Horse Diseases Paul R Earl Facultad de Ciencias Biológicas Universidad Autónoma de Nuevo León San Nicolás, NL, Mexico.
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Major infectious diseases are discussed, along with heaves which is an allergy. Colic is caused by the endotoxins of intestinal bacteria in some cases, and in many others by abrupt dietary changes, obstructions or gas. Nonetheless, the major cause of colic is damage to the circulation of the intestinal wall by bloodworms.Most of these diseases like pneumonia in foals relate more to raising young horses on farms than to infections in adult work or racing horses. However, encephalitis viruses can kill many adults in somewhat unpredictable outbreaks. West Nile Virus is the 2004 threat, but much vaccinated against.
An effective disease control program with some emphasis on prevention is part of a total management for proper health, nutrition, reproduction, growth and performance. Such a program would contain the control of intestinal parasites, administration of several vaccines and other such concerns given here, but briefly.The eradication of horse diseases lies in the distant future. Meanwhile, better understanding of the role of vaccination is encouraged.
ColicGet that horse up and walking. He got casted, because he was rolling because of abdominal pain. Casted means that he was trapped against the stall wall and could not get up. He could not get his legs under him. Pull him off the wall by the tail or halter. Pain has many possible causes like endotoxins from intestinal bacterial infections. The central symptom of colic is pain. Therefore treat the pain with analgesics or tranquilizers.
The causeof colic might be inadequate blood circulation in the intestinal wall.Bacterial endotoxins may interfere with the synthesis or effects of inflammatory mediators that in turn affect: 1/ Pain, 2/ Fever, 3/ Increased pulse, 4/ Reduced tissue perfusion, 5/ Inhibition of intestinal motility, 6/ Expansion of intravascular fluid volume, 7/ Depression, 8/ Hemoconcentration and 9/ Leukopenia.
EtiologyMany cases of colic involve bacterial endotoxins. “Something” has caused the loss of the integrity of the gut, and the vascularization of the intestinal wall. Expect several possible causes, not one that is easily identified. Once it is established that an infection is active, longacting IV terramycin or another choice of antibiotics can supply appropriate treatment. More, the fundamental and physiological basis of the colic have not been treated. What are emboli?
DiagnosisSigns of painful distress such as sweating are obvious. The horse may evince colic by pawing with the forelegs, but impatient yet normal horses may paw the ground. Rolling on the ground is the strong sign of colic. Fever may be part of colic along with endotoxicosis.Normal resting pulse rate is 36 beats/minute. The respiration rate is 8-16 breaths/minute.
TreatmentExcellent prompt responses follow the injection of a painkiller like flunixin meglumine at 1.1 mg/kg IV, IM or less 1-3 times through 24 hours.Another good painkiller is chloral hydrate administered as a 12 % solution IV slowly (over 5 min) or orally. The dose can be 22 mg/kg IV (10 g for 450-kg horse). Administration through a catheter is ideal because it can cause a severe perivascular reaction. The onset of action is 15-20 min when administered IV. The duration of action is up to 12 h.
PreventionGood grass-based forage, clean water and the control of parasitic roundworms should be enough to prevent most colic. Grains and concentrates seem less important than the hay. However, if a racehorse is not eating up, overexcercise is the likely cause, and new problems even including colic and certainly including lameness can follow by pushing the horse passed its natural limits. The racehorse pushed passed his limits will go off his feed of oats. Still, fatigue or the like is rarely involved in colic.
TetanusThe microbe Clostridium tetani is responsible for causing the muscle rigidity often seen in tetanus, more commonly known as lockjaw. The organism is found in most soils and enters an animal’s body through dirty, neglected wounds and especially via punctures. The exotoxin which C. tetani produces binds to the nerves at the site of the injury and then travels to the spinal cord and brain.
EtiologyTetanus is caused by anaerobic (no oxygen) clostridrial bacteria, everpresent Clostridium tetani which produces spores thatlive in the soil.It is often a fatal disease via the production of toxins. However, tetanus often associated with deep wounds is controlable with antibiotics. Rusty nails, barbed wire and other hazards that produce cuts can lead to seriously threatening tetanus for all mammals.
DiagnosisA stiff gait, rigid extremities, a sawhorse stance, not eating and overreaction to sounds are signs of tetanus. They appear about 2 weeks to a month following infection, but can be seen earlier depending upon the amount of toxin produced. The toxin prevents muscles from relaxing. Once a muscle has contracted as in closing the jaw, it cannot return to its original relaxed state, thus creating always observed rigidity. Death results from either an inability to breath or due to seizures.The toxins demyelinize nerves (myelin is the insulation, the covering of nerves), resulting in dysfunction shown as stiff muscles.
TreatmentA variety of antibiotics like terramycin can successfully treat the infections, but not damage already done by toxin.Antitoxin IM or IV can be given to neutralize toxin. Note that oid means like. Then toxoid is like (modified) toxin.
PreventionTwo products are available for protecting horses against tetanus. These are tetanus antitoxin and tetanus toxoid. Tetanus antitoxin gives immediate but short lived protection. It is given to horses not previously vaccinated that have a wound or to newborn foals from unvaccinated mares. It will impart passive immunity a short while. Tetanus toxoid gives long-acting protection, taking 2 weeks for antibodies to develop. This vaccine is given as 2 shots, one month apart, followed by a yearly booster. Foals can be given the vaccine beginning at 3 months of age. Pregnant mares should be given the vaccine one month before foaling.
StranglesThe symptoms are severe, complications are common and at present there is no effective vaccine for the disease. Antibiotics such as penicillin can control and eliminate strangles best if the disease is detected early.
EtiologyStrangles is caused by Streptococcus equi, group C, which is a highly contagious purulent lymphadenitis and pharyngitis. However, other strectococci are also involved: S. equi, S. zooepidemicus,S. dysgalactiae subspecies equisimilis and S. pneumoniae capsule Type III.Some horses become longterm asymptomatic carriers. Vaccines are available in the form of injectable extracts or as live, attenuated organisms given intranasally. However, their use is somewhat controversial and indicated for horses at risk.
DiagnosisSwelling and infection of the throat region with fever and a cough. The horse may be unwilling to eat. There is often a nasal discharge, which may be serous or mucoid initially and later purulent.Abscesses may form in the retropharyngeal or mandibular lymph nodes, in this area, 10-14 days after initial signs. Persistent drainage from the submandibular or pharyngeal areas can occur. Cranial nerve dysfunction may occur in cases of retropharyngeal abscesses affecting the recurrent laryngeal nerve. Both PCR and ELISA have been tries with S. equi.
TreatmentVancomycin, clindamycin, levofloxin, tetracycline (tetramycin) and of course penicillin will control strangles. Penicillin G or tetramycin can be given most easily in the feed, but this is not done. It is not in the tradition !
PreventionWe have a very common disease and immune carriers. Then foals rather than adults are the problem. Prevention could be through vaccination, BUT the results of research are poor. Can be given nasally. Strangles like many horse diseases can be eradicated of course, but the reality is far in the future.
ParasitesRoundworms are SO COMMON and SO DAMAGING that they should be much better controlled. WHY NOT ? Because MANY owners and trainers think parasites are a normal part of horse life WITHOUT knowing about the ferocious damage.The strongyle group of equine roundworms includes large and small strongyles. They are the most important internal parasites of horses because they are the most common and because of the type of damage the immature stages do to the horse. These worms are called bloodworms.
The 3 large strongyles are 1/ Strongylus vulgaris (bloodworm or redworm), 2/ S. edentatus and 3/ S. equinus. Small strongyles have more than 40 species and are called cyathostomes. Larvas develop from eggs in a week or so. They are surrounded by protective sheaths. The infective third stage larvas migrate up and down blades of grasses, waiting to be eaten by a friendly horse. Ingested larvas migrate through the intestinal wall into the arteries.
The larvas of another large strongyle, 2/ S. edentatus, localize in the cecal or the portal veins and cause perivascular thickening. The liver becomes swollen, looks bluish-red and has the white larvae embedded under its capsule. Prolonged infestation causes chronic fibrosis, tending to lead to peritonitis and adhesions. The third large strongyle, 3/ S. equinus, produces submucosal cysts in the liver, pancreas and intestine. Small strongyles (cyathostomes) cause less harmful reactions.
DiagnosisBloodworms are diagnosed from feces with a qualitative flotation method in a centrifuge. A quantitative procedure is the Stoll or McMaster technique, which uses a counting chamber to sum eggs/g of manure. With the 6-11 month prepatent period (egg to mature adult) for large strongyles, infections will not be evident until weanling or later. Transound scanning andradiographic arteriography are diagnostic tools that complement rectal palpation. Acute horses can have fever, poor appetite, rapid weight loss, depression, lethargy and colic.
TreatmentIvermectin liquid and doximectin gel are most excellent dewormers that knock out bot fly larvas. So does milbemycin. Many anthelmintics are active against large and small strongyles. Benzimidazole (e.g., fenbendazole) among very many dewormers works well. Migrating larvas can be treated effectively with thiabendazole or fenbendazole daily for 5 days, 2 doses of oxfendazole on alternate days or ivermectin. Fecal examinations will help. Start deworming foals at 2 months of age every 2 months for the first year. Deworm adults 4 times a year.
PreventionSanitation, no crowding and good management offer the best control of roundworms. Disinfection of the environment, particularly water tanks and feeders, decreases the horse's exposure to any infective larvae. Fecal samples taken say twice a year or before and after treatment will guage the effectiveness of dewormers. Deparasitizing will vastly reduce the number of nematode eggs in the pasture.