Rare Horse Diseases

• Anthrax - ""The sudden death of a horse gets the owner's attention immediately, and so do colic and severe diarrhea leading to death. If blood comes from the nose, mouth, or other orifices of the dead animal, the owner should prevent other animals from accessing the carcass, avoid all contact with the carcass, and call a veterinarian or state health official. The cause of death might be the spore-forming bacteria Bacillus anthracis that causes illness and death in livestock in several U.S. areas. However, unusual weather conditions, floods, and alkaline soils can potentially stir up spores deep in the soil and cause anthrax cases in other geographic areas. Anthrax is usually rapidly fatal in horses, so it's unlikely there would be time to treat horses with clinical signs, but you could potentially treat suspected cases very early on or prophylactically treat exposed horses. Special diagnostic sampling techniques and disposal methods are necessary for suspected anthrax cases; in some jurisdictions it might be a reportable disease..."

  People can become ill from dead animals by dermal exposure (through the skin, called cutaneous anthrax) to infected animals, tissues, and soils; inhalation anthrax is possible if spores are aerosolized, which can happen while processing livestock hides or wool..."

• Aspergillosis - "In horses, epistaxis and dysphagia are common complications of gutturomycosis (see also Guttural Pouch Mycosis). The infected guttural pouch is characterized by a necrotizing inflammation and is thickened, hemorrhagic, and covered by a friable pseudomembrane. Mycotic rhinitis characterized by dyspnea and nasal discharge has also been described. Aspergillosis can be a rapidly fatal disease associated with diffuse pulmonary invasion. In these cases, acute enteritis is often a predisposing factor. The colitis is thought to result in a profound neutropenia that decreases the immunocompetence of the host, followed by the invasion of Aspergillus from disrupted intestinal mucosa. Locomotor and visual disturbances, including blindness, may occur when the infection spreads to the brain and optic nerve."
• Coccidioidomycosis - "Coccidioidomycosis is a fungal disease caused by Coccidioides immitis, and less frequently, by Coccidioides posadasii.1It was first recognized as a human disease in Argentina in 1892, and was first reported as a disease of animals in 1918, with a case of bovine infection. Since then, it has been found in both wild and domestic animals, including deer, tigers, mice, rats, squirrels, gorillas, monkeys, dogs, cats, sheep, cattle, horses, and reptiles..." Follow the link at the beginning of this paragraph to read an excellent article that also has images.
• Colitis X, equine colitis X or peracute toxemic colitis is a catchall term for various fatal forms of acute or peracute colitis found in horses, but particularly a fulminant colitis where clinical signs include sudden onset of severe diarrhea, abdominal pain, shock, and dehydration. Death is common, with 90% to 100% mortality, usually in less than 24 hours. The causative factor may be Clostridium difficile, but it also may be caused by other intestinal pathogens. Horses under stress appear to be more susceptible to developing colitis X, and like the condition pseudomembranous colitis in humans, there also is an association with prior antibiotic use. Immediate and aggressive treatment can sometimes save the horse, but even in such cases, 75% mortality is considered a best-case scenario.
  Clinical Signs

  Colitis-X is a term used for colitis cases in which no definitive diagnosis can be made and the horse dies. Clinical signs include sudden, watery diarrhea that is usually accompanied by symptoms of hypovolemic shock and usually leads to death in 3 to 48 hours, usually in less than 24 hours. Other clinical signs include tachycardia, tachypnea, and a weak pulse. Marked depression is present. An explosive diarrhea develops, resulting in extreme dehydration. Hypovolemic and endotoxic shock are manifest by increased capillary refill time, congested or cyanotic (purplish) mucous membranes, and cold extremities. While there may initially be a fever, temperature usually returns to normal.

  Clinical signs are similar to those of other diarrheal diseases, including toxemia caused by Clostridium, Potomac horse fever, experimental endotoxic shock, and anaphylaxis.

  Causes

  To date, the precise causative factor has not been verified, and the disease has been attributed by various sources to viruses, parasites, bacteria, use of antibiotics and sulfonamides and heavy metal poisoning. Other possible causes include peracute salmonellosis, clostridial enterocolitis, and endotoxemia. Of interest is that Clostridium difficile toxins isolated in the horse have a genotype that is also that of the current human "epidemic strain," which is associated with human C. difficile-associated disease of greater than historical severity. C.difficile can cause pseudomembranous colitis in humans, and in hospitalized patients who develop it, fulminant C. difficile colitis is a significant and increasing cause of death.

  Horses under stress appear to be more susceptible to developing colitis X. Disease onset is often closely associated with surgery or transport. Excess protein and lack of cellulose content in the diet (a diet heavy on grain and lacking adequate hay or similar roughage) is thought to be the trigger for the multiplication of clostridial organisms. A similar condition may be seen after administration of tetracycline or lincomycin to horses. These factors may be one reason the condition often develops in race horses, having been responsible for the deaths of the Thoroughbred filly Landaluce, the Quarter Horse stallion Lightning Bar, and is one theory for the sudden death of Kentucky Derby winner Swale.

  The link to stress suggests that the condition may be brought on by changes in the microflora of the cecum and colon that lower the number of anaerobic bacteria, increase the number of gram-negative enteric bacteria, and decrease anaerobic fermentation of soluble carbohydrates, resulting in damage to the cecal and colonic mucosa and allowing increased absorption of endotoxins from the lumen of the gut.

  The causative agent may be Clostridium perfringens, Type A, but the bacteria are recoverable only in the preliminary stages of the disease.

  The suspect toxin could also be a form of Clostridium difficile. In a 2009 study at the University of Arizona, Clostridium difficile toxins A and B were detected, large numbers of C. difficile were isolated, and genetic characterization revealed them to be North American pulsed-field gel electrophoresis type 1, polymerase chain reaction ribotype 027, and toxinotype III. Genes for the binary toxin were present, and toxin negative-regulator tcdC contained an 18-bp deletion. The individual animal studied in this case was diagnosed as having peracute typhlocolitis, with lesions and history typical of those attributed to colitis X.

  Use of antibiotics may also be associated with some forms of colitis-X. In humans, C. difficile is the most serious cause of antibiotic-associated diarrhea, often a result of eradication of the normal gut flora by antibiotics. In one equine study, colitis was induced after pretreatment with clindamycin and lincomycin, followed by intestinal content from horses which had died from naturally-occurring idiopathic colitis. (A classic adverse effect of clindamycin in humans is Clostridium difficile-associated diarrhea.) In the experiment, the treated horses died. After necropsy, Clostridium cadaveris was present, and is proposed as another possible causative agent in some cases of fatal colitis.

  Diagnosis

  At necropsy, edema and hemorrhage in the wall of the large colon and cecum are pronounced, and the intestinal contents are fluid and often blood-stained. Macroscopic and microscopic findings include signs of disseminated intravascular coagulation, necrosis of colonic mucosa and presence of large numbers of bacteria in the devitalized parts of the intestine. Typically, the PCV is >65% even shortly after the onset of clinical signs. The leukogram ranges from normal to neutropenia with a degenerative left shift. Metabolic acidosis and electrolyte disorders are also present. There is leucopenia, initially characterized by neutropenia, which might evolve in neutrophilia. Moreover, haemoconcentration is noted with an increase in the packed cell volume; total proteins are initially increased, but changes into a lower than normal value. The most significant laboratory finding in colitis X is the increase of total cortisol concentration in blood plasma. Histopathologically, the mucosa of the large colon is hemorrhagic, necrotic and covered with fibrohemorrhagic exudate, while the submucosa, the muscular tunic and the local lymphonodes are edematous.

  Treatment

  Treatment for colitis-X usually does not save the horse. The prognosis is average to poor and mortality is 90% to 100%. However, there are ways to treat the condition, and one famous horse that survived Colitix-X was U.S. Triple Crown winner Seattle Slew, who survived colitis-X in 1978 and went on to race as a 4-year-old. Large amounts of IV fluids are needed to counter the severe dehydration, and electrolyte replacement is often necessary. Flunixin meglumine (Banamine) may help block the effects of toxemia. Mortality rate has been theorized to fall to 75% if treatment is prompt and aggressive, including administration of not only fluids and electrolytes, but also blood plasma, anti-inflammatory and analgesic drugs and antibiotics. Preventing dehydration is extremely important. Nutrition is also important. Either parenteral or normal feeding can be used to support the stressed metabolism of the sick horse. Finally, the use of probiotics is considered beneficial in the restoration of the normal intestinal flora. The probiotics most often used for this purpose contain Lactobacillus and Bifidobacterium.

• Cryptococcus - "Cryptosporidium parvum is a protozoal intestinal parasite that can cause significant diarrhea in humans and young calves. Foals have been shown to shed C. parvum in feces, but generally they don't appear sick, and people in contact with affected foals have developed cryptosporidiosis (the disease associated with this parasite). Therefore, good hygiene, such as thorough hand washing, should be practiced when handling foals..."
• Gutturomycosis - "...In horses, epistaxis and dysphagia are common complications of gutturomycosis (see also Guttural Pouch Mycosis). The infected guttural pouch is characterized by a necrotizing inflammation and is thickened, hemorrhagic, and covered by a friable pseudomembrane. Mycotic rhinitis characterized by dyspnea and nasal discharge has also been described. Aspergillosis can be a rapidly fatal disease associated with diffuse pulmonary invasion. In these cases, acute enteritis is often a predisposing factor. The colitis is thought to result in a profound neutropenia that decreases the immunocompetence of the host, followed by the invasion of Aspergillus from disrupted intestinal mucosa. Locomotor and visual disturbances, including blindness, may occur when the infection spreads to the brain and optic nerve..." Gutturomycosis
• Histoplasmosis Blastomycosis similar to histoplasmosis - "Histoplasma capsulatuin is a dimorphic fungus. It exists in nature as a septate mycelium, usually found in the soil. At the tips of the hyphae of the mycelial phase, there are small microconidia that are infective, usually as aerosols, but also as ingested fomites. Exposure in endemic areas usually results in a mild self-limiting pneumonia in immunocompetent animals, including humans..." Follow the link at the beginning of this paragraph to read the entire article.
• Salmonella in Horses - "Salmonellosis affects humans, horses, most mammals, and birds. It can cause debilitating--and even deadly--diarrhea. Salmonella bacteria can affect both foals and adults, and they spread easily by horse-to-horse contact and by fomites (shared tools, water buckets, hands, etc., on which bacteria can "hitch a ride" to the next victim). Seemingly well horses can harbor the bacteria, and when stressed, they can shed it or become ill. "The environment can be contaminated by birds, rodents, or other wild animals shedding the organism in feces, including contaminating feed for horses," says Simon Peek, DVM, MRCVS, PhD, Dipl. ACVIM, clinical assistant professor of large animal internal medicine, theriogenology, and infectious disease in the department of large animal internal medicine at the University of Wisconsin. Salmonella has received attention lately due to several outbreaks of nosocomial disease (infections picked up at a hospital by an animal that did not have that infection upon entrance) in various teaching hospitals.

  Peek says there are more than 2,000 types of Salmonella, including several that affect horses. Most common is S. typhimurium, a type that also infects cattle and people. All types are zoonotic (affect animals and humans) except for one type that only infects humans..." This is a quote from an excellent article by theHorse. Follow the link above to read more.

• Vesicular Stomatitis - A zoonic disease.