Equine Infectious Diseases Flashcards
- Larvae L3 migrate though portal vein to the liver (peritoneum and retroperitoneum space)
Strongylus edentatus / equinus
- Migration of the larvae and the corresponding immune response can result in thrombosis of the cranial or anterior mesenteric arteries leading to colic and infarction of the bowel
- Severe colic (infarction of a mesenteric artery)
- Verminous arteritis - colic with an associated painful mass at the root of the mesenteric - damage to the cranial mesenteric artery and its branches
- Antihelmintics: Benzimidazoles, pyrantel and ivermectin
- Rectal palpation: painful enlarged root of the mesentery
Strongylus vulgaris
- Colic in foals causing intestinal impaction
- Likely t predispose young foals to develop pneumonia
- Roundworm
- During migration in foals damage the lower respiratory tract and carry bactera
Parascaris equorum
- Foal heat diarrhea
- Migration through the lung causing damage
- Prevention: Treatment of post-partum mares with ivermectin.
- Transmitted to foals in the mare’s milk.
- Ivermectin or Oxibendazole are effective
Strongyloides westeri
- Culicoides hypersensitivity (sweet itch)
- Allergy to the saliva of the gnat. Seasonally, in the warmer months.
- Horses are pruritic and develop lesions on the poll, mane and tail form self trauma.
- Ventral midline can occur.
- More chronically, scarring can occur.
- Recurrent seasonal pruritus during summer months.
- Ventrum or dorsum, depending on the species of the fly.
- Horse develops type I hypersensitivity, developing excoriations, alopecia, and thickened skin as a result of scratching. Flies more active during dusk and dawn.
- Treatment: controlling the fly population.
- Extremely pruritic
Culicoides
- Larvae of the stomach worm migrate and emerge creating granulomatous lesions around the eye, male genitalia, or lower extremities.
- Inside the granuloma - dead larvae
- Granulomatous skin lesions that often contain the small calcified larvae inside.
Habronemiasis
- Dermatitis due to hypersensitivity to dying microfilariae
- Alopecia and scaling of the ventral midline, face and pectoral region.
- Ventral midline dermatitis is also commonly associated
- Diamond shape lesions “bull’s eye”. Annular lesions of alopecia and scaling
- Nonseasonal
- Uveitis, conjunctivitis and keratitis. Uveitis is caused by aberrant migration of the microfiliariae, when they die and inflammatory response is generated.
- Numerous annular lesions of alopecia and scaling in the face and neck.
- Signs result from hypersensitivity of dying microfilariae. Most horses will remain asymptomatic. Lesions: patchy to diffuse alopecia, erythema and scaling.
- Usually not pruritic.
- Most common parasitic cause of uveitis
Onchocerca cervicalis
- Equine lungworm. Horses housed with donkeys highest risk.
- Generally does not cause clinical signs in foals, however, can cause cough and respiratory signs in adults
- Definitive host: Donkey.
- Infective larva ingested and migrates through the mesenteric lymph nodes to the lungs - adults and produces eggs that are coughed up, swallowed and passes in feces
- Diagnosis: Baermann. Other techniques: Transtracheal wash (eosinophils, and possible parasite, ova or larvae).
Dictyocaulus arnfeldi
- Horse bot fly (Gasterophilus spp)
- Prevention: Administer ivermectin twice annually, once early summer and again fall
- Frequently asymptomatic but treatment is recommended because bots can cause gastritis, and annoyance and stress to the horse. The larval instars can cause stomatitis and colic
- Life cycle: complete metamorphosis (3 larval instars) only one generation per year. Cycle starts wth female ovipositing eggs (early summer) on hears front legs, abdomen, flanks and shoulder. Eggs develop into 1st instar (forced to emerge by horse licking) - larvae crawl to mouth and ingested - gingiva 28 days. Larvae molt to 2nd stage move into stomach. 2nd and later 3rd stage attached to the lining of stomach (non-glandular portion) - remain immobile 9-12 months. 3rd mature - detachpass int he feces. Larvae dried in soil - pupate and remain for 1-2 months (late winter and early spring)
- Cause Gastritis
- Yellowish eggs noted on the medial aspect of cannon bone fore limb.
Gasterophilus
- Verminous encephalomyelitis (Halicephalobus deletrix, Draschia megastoma, Hypoderma, Strongyloid nematodes).
- Aberrant migration through CNS is uncommon; causes neurologic disease.
Helicephalobus deletrix
- “Myeitis”. Sarcocystis neurona.
- No changes in CSF
- Any age. Asymmetric neurological signs, multifocal disease of the CNS.
- FDA-approved treatment: Ponazuril. Anticoccidial compound wth cidal activity. Trimethoprim-sulfamethoxazole + Pyrimethamine
- Diagnosis: Clinical signs. Western Blot, IFAT, PCR
Equine protozoal myeloencephalitis (EPM)
- Sarcoptes scabei
- Treatment: Oral ivermectin and topical 2% lime sulfur spray. 2 treatments at 14 day intervals.
- Severe itching, skin thickening and crusting, usually around the head, neck and ears.
- Diagnosis: clinical signs and response to therapy (skin scraping usually unrewarding - very deep)
- Quarantined to avoid spread.
Sarcoptic mange
- Equine protozoal myeloencephaitis (EPM)
- FDA-approved treatment: Ponazuril. Anticoccidial compound wth cidal activity
- Historically combination with trimethoprim sulfa
Sarcocystis neurona
- Horn fly. Feed on blood.
- Ventral midline dermatitis (horses housed near cattle)
- Multifocal, round, crusty lesions ventral abdomen not particularly pruritic
- Fly found around horns, back and sides of cattle on cooler days, affect the ventral abdomen on hot sunny days.
- Economicloses
- Treatment; insecticides sprays, dust bags, insecticide feed additives
Haemtobia irritans
- Mite: Chorioptic mange
- Affects distal limb region and can extend to ventral abdomen
- Pruritus distal limbs,particularly feathered areas
- Irritation, scabbing, and alopecia of the fetlock area, self-induced trauma due to pruritus
- Most common in winter months and causes intense pruritus
Chorioptes equi
- Burkholderia mllei (previously known as Pseudomonas mallei)
- Endemic: Middle East, Asia, Africa, and South America
- Horses, donkeys, mules, and small ruminants
- Horses can become chronic and occult carriers that shed
- Potential zoonotic pathogen
- Forms: nasal gliders, pulmonary glanders, and cutaneous glanders (Farcy)
- Nasal: high fever, loss of appetite, labored breathing with cough. Viscous mucopurulent discharge or crusting around nares. Ulceration upper respiratory passages - form of star-shaped cicatrices “stellate scars”. Regional lymphadenopathy, may rupture or adhere to deeper tissues.
- Pulmonary: over several months, starting as fever, dyspnea and cough. Lung lesions commence as light colored nodules surrounded by hemorrhage or diffuse pneumonia. Nodules can become caseous or calcified, discharge to the upper respiratory tract. Nodules in other organs.
- Cutaneous: over several months, cough and dyspnea. Nodules developed in subcutaneous tissue along course of ymphatics - thickened cord-like lesions coalesce into a string “farcy pipes”. Nodular lesions of other organs.
- Identify bacteria in smears from fresh lesions as many extracellular straight G(-) rods with rounded ends.
- Diagnostic tests: PCR, ELISA and Western Blot. Important: international trade: CF (complement fixation), serology and mallein test. Mallein test most reliable, sensitive and specific; involves injection of mallein purified protein derivate intradermally into the lower eyelid. Read 24-48 hr - positive reaction (edematous swelling or purulent discharge).
- No treatment - humanely destroyed + affected carcasses burned and buried.
Glanders
- Streptococcus equi ssp equi
- Lymph node abscessation (antibiotics are contraindicated - will prolong the course of the disease)
- Spread by direct contact - isolation
- Diagnosis aspiration of lymph nodes
- Treatment - lance abscesses centrally and dispose all material to prevent spread
- Mucopurulent nasal discharge, lethargy, depression. Markedly enlarged mandibular and retropharyngeal lymph nodes.
- Lymph nodes aspiration: purulent inflammation and G(+) cocci with large capsules
Strangles
- Associated with Pulmonary abscesses (radiographic findings: two lines represent fluid or pus capped by gas within cavitary lesions)
- Clinical: weight loss, fever, tachypnea
- Older foals (2-6months)
- Cough, increased respiratory rate, fever, wheezes on auscultation, abdominal tucking,
- Transtracheal wash: Gram(+) pleomorphic rods on cytology
Rhodococcus equi pneumonia
- Fever, lethargy, tachycardia, limbedema, CBC: leukopenia, neutropenia, thrombocytopenia and microscopic observation of a morula within the neutrophil, ventricular arrhythmias, ataxia, petechiations, icterus, fever.
- Diagnosis PCR assay
- Formerly Ehrlichia equi. Infects primarily neutrophils and form inclusion bodies which consist one or more coccobacillary organisms within these cells knows as morula
- Petechiation icterus and ataxia.
- Treatment: Oxytetracycline
Anaplasma phagocytophilum
- Dermatophilus congolensis. G(+), non-acid fast, facultative anaerobic actinomycete, branching bacteria
- Crusting dermatitis in large animals, when there is high moisture on the skin as well as mechanical irritation
- Horses with long, wet hair oats are often affected.
- Lesion on the dorsum, and pasterns described as paintbrush lesions
- Diagnosis with direct smear preparation
- Treatment, keep the hair coat clean and dry and penicillins if severe lesions.
- Sticky matted hair on the dorsum wth multiple crusts that have purulent exudate under them
- Bacteria typically enters skin that is damaged by wetness during rainy seasons and causes suppurative crusts usually along the dorsum
- Cytology: long chains of branching cocci - classic “railroad track”. Gram positive cocci.
Dermatophilosis
- Weanling age horses
- Thickening of the small intestine and hypoproteinemia causing ventral edema clinically
- Lethargy, intermittent diarrhea, weight loss, and ventral edema
Lawsonia intracellularis
- Rickettsial agent: Ehrlichia risticii (recently named neorickettsia risticii)
- Obligate intracellular organism that survives in host machrophages
- Treatment Tetracyclines
- Diarrhea in the warmer summer months in horses stabled near bodies of water (vector is suspected)
- Acute onset of diarrhea, tachycardia,fever, lameness. Seasonal (warmer summer) diarrhea associated with laminitis.
- Treatment Oxytetracycline.
- Highly associated with laminitis.
Potomac Horse Fever
- Affects animals of 1 year or older
- Swelling of lymph nodes
- Can lead to guttural pouch empyema (less likely)
- Bastard Strangles: when Streptococcus equi s equi creates abscesses in unusual sites (other than LN)such as abdominal or lung lymph nodes
- Most sensitive diagnosis test: PCR o a guttural pouch wash for S. Equi Mproten (SeM( gene
- Culture is best performed on Columbia CNA agar.
- PCR more sensitive that culture. Serology best test for assessing exposure but no good tool to detect carriesrs.
Streptococcus equi subsp equi
- Most common infectious cause of infertility in US
- Common inhabitant of the external genitalia of mares and stallions
- Cause disease when predisposing factors (immunosuppression, pneumovagina, damage endometrium)
Streptococcus equi ssp. Zooepidemicus
- Equine piroplasmosis (Babesia caballi, Theileria equi)
- Fever, petechiations, signs consistent with hemolytic anemia
- Spread primarily by Ixodid ticks (or blood contamination), endemic in tropical,subtropical
- REPORTABLE in US
- Clinical infection: acute, chorionic or inapparent
- Acute clinical signs: lethargy,anorexia, pale or icteric mucous membranes - worsening disease: tachycardia, thachypnea, weakness, hemoglobinuria, weight loss, poor performance, partial anorexia
- Treatment: Imidocarb dipropionate and supportive care.
Babesia caballi
- Tyzzer’s disease. Acute necrotizing hepatitis.
- Motile filamentous, G(-), spore forming bacterium
- The rest of the clostridia organisms are categorized G(+)
- Depression, anorexia, coma, convulsions, jaundice
- Between 6 days and 6 weeks
- Elevated liver enzymes, marked hypoglycaemia and Acidosis
- Fever, icterus, acute diarrhea.
- Hyperfibrinogenemia, hypoglycemia and elevated liver enzymes.
Clostridium piliforme
- Leukocytosis, hyperfibrinogenemia and hyperglobulinemia
- Diagnosis: (horse with internal abscesses) Synergistic hemolysis inhibition test
Corynebacterium pseudotuberculosis
- Shaker Foal Syndrome
- Foals 2-6weeks susceptible to the toxicoinfectious form of botulism
- Toxin blocks the release of acetylcholine from the neuromuscular junction: flaccid paresis or paralysis
- Adult affected if infested performed toxin
- Dysphagia, weakness. Generalized muscle tremors, weak tongue tone and dilated, non-responsive pupils
- Flaccid paralysis, drooling, decreased muscle tone, weakness, dyspnea.
Clostridium botulinum
- Spore-forming bacteria G(-), rod shaped, obligate anaerobe.
- Enterocolitis and diarrhea adult horses and foals.
- Toxin A and Toxin B. Can survive prolong periods in the spore form.
- Transmission: oral-fecal route
- Risk factors: antibiotic and hospitalization
Clostridioides difficile
- Contagious equine metritis
Taylorella equigenitalis
- Often develop lockjaw, tongue do not hang out.
- Tetanus neurotoxin blocks post-synaptic inhibition to motor nerves.
- 3rd eyelid prolapse, oriented and erect ears, dyspnea, muscle spasms, quidding
Tetanus
- Theiler’s disease (adult horses)
- More in sheep and cattle.
- Acute serum hepatitis (Theiler’s disease)
- Acute lethargy, icterus, and hepatoencephalopathy
- Diagnosis: liver biopsy - Severe widespread hepatic necrosis, inflammatory cells.
- Mechanism unknown, type III hypersensitivity reaction
Clostridium novyi
- Isolation: (any 2 of 3) diarrhea, fever, neutropenia.
- Neutropenia is due to bacterial septicemia and endotoxemia due to GI disease
Salmonella
- Storm of abortions last trimester (7-11 months pregnancy)
- Foals: copious nasal discharge, recover over several weeks several months prior to an abortion storm classic for the virus
- Mares initially asymptomatic
- Transmitted - inhalation
- Equine herpesvirus - 1 (equine viral rhinopneumonitis)
- Rapidly - spreading / direct or indirect from infected nasal discharge, aborted fetuses or placenta
- Myeloencephalitis
- Main cause of paresis, abortions, and neonatal foal deaths
- Equine herpesvirus - 3 (equine coital exanthema)
- Spread venereally
- Papules, pustules, and ulcers on the vestibular mucosa, and vulvar skin, as well as the penis and prepuce (balanoposthitis). Less frequently affects the skin of the face. No systemic signs. Secondary bacterial infections are possible
- Sexual rest and appropriate sanititation of equipment are required to allow affected areas to heal and prevent transmission. Topical antibiotic may be warranted.
- Spontaneous recovery occurs over about 2 weeks
- EHV-1 and EHV-4
- Equine herpes myeloencephalopaathy: hind-limb paresis, bladder dysfunction, feel retention, xanthochromic (yellow) CSF.
- Vasculitis
Equine herpesvirus
- Transmitted by Culicoides
- Clinical signs typically develop 5-7 days after infection beginning wth fever and conjunctivitis
- Some animals recover
- Some animals develop pulmonary and/or cardiac form
- Pulmonary form: acute respiratory distress, coughing, sweating and foaming from nostrils. Form usually fatal
- Cardiac form: edema of the head and neck, abdominal pain,depression. Swelling in the indentation above the eyes (swelling of the supraorbital fossa)
- 50% animals with cardiac form die from heart failure
- Diagnosis: history of exposure, viral isolation and/or serology.
- No effective treatment. Control: vector control and vaccination.
African horse sickness
- Arterivirus, family Arteriviridae
- Transmitted venereally and by aerosol
- Vasculitis, leading to edema, conjunctivitis and LATE term abortion
Equine Viral Arteritis
- Affects horses, cattle and pigs
- High morbidity and low mortality
- Yearly outbreaks
- Vector: black flies and midges
- Affected migh be quarantined
- Sobering, not eating hay.
- Fever.
- Obvious oral ulcers on the tongue
- Reportable
- No specific treatment.
- Secondary infections.
Vesicular Stomatitis
- Transmitted by mosquito
- 27 different species of mosquito tat can transmit
- After inoculation, it spreads via the lymphatics.
- NEUROLOGIC signs until approximately 5 days post infection
- Cortical and thalamic lesions: head pressing, altered mentation, paresis, paralysis, convulsions, circling, ataxia and death (2-3 days after onset of clinical signs)
Eastern Equine Encephalomyelitis
- Progressive neurologic sings,
- No vaccines.
- Starting with anorexia and depression, hyperesthesia, propulsive walking and head tilt.
- CSF: CSF protein 75g/dL with mononuclear pleocytosis
Western Equine Encephalitis
- Flavivirus (mosquito born)
- clinical signs mild (Muscle fasiculations, slight ataxia) to severe (recumbency)
- Fever, lethargy, hind-limb ataxia, muscle fasiculations of face and neck.
-CSF: Clear color, Increased total protein. Increased Total Nucleated Cell Count. Cytology: Lymphocytic pleocytosis - Diagnosis: Serum IgM capture ELISA
West Nile Encephalitis
- Retrovirus genus lentivirus
- Weight loss, anemia and intermittent fevers
- Diagnosis: Immunodiffusion (Coggin’s test)
- Virus related with human immunodeficiency virus
- Treatment: isolation, and supportive care
- Transmission: blood-sucking flies
Equine Infectious Anemia
- Ringworm
- Multifocal lesions with alopecia and some crusting
- Around the head, neck and shoulders
Trichophyton equinum
Trichohyton equinum, T. Mentagrophytes, Microsporum gypsum
Sometimes: M. Canis, M equinum, and T. Verrucosum
Alopecia, crusting around saddle and girth regions
Diagnosis: Dermatophyte test media (DTM) or visualization of the fungal elements on KOH preps
Topical azole antifungals are most useful
A 2-year-old horse presents with intense pruritus around the tailhead and perineal region. The owner reports frequent tail rubbing, leading to hair loss and excoriation in these areas. Upon examination, yellowish-white egg masses are observed around the anus. What is the most likely diagnosis, and which diagnostic method would confirm the presence of the causative agent?
A. Oxyuris equi infection; perform a perianal tape test to identify eggs.
B. Strongyloides westeri infection; conduct a fecal flotation to detect larvae.
C. Habronema spp. infection; biopsy the skin lesions for histopathology.
D. Gasterophilus spp. infection; perform gastroscopy to visualize larvae.
Answer: A. Oxyuris equi infection; perform a perianal tape test to identify eggs.
Explanation: The clinical signs of intense pruritus around the tailhead, tail rubbing, and the presence of yellowish-white egg masses around the anus are characteristic of Oxyuris equi (equine pinworm) infection. Adult female pinworms migrate to the perianal region to deposit eggs, causing irritation and pruritus. A perianal tape test involves applying adhesive tape to the perianal area to collect eggs, which can then be examined microscopically for definitive diagnosis.
A herd of young horses, primarily under 18 months old, exhibits signs of tail rubbing and perineal irritation. The caretaker notes the presence of bare patches around the tail base in several animals. No significant abnormalities are found on fecal flotation tests. Considering the age group and clinical signs, which parasite is most likely responsible, and why might fecal flotation tests be inconclusive?
A. Oxyuris equi; eggs are deposited perianally, not typically present in feces.
B. Strongyloides westeri; larvae are transient in the intestines, making detection difficult.
C. Habronema spp.; eggs are too heavy to float in standard solutions.
D. Gasterophilus spp.; larvae reside in the stomach, not the intestines.
Answer: A. Oxyuris equi; eggs are deposited perianally, not typically present in feces.
Explanation: Oxyuris equi commonly affects horses less than 18 months old. The adult females migrate to the perianal region to lay eggs, leading to pruritus and tail rubbing. Because the eggs are deposited around the anus rather than being shed in the feces, fecal flotation tests often yield negative results. A perianal tape test is the preferred diagnostic method to detect O. equi eggs.
A horse diagnosed with Oxyuris equi infection has been treated with ivermectin, but the pruritus and tail rubbing persist. Further investigation reveals that other horses on the property are also affected. What is a plausible reason for the treatment failure, and what alternative anthelmintic class should be considered?
A. Resistance to macrocyclic lactones; consider using benzimidazoles.
B. Incorrect dosing; increase the ivermectin dosage.
C. Reinfection from the environment; implement strict hygiene measures.
D. Misdiagnosis; re-evaluate for other ectoparasites.
Answer: A. Resistance to macrocyclic lactones; consider using benzimidazoles.
Explanation:
There have been reports of Oxyuris equi developing resistance to macrocyclic lactones, such as ivermectin. Persistent clinical signs after treatment with ivermectin suggest potential resistance. In such cases, alternative anthelmintic classes, like benzimidazoles (e.g., fenbendazole or oxibendazole), may be more effective. Additionally, environmental management, including regular cleaning of stalls and paddocks to remove egg contamination, is crucial to prevent reinfectio