the 1940s and 50s reduced the fox population by an estimated 80% and the disease is endemic in many populations throughout Europe, Russia and North America, where there are reports from Ohio and Pennsylvania dating back to the 1950s. The UK has a long history of mange (see Brian Vezey-Fitzgerald’s Town Fox, Country Fox for a review), with an outbreak recorded in the New Forest in Hampshire during 1789, during which the Lord Warden of the Forest worried about the ‘great scarcity of foxes’. In his 1980 book, Lloyd recounts how 18th Century hunters were among the first to recognise the disease as fox hunting became popular and Peter Beckford wrote about it in 1810. Lloyd goes on to note how New Forest naturalist Gerald Lascelles wrote about an epidemic of mange that began in 1895 and raged over much of England for three years before fox numbers began to recover, being plentiful again by 1905. Mange has been epidemic in much of south and south-east Britain since the 1940s but, more recently, Britain experienced a significant mange outbreak that decimated many fox populations. I don’t plan to cover this in much detail here, but the subject will receive attention in the main Red fox article that’s currently under revision.

Mange is often perceived as being a feature of urban living, but this is not actually the case. There is little evidence that urban areas are poor quality habitats for foxes, or that urban animals are more prone to disease than rural individuals. Indeed, the first recorded outbreak among Bristol’s urban foxes was contracted from a nearby rural population. The first fox to be infected was a juvenile male that returned to his family group in the spring of 1994 having dispersed out of the city the previous winter; during this time he was spotted on the rural fringes to the west of the city, where mange was known to be present in the local foxes. The biologists at Bristol University captured the animal in May 1994, at which point he was so severely infected with the disease that he had to be euthanized. Following this, mange was reported in foxes throughout the city, spreading at a rate of almost a kilometre each month, with infections appearing in domestic dogs a month-or-so after it was reported in the fox groups. The epidemic spread throughout the city and, in only two years, the fox population had been reduced by an estimated 95%. With this massive reduction in density came some interesting behavioural changes; the foxes expanded their territories, travelled more widely, changed rest sites more often, and used allotments and woodlands more often than the back gardens they frequented before the outbreak (partly because fewer people were leaving food out for the foxes as they rarely saw any).

Fortunately, Bristol’s fox population has been studied continuously since 1977 and a massive amount of data has been collected; the mange outbreak allowed a unique opportunity to look at how quickly fox populations recovered. The answer, it seems, is very slowly. By 1999, the population was still less than 10% of the pre-mange density and even by 2004 (a decade after the first case) it was only 15% of that of 1994. It seems that even today, the population is still not at 1994 levels, although it has probably stabilised at a new lower level. The reason why foxes take so long to recover from these epizootics (wildlife epidemics) appears to be related to the impact the mite has on breeding performance and population structure. The population is rapidly reduced with heavy mortality of both young and adult foxes (cubs may be particularly susceptible as they don’t have a full-strength immune system, receive a lot of attention from other group members, and share the earth with their siblings) and kept low by reproductive inactivity. In his 1969 book They All Ran Wild, Eric Rolls noted that foxes in the grip of a mange epizootic often failed to breed. Similarly, in a 2007 paper to Mammal Review, the Bristol University team described how severe levels of infection were associated with a lack of breeding females and an increase in male foxes that failed to produce sperm. The biologists concluded that in the advanced stages “mange is sufficiently debilitating to limit individual reproduction” and fewer breeding females, along with more young foxes dying make it difficult for the population to recover. Low fox numbers can, in turn, have significant influences on other species. (Photo: Foxes undergo a protracted moult that lasts for much of the summer, starting at the haunches and moving forwards. This moult can give the fox something of a 'mangy' appearance, such as the very thin tail in this animal, but it is not actually mange.)

Young foxes receive considerable attention from other group members and such social interactions probably aid the spread of mange mite through a family group.

We know from experiments where foxes are controlled on game estates and around breeding bird colonies that fewer foxes generally translate to more prey species. In a study of foxes in the Grimso Wildlife Research Area in south-central Sweden, a group of biologists at the Swedish University of Agricultural Sciences found that while fox populations were kept low by mange during the late 1970s and early 1980s, populations of grouse and hare increased and there was a 30% increase in the number of Roe deer kids. As the fox population began to recover in the late-1980s, the numbers of hares and grouse declined once again. In their paper to the journal Ecology in 1994, the researchers concluded that foxes were key in structuring small game communities in their area by keeping prey populations low. Thus, large-scale mange outbreaks have the potential to lead to increases in prey populations as well as the densities of predators and other animals with which foxes compete for food (pine martins, badgers, hedgehogs, etc.).

So, in conclusion, we can see that mange is a virulent disease that can have potentially devastating effects on fox populations, which are typically slow to recover. This, in turn, can have a profound impact on their prey and those animals with which they share their home range and compete for food with. Mange can, however, be treated and the earlier the treatment is offered the better. If you have a fox visiting your garden that appears to be suffering from mange (and it is worth remembering that foxes undergo a protracted moult during the summer, which can lead to something of a ‘mangy’ appearance), please contact your local wildlife rescue centre to arrange an assessment and discuss appropriate treatment. Most carers, and many vets, will assess and treat the wildlife for free, but they will always appreciate a donation if you can afford it. The mites can be transferred to domestic dogs, but this is easily treated with a course of acaricide as prescribed by a vet. (Photo: A fox showing signs of re-growth of fur following treatment for a severe sarcoptic mange infection. This vixen is nursing cubs, which imposes an additional energetic burden and probably makes her more susceptible to parasitic infection.)

Note: I would like to extend my sincere thanks to Caroline Gould and Tim Partridge from Vale Wildlife Rescue for taking the time out of their busy schedules to answer my incessant questions about mange treatment and provide me with so many photos.

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