From newest to oldest.

Update October 2019

By Dr.Hanneke Roest
Translated by Karen Pedro

New Corona virus in the Netherlands
Since 2016 a fair number of young ferrets have been experiencing serious health issues in The Netherlands. At first, a connection was made between an increased use of raw and prey diet among ferrets. Almost all breeders changed the past decade into (partially) raw and prey feeding, and advised their kit buyers to continue with it. At the end of 2018, extensive research showed that this raw meat diet was not the cause of the disease, but definitely made it worse. With the aid of “Werkgroep rauwvoeding fret” (now Werkgroep-fret corona mutatie) Dr Roest was able to examine a number of young ill ferrets and succeeded in identifying the symptoms and clinical presentation.

Mid-2019 a new type of Corona virus has been found by Dr B. Haagmans (Erasmus MC) in feces and organs of these young ferrets. No other viruses, bacteria or parasites were found. This led to the suspicion that this new type of Corona virus is the cause of the illness. Already known were 2 earlier types of Ferret Corona virus:

  1. Since 1993 the enteric Corona virus, which can cause diarrhea, but often remains a-symptomatic
  2. Since 2004 the systemic Corona virus, which affects several organs. All infected ferrets decease

This new Corona virus is most likely a mutation of earlier Corona viruses. The progression of the disease is chronic and most ferrets die of complications. The transmission of the new virus is likely to be via stool. Right now the virus is suspected to have spread in several places in The Netherlands, as well as abroad. It can be easily transmitted at breeders, shelters and guesthouses.

Still a lot of ferrets remain ill, without their owner noticing. Knowledge of ferret illnesses and related behaviour, specific nauseous symptoms, are frequently missed or misread. To add to the confusion, the ferret shows normal behaviour, in addition to the behaviour of a sick animal. Ferrets which are living in multi-ferret households and in businesses (ferret-groups), will keep on eating due to food competition. Even if the particular animal is in poor condition. While not eating would be the signal for owners to get really worried. Because of this, often ferrets are only presented at the vet in an advanced state of the illness.

Divergent symptoms are shown by the affected ferrets, depending on the severity of the infected organ-system. This means ferrets do show a wide range of symptoms. Often a combination of symptoms. Frequently seen is the combination of GI-tract issues and a chronic middle-ear infection. Following symptoms can be present:

  1. Symptoms of being unwell
  2. Symptoms of GI-tract issues
  3. Symptoms of throat problems
  4. Symptoms of chronic middle-ear infection
  5. Symptoms of reduced fertility
  6. Symptoms due to complications


The virus is a major problem with the diagnosis of this disease. Abnormalities found in urine, blood and feces are non-specific; they do develop for other conditions as well. Another major problem is, that in pathology almost no macroscopic changes are noticeable. Even when submitted tissue samples, only slight deviations were found; which do not match with the severe symptoms of these animals. In other words, even in severely  ill animals, very little is found at necropsy. This complicates the diagnosis extremely. The reason why it took so long to find the underlying condition. Additional methods like immunohistochemistry, RT-PCR, ELISA tests used with the other ferret Corona viruses, or from other animals are unable to detect the virus. At this moment the virus is not detectable in ill ferrets.

The course of the disease:
It is likely that kits are already infected in the litter. From the moment of leaving the litter they fall ill, due to the stress. During their first year of life various organ systems can get affected.

The gravity of the illness depends on the amount of problems caused by secondary infections of bacteria and parasites. A raw and prey diet is strongly discouraged. The disease occurs with “ups and downs”. Some periods are better, other periods worse. These periods are connected to: shedding and seasonal change (warm summertime), and times of stress. Ferrets without territorial stress (solitary housing) are better off and seems to be in less pain. They do lack the food competition, which means they need more encouragement to eat.

A curative treatment, in which the animal is completely healed, is not yet possible.  Nevertheless an owner can do a lot to make life as pleasant as possible for the ferret, which enables these ferrets to have a reasonably normal life.

  • Avoid stress: 
    • Preferably no surgery for castration; rather use Suprelorin© implant for chemical castration. Additional, this has a positive effect on the adrenal glands. If it looks like the implant effect seems to fail after two weeks, one has to keep in mind it might have not been placed into the ferret. A new one can be inserted.
    • Every owner wants to go on vacation now and then. Best is to find a sitter at home or take the ferret with you, if possible.
    • Do not cross-breed with (wild)polecats. The offspring is certainly not healthier and just as vulnerable for the virus. Hybrids do have greater (territorial) stress issues.
    • A ferret is a territorial animal. Best is to keep it solitary, 1 ferret per household. In that way it will have its own territory.
  • Adjust diet:
    • The GI-track is extremely sensitive in these ferrets and endures little; do not feed anything containing possible pathogens, like raw meat or prey animals.
    • Ferrets which experience pain while eating, due to the chronical middle ear infection, thrive on soft food like kibble mush, soaked kibble or brittle kibble which parts easily in the mouth. However a severely nauseous ferrets has difficulty with liquid food. In that case, add some RCC (Royal Canin Convalescence) to make it more attractive.
    • During a weaker period it is important to feed very tasty and highly digestible food.
  • Medication:    
    • Consult medication with treating veterinarian. Very often prolonged treatment with anti-nausea medication is needed. It makes life of these ferrets much more pleasant.
    • Due to weak resistance(immunity), these ferrets are highly sensitive to secondary infections with bacteria and parasites (Giardia, Coccidiae, cryptosporidium). If that is the case, adequate treatment is needed.
    • Pro- and prebiotics are not recommended. In most cases of tested ferrets; it worsened the health condition.
    • Laxative administration during shedding is recommended to prevent fur balls, which can easily develop in the poorly functioning digestive system
  • Proper hygiene:
    • Corona viruses do not stay contagious in the area for long. However, they do so in unsanitary conditions, like dry stool rests.
    • Muck out stool daily. Empty and clean thoroughly the litter boxes once or twice a week. Swop litter boxes every week, to store and dry the previous used one for a week.
    • Clean food and water bowls/bottles daily. Use multiple bowls and bottles, like with the litterboxes.
    • Secondary infections with Giardia and Coccidia ask for additional hygienic measures.
    • After the death of a ferret, and if not having other ferrets (in the house), it is recommended to thoroughly clean cage, attributes and surroundings. Afterwards disinfect with Virkon©S or a steam cleaner. All bedding needs to be washed on 60°C. After that it is advisable to wait at least for 2 months, before bringing in a new ferret.

The future:
We are aware the virus is already widely spread. At the moment the only place where the virus can be detected is at the Erasmus MC in the Netherlands. This centre is dedicated to human viral research. Right now there is no concern whatsoever about the transmission of this virus to humans. There is insufficient funding (yet) for extensive further research. Yet this new systemic corona virus is of great scientific value, and research will continue.
There is no diagnostic test available yet, which makes the purchase of a new ferret difficult. One cannot be certain if the ferret is infected or not. For the many sick ferrets, we cannot provide proof of infection with the new Corona virus either. Only through good clinical and additional research, and eliminating other causes, a presumptive diagnosis can be made.
Another difficulty is, that although the ferrets show severe clinical symptoms, very little to mild changes are visible in necropsy, pathological and tissue tests. Even well experienced veterinary pathologists do miss the disease, because so little is demonstrated.

Ferrets are strong animals. There is a good chance they could handle the disease better in future. It also has shown with several ferrets, that good solitary housing and nourishment, food adjustments and adequate medication, they can have a reasonably normal to good life. Further diagnostics and new medication will be the accent in further research. For breeders searching new breeding stock could be a possibility, but it will be hard to know if new animals are free from the new Corona infection.

The research is not finished yet. Due to the infectious nature of the virus, we have made this information public.
We are still in need of funds and commitment of everyone. But thanks to the support and commitment already given by you, we have been able to discover the possible cause. Not in the least: we know now how to best support the affected ferrets.

Would you like to contribute to the research? Please do so at the bottom of this page.

Update July 2019

The research is in its final phase. In the near future we will be able to tell more about the cause of the "raw food problem". It is already clear that raw food is NOT the cause. There is a contagious infection, where the bacteria in the raw food are making the disease more serious and with a greater chance of complications and fatalities. The name of the disease will therefore be changed in the near future.

Hanneke will continue to look for optimal treatment and ways to prevent this disease in the upcoming months. There is still a lot of work to do. In September she / De Frettenkliniek expects to open (partially) again with caution, as Hanneke is recovering from a burnout due to everything that has happened with the ferrets and this disease in 2018. It has certainly and unfortunately had a lot of impact.

Update May 2019

Written by Dr Hanneke Roest

Currently the Erasmus University is busy with the scientific research to find out the source behind the raw food issues among the Dutch ferrets. To be able to continue, new ferrets will be brought in for further research. The "Werkgroep Rauwvoeding Fret" is an important part in the research and still is in need of as much support as possible.

The research up until now showed strong suspicions of:

  1. There is a primary pathogen causing the disease.
  2. A raw and prey diet seems to worsen the condition of the ferret, but is likely not to be the original source of the disease. Due to the amount of bacteria and parasites naturally found in those products, affected ferrets will present a more severe disease and early deaths. A fact also shown during the study of Leanne at the University of Utrecht. At present it is strongly recommended to avoid raw meat products for ferrets.
  3. It is highly probable that the primary cause of this issue is contagious among ferrets. Passing from mother to kit for example.

A thorough scientific research is long-term and costly. It takes time, but we are getting there and are confident that we figure out what is the primary cause. Many possible causes already have been ruled out. Thanks to many ferret-lovers, who selflessly supported in various ways. Many contributed financially or are planning to do so.

During a weekend in May I will be giving lectures at a congress in Germany, on which many international veterinarians will be present. This issue will definitly be presented. International contact is of great value in this.

Update February 2019

After a lot of research (clinical-, urine-, blood-, bacterial-, parasitical-, and post-mortem tests) we already found out there is a lot more going on then just a disturbed intestinal microbiome.

It seems that the found pathogenic bacteria and parasites in the ill ferrets, could strike as hard due to another primary pathogenic organism entering the body with the raw food. The found bacteria and parasites do make the ferret (seriously) ill, but it looks like there is a “missing link” present as well. Something we are going to search for the coming months.

Evident is that the disease is passed on from generation to generation, and seems to manifest in increased severity each generation. In other words many kits of last year are seriously ill, without having eaten raw meat at any time. It also becomes clear, that ferrets living together (in the same household) for some time, can infect each other.

Ferret-vet Hanneke Roest will need more time for the necessary research. The University of Utrecht uses student Leanne to help her with the research for a full-time period of four months. With data on the patients of the Ferretclinic she can make identification of the problems and evaluate if it is possible to prove the increased health issues in Dutch ferrets due to raw meat and prey animal diet, to a scientific certainty.

In addition, Hanneke Roest shall be visiting fellow vets abroad in this matter. To facilitate this the Ferretclinic will be closed for at least three months, from 1 February 2019.

Update May 2018

Sunday the 20th a small seminar in the form of a Ferretday has taken place. The aim was to raise more funds for the ongoing research and to give an update of developments.
We would like to share these developments with you. It is just an update for now as the research still is in progress.

The past few months ferret-vet Hanneke Roest has been working real hard to try to sort out the recent ferret health problems, concerning mainly the young ferrets.
One common point stands out in all involved ferrets; they all had been raw fed at some point in their life. Either commercial raw, prey animals, game or meat for human consumption.

In 2017 an article has been published in one of the leading veterinary magazines, The Veterinary Record, about a Dutch research done at RIVM (Bilthoven) and the Veterinarian Clinic of the University of Utrecht, concerning possible pathogenic bacteria and parasites in raw meat petfood. This research as well as the publication must meet strict criteria. For this research a variety of available commercial raw petfood branches had been tested. A few shocking fact from this study were: in 23% of the products an E. Coli type bacteria was found,which can cause kidney failure in humans; 80% of the tested products contained antibiotic resistant E. Coli; Salmonella was detected in 20% and Listeria in 50% of the products: the parasites Sarcocysts (23%) and Toxoplasma (6%) showed up as well. All these bacteria and parasites are also dangerous for ferrets.
The available meat in The Netherlands to produce these petfood products is all waist material from the bio-industry. Since 2007 meat producing farmers and breeders are forced by the government to put in less antibiotics, which may result in a higher amount of bacteria in meat. Meaning that regular butcher meat isn’t always suitable to use in a raw meat diet either. Many recalls of (supermarket) meat due to bacteria contamination have occurred in the past years. For us humans it is also advised to thoroughly heat the meat we use.

As the use of commercial minced raw pet meat has been discouraged the past time, many ferret breeders, -owners and –rescues switched (partly) to prey animals. Due to the increased demand for prey animals, like mice, there was a shortage on the market for it. Therefor suppliers weren’t able to provide the high-quality SPF mice or rats anymore and had to turn to commercial prey animal breeders abroad. We do expect the living conditions of these animals to be at least very questionably.

To date, following emerged from the research

Since the start of the Workgroup 11 ferrets have been euthanized for the research. Five of them have had a complete necropsy at the University of Utrecht. The other six have had the necropsy at the Ferret clinic and samples of diverse material and organs were send for testing and cultures to a pathological laboratory in Germany. Another fourteen ferrets, which are still alive, have been used for additional research; material has been send for cultures and other tests.

  • Almost all the examined animals were having chronical inflammations in stomach, bowel (intestines), pancreas, gallbladder, liver and kidneys;
  • There were found eosinophils, remarkably often, in diverse organs as well as in blood. These are a type of white blood cells, involved with the combat of parasites and immune reactions in a body (like allergies);
  • A variety of bacteria has been found, including a pure culture of entero-pathogens like resistant (Haemolytic) E. Coli, resistant Pseudomonas and Campylobacter;
  • Among others, bacteria have been found in still born kits (pup) and in uterus inflammation;
  • In some ferrets an inflammation was found in the brain or mid- and inner ear. An area very difficult to examine;
  • One ferret demonstrated an inflammation in the mid ear and from there an inflammation of the brain and even the spinal cord, caused by a multi resistant E. Coli bacteria. This ferret was also having the same type of inflammation with eosinophils like the other ferrets of the program.

Virus study hasn’t been done, for it is very complicated. Known viruses like Corona, Aleutian Disease (ADV) and other detected viruses in ferrets show other type of disease as seen in these cases.

Five years ago E.Coli bacteria were found in examinations as well. Back then they were treatable with regular antibiotics.

Given the amount of eosinophils detected, it could indicate towards parasites. Additional research has been done for it. No parasites were found, not in stool, nor in tissue or blood. It is highly unlikely parasites are the cause of these extensive chronical inflammations. 

Many breeders had issues with uterus inflammation (pyometra), mammary gland inflammation (mastitis), stillborn kits and non-conceiving jills.

It has had some difficulties to map out the research. A variety of specialists are involved and consulted to aid and interpret some found results, like Nico Schoemaker, Yvonne van Zeeland and Paul Overgaauw (microbiologic and parasitologic specialist) from the University of Utrecht. Thanks to the intensive efforts of Hanneke Roest we can indicate what’s going on.

The one thing in common of all the participating ferrets in this research is the fact they have had raw meat and/or prey animals (mostly at a young age already or even in the litter). Ferrets adore raw and thrive on it, specially kits. This and other reasons is the main factor why raw and prey is extensively used among breeders and pet owners. Breeders and owners were giving it with the best of their intentions. The health problem occurs in all breeders. 

What is probably going on

The intestinal health (microbiome) of very young ferrets is destroyed because of the pathogenic bacteria found in raw meat and prey animals. An alteration of the intestinal health occurs, with less healthy bacteria which sickens the animal.

Given the many eosinophil reactions seen in the GI-tract and the absence of parasites, we can assume that an immune (defense) response is going on due to the altered microbiome and the damage in the intestines made by the pathogenic bacteria. There is a direct link with a healthy microbiome and the immune system (defense) of human and animal.

The asymmetrical immune response and pathogenic bacteria are responsible for a long-term illness. These ferrets have permanent damage in the GI-tract and became hyper sensible for almost everything given by mouth: intolerance for food and medication. They suffer from permanent nausea specially when eating and nutrients aren’t totally absorbed; therefore they are prone to lose weight.

Even if the initial bacteria are gone, the activated immune response will keep the illness last. Breeders who gave raw meat in the past will continue with the illness for quite some time. The altered microbiome is actually passed from mother to kit. A kit is supposed to be sterile (without any contamination). During birth, lactation and from the skin it receives the microbiome of the mother. Normally it would be a healthy cocktail of bacteria, but in this case, it is the altered microbiome either with or without pathogens. In case of being fed with a raw meat diet, the problem will only increase.

An urgent advice to all ferret owners

Do not feed any raw meat, prey animals or raw egg to your ferret. It is an absolute myth that gastric acid kills everything.

The following symptoms can be seen in ferrets with the illness:

  • Losing weight;
  • Changes in stool (from normal to loose or slimy; bad smell; abnormal colour);
  • Poor appetite or abnormal eating behaviour;
  • Abnormal behaviour; lethargic/calmer or hyperactive;
  • Nausea;
  • Bad coat or difficulties with shifting fur.

As a nauseous ferret can be difficult to recognise, a follow up below of symptoms which indicate nausea. Not all ferrets behave equal, so not all symptoms need to be present. Nausea is easier to spot given liquid food, like RCC (Royal Canin Convalescence support).

  • Refusing the RCC or not liking it;
  • Eating the RCC from the edges of the bowl and eating with breaks (seconds) in between/ interim eating;
  • With doubt to start eating;
  • Licking around the mouth/lips; smacking;
  • Digging kibble (or other food) out of the bowl and consume it on the side or somewhere else;
  • Pointing backwards or sideways with the head while eating; tilting the head;
  • Trembling/shaking or bristled tail/fur while eating;
  • Grinding teeth or pawing at the mouth;
  • Chewing fabric, strange objects, side of the litter pan/pet toilet;
  • Hiccups;
  • Lying flat after eating;
  • Walking or standing with a high curved back/ 4 feet close to each other;
  • Needing to be fed on the lap or with aid (of a finger, spoon etc);
  • Shaking its head while eating.

How to proceed?

At this moment there is no treatment available to cure the ferrets from this illness. The found pathogenic bacteria are not easy to treat. A ferret is also an animal with a very sensible GI-tract, which is easily damaged by medication. Current available antibiotics to deal with this type of bacteria is not suitable for ferret treatment, without compromising the stomach or bowel.
Obviously, the research will continue and certainly efforts are being made to find a satisfying treatment.

Sadly to say, but the affected ferrets are gravely or terminally ill for now. It also became clear that affected ferrets can pass the illness (pathogens) on to other ferrets, animals and humans. Strict care and hygiene are essential to prevent spreading to other animals but even more important; to humans.
We are dealing with a very complex condition, which can be spread in different ways and won’t be remedied in the near future. Besides the difficult search for effective medication to treat the chronical inflammations, we are dealing with (heavily)damaged microbiome in ferrets which can’t be cured fast and easily. There hasn’t been done any particular research on a ferret’s intestinal health before. Even more, the study of human microbiome still is in progress.

In summary: we are dealing with a serious and very complex issue. Nevertheless, as said, we will continue the research.

In particular we want to express our thanks to Hanneke Roest. Because of her boundless commitment and enormous involvement, we have reached this far in the research already.

Update January 2018

We would like to share an update concerning the developments in research on behalf of our workgroup.
Again we want to express our gratitute towards all contributors, old and new. Thanks to your support we are able to finance this research!

In the meantime a number of ferrets have had a thorough examination and we have some first results. We want to share as much as possible with you, but right now sequel research is being done and interpretations with other specialists are being made. Therefore conclusions can't be made yet, but we are heading in the right direction trying to find answers.

Some raw fed and ill (young) ferrets have been researched. Inflammations have been found in the gut, gallbladder, liver, pancreas and kidneys. It seems diverse pathogenic bacteria and possibly parasites might be the cause of it. These pathogens are mainly found in raw meat and prey animals. Further research is done with these pathogens, trying to discover an evident proof to be the possible cause of the problems we see with young and (young) adult raw fed ferrets lately. After receiving more results we can try to develop the right treatment, targeted for the specific pathogens. The last part could be difficult, as a great variety of pathogenic bacteria has been found.
Additional research is done with the possibly related mid-ear issues. This process takes much more time, as bones of the skull need to be decalcified.

For now the most important advice towards owners/caretakers of ferrets: Do NOT feed raw meat or prey animals until more knowledge is collected about the pathogens and their possible damage they can cause in health and welfare of ferrets!

Once more we like to appeal to all ferret lovers and owners to help us. Only with your support, we will be able to continue this project. Specially now it seems we are heading in the right direction and additional research is of great value to find answers.

Workgroup-ferret corona mutation (previously Workgroup Rawfed Ferrets)
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