Melissa holds a Bachelor's Degree in Biology and is a plant and animal enthusiast with multiple pets.
If you’ve had a pet rabbit suddenly die from unknown causes, you’re certainly not alone. Unfortunately, despite their sweeping popularity as smaller pets, rabbits can contract a significant number of conditions and illnesses that can lead to their sudden death without even showing symptoms or they can have deceptively mild symptoms before rapid death.
Rabbits, like most prey animals, will disguise their underlying illness for as long as possible to the point that when they finally show symptoms, they are near death. The illnesses and accidents that can potentially cause this are numerous. In fact, listing every possible cause is beyond the scope of this article. The best way to find out why your rabbit suddenly passed is to have a necropsy performed.
Signs and Symptoms of Illness in Rabbits
Because rabbits are adept at disguising their illness, it is imperative to take notice of any changes your rabbit undergoes. Rabbits are tricky animals, and to compound this issue, immediately finding a vet with rabbit experience is a problem for most owners. You might want to start your search for a vet before any of these issues worsen. Some of these symptoms warrant immediate care. Most of these symptoms are non-specific and may have multiple causes.
- Anorexia: If your rabbit refuses to eat, it is referred to as anorexia. This can be the cause of your pet’s problem or be a secondary symptom of an underlying disease. Anorexia can result from diseases and stress.
- Unusual Feces: Feces that are abnormally sized, liquidy, mucous-covered, strong-smelling, too soft or hard, and anything else differing from the usual can indicate disease.
- Diarrhea: This is associated with many lethal diseases in rabbits. Your rabbit has diarrhea when it passes no firm fecal pellets and only excretes soft or liquid stool with little control. This will most likely be due to enteric disease associated with a pathogen .
- Perineal soiling: A common finding in pet rabbits that points to illness 
- Hiding: Rabbits will tend to mask pain and appear otherwise normal when they are experiencing disease, but they may start to obscure themselves from view more often.
- Unusual Posture: “Flopping down” or pressing the stomach to the ground can indicate abdominal pain.
- Tooth Grinding: Loud tooth grinding can be a sign of abdominal discomfort.
- Distended Belly: Can indicate gastrointestinal diseases.
- Chewing: Frantic chewing of paper, wood, or bedding may occur when a rabbit has stomach pain.
- Dyspnoea: Difficulty breathing and open-mouth breathing is a sign of severe respiratory distress .
- Inappetence: When a rabbit refuses to eat, many problems arise.
- Weight Loss: An extremely common occurrence in sick rabbits.
- Exercise Intolerance: Can be associated with many diseases including cardiovascular issues.
- Lameness: Can be trauma-based, viral or neurological.
- Gut Stasis: May be called a disease in itself but is actually a common condition associated with a number of diseases that can be life-threatening.
Infectious Causes of Sudden Death in Rabbits
The domestic rabbit, also known as the European rabbit (Oryctolagus cuniculus), are prone to a multitude of infections that may cause them to die suddenly. Pathogens that may cause mortality in rabbits include those which are bacterial, viral, and protozoan.
Bacterial Causes of Sudden Death
- Tyzzer's Disease: Caused by Bacillus piliformis, rabbits may be infected by the ingestion of spores and exhibit sudden and profuse watery diarrhea, lethargy, dehydration, and rapid death within 1-2 days after symptoms in the majority of cases .
- Rhinitis or Coryza: A common rabbit disease that causes inflammation of the nose and many bacteria types may be involved. .
- Colibacillosis: Enteric disease caused by E.coli with diarrhea, febrile, and anorexia as a symptom. It is common in Europe and seen less frequently in the United States .
- Staphylococcus: A common disease that causes fatal septicemia, S. aureus is a normal rabbit flora that can opportunistically proliferate when the rabbit is stressed. This bacteria is involved in the development of mastitis, which causes the mammary glands to become painful, swollen, turn blue or red, and sometimes abscess. It is also involved in many other conditions .
- Bordetellosis: The bacterium Bordetella bronchisepticum can cause rhinitis in conjunction with P. multocida, or pneumonia by itself .
- Salmonellosis: An uncommon, but serious disease caused by Salmonella spp. It has a high mortality rate, resulting in diarrhea and rapid death by septicemia .
The bacterium Pasteurella multocida is an extremely common cause of diseases in communally housed rabbits that is most often harbored within rabbits' nasal passages and pharynx without any clinical signs. It can sometimes cause rhinitis (snuffles) or asymptomatic low-grade infections when combined with stressful conditions . It is resistant to antibiotic therapy and can be harbored without clinical signs, transmitting to other rabbits housed within the same room by the oral-respiratory route.
The multiple, potentially lethal pathologies include abscesses, pneumonia, genital infections, "wry neck", mastitis, pyometra, and eventual septicemia, however, pasteurellosis can be associated with the infection of any organ or system. Pneumonic pasteurellosis is another condition caused by the bacterium .
Second to pasteurellosis in commonality within domestic rabbit populations are enteric diseases. Young, newly-purchased rabbits are susceptible to enteric disease, which may be caused by a number of pathogens. This is due to pathogenic exposure, crowding, lower stomach pH, the stress of weaning, and non-established gut flora. Adults rarely acquire enteric diseases .
Before the disease takes hold, rabbits may undergo a change in their gut flora that allows the proliferation of C. spiroforme, including weaning, (especially feeding high energy, low fiber diets to weanlings), stress, antibiotic therapy, concurrent illness, parturition and lactation. Rabbits with this disease often succumb rapidly after exhibiting diarrhea .
The bacteria Clostridium spp. or Escherichia coli normally reside in the rabbit gut but can proliferate and produce powerful enterotoxins under certain conditions in younger rabbits (especially recently weaned), including crowding in small spaces. Poor nutrition, such as a low fiber diet, has also been cited as a potential cause. Generally, the result of this disease is diarrhea, collapse, and then sudden death due to toxemia, dehydration, and electrolyte loss. Death usually occurs in 12-24 hours .
- Yersiniosis: Pseudotuberculosis, caused by the bacterium Yersinia pseudotuberculosis, sometimes occurs in rabbits with generalized, non-specific symptoms such as weight loss. It may be contracted from food sources contaminated by mice and rats . It is rare in domestic rabbits .
- Chlamydia: A disease caused by Chlamydia spp. that has a high mortality rate .
- Listeriosis: Uncommon disease caused by Listeria monocytogenes, results in sudden death due to septicemia in acute cases .
- Pseudomonas spp., Moraxella catarrhalis, and Mycoplasma spp. are pathogens found in some upper respiratory diseases .
- Tuberculosis: A rare disease in domestic rabbits that causes inflammation within the lungs, liver, kidneys, digestive tract, and others .
- Myocardial disease may be caused by pathogenic agents such as Pasteurella multocida, Salmonella spp., and Clostridium piliforme, although this is rare .
- "Young Doe Syndrome": This describes the occurrence of a rabbit that has recently given birth and dies suddenly when the litter is about 4 to 10 days of age. Sometimes diarrhea is observed although often there are no symptoms. The cause is enterotoxemia or staphylococcal mastitis .
Signs of Disease can be Subtle
Viral Causes of Sudden Death
Viruses are non-living pathogens that can cause mild to severe disease in pet rabbits.
Rabbit Hemorrhagic Disease virus is an acute, highly infectious, and fatal disease that originated in Europe and is only lethal to European rabbits. Symptoms of this deadly disease include lethargy, anorexia, depression, tremors, ataxia, and epistaxis.
The incubation period of the disease is 1-3 days and rapid death occurs 5 to 72 hours after symptoms appear from organ failure, resulting from acute necrotising hepatitis, pulmonary edema and hemorrhage. Sometimes rabbits can show no symptoms and die suddenly, and others may develop a chronic form and die in 1-2 weeks .
- Cancer-causing viruses: The Shope papillomavirus is spread by biting insects and causes keratinous carcinomas on or around the head.
- Myxomatosis: In the European rabbit, infection with the myxoma virus, which is a pox virus, causes severe disease with high mortality. One unique symptom is edema (swelling) of the eyelids and "droopy" appear eyes as well as nodules on the ears. It is transmitted mainly by fleas and mosquitoes and can cause death usually within 1-2 weeks, but sometimes in as little as 4 days due to secondary infection depending on the strain involved. There is no treatment .
- Rotavirus: Widespread in domesticated rabbits causing severe, watery diarrhea and dehydration .
- Rabbit fibroma virus: Closely related antigenically to myxoma virus and spread by biting arthropods, this virus can be lethal to newborn rabbits .
- Herpes Virus: Some herpes viruses in rabbits cause acute mortality .
- Coronavirus: There are strains of coronavirus that affect young rabbits (3-10 weeks old) and cause enteric disease, pleural effusion disease and cardiomyopathy. Death within 24 hours may occur after diarrheal symptoms begin . In rare cases, it can be involved with myocardial disease .
- Rabies: Rabbits housed outdoors may rarely contract rabies and succumb to the disease in 3-4 days after neurological symptoms develop .
Protozoan Causes of Sudden Death
- Coccidiosis: This is the most common cause of enteric disease in rabbits, which can also occur concurrently with other pathogens. Hepatic coccidiosis is also common . The pathogens are in the genus Eimeria and parasitize parts of the intestine . Controlling the presence of coccidia oocytes is important with younger rabbits and may be accomplished with impeccable hygiene. Unfortunately, removing the presence of coccidiosis entirely is nearly impossible . Rabbits in the terminal stages of the disease may have diarrhea or constipation .
- Toxoplasmosis: While it is common for pet rabbits to be exposed to toxoplasmosis due to the presence of free-ranging cats around rabbit food and water sources, infections resulting in symptoms are rare. Severe cases can result in anorexia, fever, paralysis, lethargy, and other problems in addition to acute death in 2 to 8 days .
- Cryptosporidium: Some weanling rabbits may have enteritis or emaciation, generally with co-contamination from other pathogens .
- Giardia: Giardiasis has been found to cause death in some young rabbit populations due to catarrhal enteritis .
- Encephalitozoon cuniculi is a significant pathogen to pet rabbits that causes renal and central nervous system disease and is even opportunistic in immunocompromised humans .
Gastrointestinal Disease and Sudden Death
- Diverticulitis: This is an uncommon disease that involves infection in the colonic mucosa and submucosa due to weaknesses in the muscle layers. Perforation of the mucosa and abscess formation may result.
- Gastric Ulceration: It is common for rabbits that suddenly pass away to have a gastric ulcer.
- Gastric Dilation: Caused by intestinal obstruction, paralytic ileus, or mucoid enteropathy.
- Hepatic lipidosis: A disease with non-specific clinical signs and obesity as a predisposing factor in most cases.
- Ileus: A common finding in rabbits that has several different causes, including dental disease, malnutrition, stress, and pain .
- Paralytic ileus: An uncommon condition involving complete loss of gastrointestinal motility.
- Caecal impaction: Stress, dehydration, or ingestion of products that can't be degraded by the caecal microflora cause impaction .
- Small Intestinal Obstruction: This is unfortunately a common condition rabbits get that can cause collapse, shock, and rapid death. This emergency may be caused by the formation of a solid, impacted pellet, possibly formed by the rabbit’s ingestion of hair, followed by re-ingestion of the droppings containing the hair. This can also be caused by foreign bodies (seeds, carpet fiber, etc.) and tumors within the GI tract. Hairballs may develop due to insufficient roughage or boredom . Tapeworms may also cause intestinal obstruction .
- Epizootic Rabbit Enteropathy/Mucoid Enteropathy/Mucoid Enteritis: A condition mostly affecting young, farmed rabbits (6 to 8 weeks) and is rare in pets, it may result from hypomotility in the caecum and colon . This disease may be caused by more than one pathogen. One unique symptom is polydipsia, as well as dehydration, "jelly-like" stool, anorexia, caecal paralysis, weight loss, and distended abdomen .
Diseases Associated with Old Age
Cardiac disease in rabbits is based mostly on anecdotal evidence and is more common in larger breeds. Symptoms of cardiac diseases in rabbits are generally breathing difficulty, exercise intolerance, lethargy, anorexia, and sometimes swollen extremities. Rabbits are adept at hiding illness until they reach congestive heart failure .
- Heart Failure: Symptoms are hind limb and generalized weakness, weight loss, organ dysfunction, dyspnoea, and anorexia.
- Dilated cardiomyopathy (DCM): One of the more common heart diseases in rabbits, there will be no symptoms until myocardial function is significantly compromised.
- Endocardiosis: The most common finding is a systolic parasternal murmur.
Neoplasia and Cancer
As pet rabbits are living longer, they can develop cancers . The most common cancers are those of the urogenital, hemolymphatic, and integumentary systems.
The most common neoplasm found in domestic rabbits is the adenocarcinoma, both uterine and mammary . The second is lymphosarcoma. Domestic rabbits can also succumb to neoplasms associated with oncogenic viruses, namely myxomatosis in the European rabbit. Generally, a sign of cancer includes low body condition .
Other neoplams that can metastasize into a terminal condition include:
- Leiomyoma and Leiomyosarcoma
- Cutaneous fibroma
- Squamous Cell Carcinoma
- Intestinal lymphoma
- Hepatic cholangiocarcinoma
- Bile Duct Adenocarcinoma
- Mammary Adenocarcinoma
- Squamous Cell Carcinoma
- Basal Cell Adenoma (rare)
- Bone tumors (rare)
- Thymoma (cases occur 1 to 4 years of age)
- Plant Toxicosis: Outdoor rabbits may access poisonous plants such as milkweed, foxglove, and lupine. Pesticides are also sometimes problematic .
- Heavy Metal Poisoning Toxicity: Common household metals include lead, mercury, silver, zinc, copper, arsenic and iron. Free-roaming rabbits are at risk for ingesting toxic amounts. Inappetence, anorexia, and slow gut motility may occur .
- Lead Poisoning: Lead poisoning is a common finding in pet rabbits due to lead-based paint. Weight loss, anorexia, lethargy, ileus, and neurological symptoms may occur .
- Heat Stress / Acute Shock: Rabbits are susceptible to heat stress and heat stroke because they cannot sweat. They may be affected by temperatures as low as 82C (89F). Rabbits suffering from heat stress may exhibit open-mouth breathing, seizures, depression, ataxia, and coma before death .
- Trauma: It is common for pet rabbits to fracture their spine from incorrect handling .
Dying of Fright?
There are many anecdotal claims that rabbits can "die of fight" or perhaps due to an associated heart attack initiated by a traumatic event. As this article has shown, rabbits can contract a large variety of underlying diseases and show little or no symptoms. Therefore, while there is a possibility of extreme stress causing sudden death in rabbits, it's more likely that the event exacerbated a concurrent disease.
- Pregnancy Toxemia: Also called ketosis, this disease causes sudden death in pregnant rabbits or those that have recently given birth. They exhibit lethargy, breathing problems, and sometimes neurological issues .
- Mastitis ("Blue Breast"): Usually found in lactating or pseudopregnant females, there are many clinical signs, including pain, anorexia, rejection of young, and depression. Can lead to mammary carcinoma in cystic cases .
- Inadequate maternal care can result in high mortality to neonates. This is generally the first litter .
Other Causes of Sudden Death in Rabbits
- Obstruction: Rabbits are known to be curious eaters and their esophagus can become obstructed with food. They may not show any signs of this other than inappetence .
- Ulcerative Pododermatitis (sore hocks): This disease is necrosis of the skin on the metatarsus, caused by pressure from wire-bottomed flooring. Some rabbits with this disease may show no symptoms other than lesions on the foot. Rabbits with this disease may have subclinical septicemia and be reluctant to eat, as well as reduced body condition . The main bacterium involved is Staphylococcus aureus .
- Myiasis/Fly Strike: This is a secondary disease caused by certain flies being attracted to a rabbit's soiled perineum. This area may have accumulated caecotrophs because the rabbit is not consuming the material due to another problem, including obesity, dental disease, and arthritis. Fly eggs are laid between the skin folds, which hatch and cause tissue damage.
- Liver lobe torsion: A spontaneous disease that may be caused by endotoxic shock or paralytic ileus in 24 to 48 hours.
- Arterial Bone Metaplasia: Characterized by wasting and anorexia [espinosa].
- Pyloric Stenosis: This disease can be acquired or congenital in young rabbits, and acute forms cause sudden death. Signs include anorexia, hunched posture, weight loss and listlessness .
- Acute and Chronic Renal Failure: A common problem in older rabbits.
- Trichobezoars (hairballs): Low fiber diets may result in the clumping of hair in the rabbit's digestive track which causes impaction. Affected rabbits may stop eating for up to 3 weeks before death if this isn't treated .
- Dental Diseases: While tooth problems don't usually cause sudden death, the resulting severe inappetence can lead to your rabbit not eating and other issues. In some cases, dental disease can lead to acute decompensation. Common conditions include incisor malocclusion, sharp points on the teeth, periodontal disease, maxillofacial abscess, and periapical changes .
The above is meant to be a guide for rabbit owners to explore potential causes of death for their beloved pets, but given that many diseases show the same symptoms (or none at all), and that there can be more than one illness or associated condition that affects the final outcome, diagnosing a pet rabbit definitively is not possible without a necropsy.
If your pet dies suddenly, it is important to refrigerate his or her body immediately, with the hopes of sending it to be examined, ideally within a three day time period.
References and More Information
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This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.
© 2020 Melissa A Smith