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Veterinary Year 3 > Infectious Diseases of Horses > Flashcards

Infectious Diseases of Horses Flashcards

1
Q

Describe the general features of Salmonella enterica

A
  • gram -ve rod shaped bacteria
  • facultative anaerobe
  • facultatively intracellular - persists in macrophages evading immune detection
  • opportunistic pathogen
  • zoonotic
  • can survive well in the environment
  • spread by direct contact with faeces or fomites
  • recovered animals can shed for a number of weeks
  • produces 3 exotoxins which cause diarrhoea through causing a significant inflammatory response
  • results in inflammation and necrosis of the gut lining causing leakage of fluid and proteins resulting in diarrhoea
  • Also releases endotoxin LPS which triggers a neutrophil dominated inflammatory response
  • clinical signs include: diarrhoea, depression, dehydration and in severe cases endotoxaemia
  • diagnosis via faecal culture - isolate until 5 samples in 24 hours are negative
  • High antimicrobial resistance
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2
Q

Describe the general features of acute colitis

A
  • costridium perfringens and difficile = 2 main pathogenic causes
  • usually part of normal gut flora
  • large, endospore forming, gram +ve rod shaped bacteria
  • obligate anaerobes
  • requires a change in the gut to cause disease
  • clinical signs include: colic, depression, diarrhoea
  • culture is unreliable for diagnosis due to gut flora status, look for enterotoxins using an ELISA
  • high mortality
  • resistant to many disinfectants and temperature extremes
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3
Q

Describe the general features of rotavirus

A
  • virus transmitted by ingestion of contaminated faecal matter or fomites
  • resistant to bleach
  • most common cause of equine infectious diarrhoea in foals less than 2 months
  • 18-24 hour incubation
  • affects absorptive epithelium on villi causing atrophy leading to poor nutrient absorption and osmotic diarrhoea and can result in haemorrhage and necrosis
  • self-limiting; lasts 5-7 days
  • very infectious
  • infected animals shed for 2 weeks post recovery
  • vaccine available for the mare to be given at 8th, 9th and 10th month of each pregnancy
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4
Q

Describe the general features of pathogenic clostridium species

A
  • gram positive
  • part of the normal gut flora
  • opportunistic pathogens
  • anaerobic
  • C.perfringens is non-motile, type A most common pathogen
  • C. difficile is motile and produces toxin A which kills macrophages and is pro-inflammatory
  • high mortality
  • form environmentally stable spores, resistant to many disinfectants
  • diagnosis via ID of toxins via an ELISA
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5
Q

What factors increase likelihood of horses contracting GI diseases?

A 
stress
surgery
transport
hospitalisation
feed change
anthelmintic treatment 
Antibiotics and some other medications
contact with new horse herds - low biosecurity
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6
Q

Describe the general features of viral pappilomas

A
  • commonly known as grass warts
  • papilloma virus
  • mainly seen in young horses
  • see pinky grey lesions around the face, muzzle, lips and genitals
  • cause no discomfort
  • spontaneous resolution, no treatment necessary
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7
Q

Describe the general features of horse pox

A
  • very rare
  • pox virus
  • 2 forms exist - buccal and cutaneous forms
  • see systemic signs: mild fever and depession
  • spontaneous resolution, no treatment necessary
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8
Q

Describe the general features of pinnal acanthosis

A
  • commonly known as aural plaques
  • papilloma virus
  • transmitted by black flies (simulium)
  • no need to treat, can cause head shyness
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9
Q

Describe the general features of sarcoids

A
  • most common equine skin tumour
  • tumour of fibrobasts
  • horses have a genetic predisposition
  • spread by flies
  • are histologically distinctive but can become aggressive post biopsy
  • 6 types:
    1. occult
    2. verrucose
    3. nodular
    4. fibrobllastic
    5. mixed
    6. Malignant
  • various treatments available depending on size, type and location of the sarcoid
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10
Q

Describe the general features of papular dermatosis

A
  • rare in the UK
  • caused by the pox virus
  • causes papular lesions on the skin
  • causes no discomfort
  • spontaneous resolution in 4-6 weeks
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11
Q

Describe the general features of coital exanthema

A
  • caused by equine herpes virus 3
  • transmitted via iinhalation of droplets of via direct contact
  • has a 5-7 day incubation
  • only significant in breeding animals
  • good immunity post-infection
  • causes rapidly developing mildly pruritic papules in the genital region
  • healing papules can leave a permanent depigmentation of the skin
  • stop breeding until 3 weeks after the papules have fully healed
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12
Q

Describe the general features of dermatophytosis

A 
- commonly known as ring worm
2-3 week incubation
- some immunity gained with age
- causes small circular patches of hair, accumulation of keratin and bald patches
- heal from the centre outwards
- self limiting, clears in 5-10 weeks 
- highly contagious
- can treat with miconazole
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13
Q

Describe the general features of dermatophilosis

A
  • commonly known as rain scald
  • caused by dermatophilus congolensis, a ram positive bacteria
  • affects areas regularly soaked with water
  • mildly painful, causes matted clumps of hair with a crusting purulent base
  • treat by covering to protect against rain or moving to a dry environment, bathe with antimicrobial washes and remove crusts
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14
Q

Describe the general features of streptococcal dermatitis

A
  • gram positive organisms
  • strep equi equi is an obligate pathogen which causes bastard strangles which results in abscesses throughout the body, causing respiratory signs and affects the guttural pouches
  • strep equi zooepidemicus is an opportunistic pathogen causing cellulitis, furniculitis and folliculitis. Mildly painful lesions
  • treat with topical antimicrobial creams and washes, responsive to penicillin, can give systemically in severe cases
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15
Q

Describe the general features of staphylococcal dermatitis

A
  • gram positive
  • most common agents : staph aureus and staph intermedius
  • this causes painful, exudative, localised dermatitis, abscesses and pyogranulomas
  • commonly secondary to trauma
  • resistant to many antimicrobials
  • causes saddle rash and pastern folliculitis (mud fever)
  • treat by clipping the infected area, using antiseptic washes, draining any abscesses and give systemic antimicrobials based on culture and sensitivity
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16
Q

Describe the general features of equine herpes virus including isigns, diagnosis and treatment

A
  • EHV1 is responsible for causing neurological problems
  • clinical signs are a result of vasculitis and thrombosis of arterioles in the brain and spinal cord: pyrexia, sudden onset, ataxia, atony of the bladder, flaccid tail and anus
  • prior to neurological signs there may have been respiratory signs or abortion linked to herpes virus
  • virus can be isolated from a CSF sample or via a nasal swab
  • very long recovery process
  • isolate from other horses, if recumbent prognosis is poorer as requires much more nursing
    aspirin, corticosteroids and NSAIDs can be given to reduce swelling
    A vaccine is available for EHV 1 and 4 but is not effective against the neurological strain
17
Q

What are the herpes viruses and what conditions do they cause in the horse?

A 
• EHV-1: respiratory,
abortion,
myeloencephalopathy
• EHV-2: keratitis
• EHV-3: coital exanthema
• EHV-4: respiratory
• EHV-5: multinodular
pulmonary fibrosis
• EHV-6 to 8: donkeys
18
Q

Describe the general features of Rabies

A
  • Lyssavirus
  • neurotrophic
  • transmitted in saliva, obtained via being bitten by an infected animals
  • zoonotic
  • rare in horses
  • pathogenesis: from point of infection the virus accesses the peripheral nervous system and tracks up to the central nervous system where is replicates in the spinal and dosal root ganglia. It then spreads back down the other nerves and accesses the salivary glands
  • has an incredibly varied incubation but is inevitably fatal
    difficult to diagnose due to vague signs but on histopath see eosinophylic inclusion bodies (negri bodies) in the brain or can diagnose by doing a fluorescent antibody test

no treatment, euthanasia required

19
Q

Describe the different forms of rabies and their clinical signs

A

Spinal or paralytic form - most common in horses:
local hyperalgesia and self mutilation and progressive ascending ataxia, weakness and lameness

brain stem or dumb form - uncommon in horses:
• Depression
• Anorexia
• Head tilt / circling
• Ataxia
• Dementia / Blindness
• Salivation / Dysphagia
• Tail / Penis / Bladder paralysis
• Self-mutilation
Cerebrum or furious form - uncommon in horses:
• Photophobia / Hydrophobia
• Aggression / Bizarre behaviour
• Hyperaestheisa
• Tenesmus
• Muscle tremors
• Seizures
20
Q

describe the general features of west Nile virus

A 
flavivirus
birds act as a reservoir
transmitted by mosquitoes
causes fever, depression and anorexia
causes multi-focal encephalomyelitis 
neurological symptoms include: – Muscle fasciculations over entire body
(particularly head and neck)
– Weakness, ataxia, dysmetria
– Cranial nerves may be affected
– Mentation may be affected (indirectly due to
intracranial oedema)
– Sudden death in some horses
- treat with hyperimmune plasma and supportive care with NSAIDs, corticosteroids and mannitol to reduce oedema
21
Q

Name the viral causes of respiratory disease in horses

A
  • Adenovirus
  • Influenza
  • Equine herpes viruses 1&4
  • Rhinovirus
  • Equine viral arteritis - notifiable
  • African Horse sickness - notifiable
22
Q

Describe the general features of adenovirus

A

causes mild or sub-clinical disease only a problem in Arab foals with severe combined immunodeficiency syndrome

23
Q

Describe the general features of influenza

A
  • orthomyxovirus with sub-types based on the H and N surface glycoproteins
    public health concern
  • spread via inhalation
  • virus attaches to the respiratory mucosa cells and inhibits the mucocilliary apparatus, it then spreads throughout the respiratory tract
  • damage and impairment of the respiratory epithelium gives rise to secondary infections
  • younger horses at higher risk
  • subclinical carriers shed the virus into the environment
  • high morbidity, low mortality
  • short incubation of 24-48 hours
  • clinical signs: pyrexia, nasal discharge ( watery then changing to mucopurulent, Coughing, tachypnea, inappetance,
    retropharyngeal lymphadenopathy and weight
    loss
  • symptoms usually last 7-14 days

Veterinary Year 3 (12 decks)

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