1 - Infectious Diseases Flashcards
What is the etiology of equine strangles? Which horses does it typically infect?
Streptococcus equi ssp equi
Young horses mainly affected
How is strangles transmitted?
Direct and indirect nose/mouth contact or via contaminated fomites
How do horses become chronic carriers of strangles?
Chondroids may form in guttural pouch after infection, continue to carry infectious organism
Relative to disease course, when are horses shedding Strep equi? (disregarding chronic carriers)
Nasal shedding begins 4-7 days post infection, ceases 3-6 weeks after acute phase
What clinical signs are associated with strangles?
Depression/reduced appetite/fever precede nasal shedding
Serous then mucopurulent nasal discharge
Purulent lymphadenitis of the URT (LNs are firm and painful, rupture and drain ~1-2 weeks)
What complications are associated with strangles?
Asphyxiation Pneumonia (rare) Guttural pouch empyema Bastard strangle - dissemination and abscessation elsewhere Purpura hemorrhagica Immune-mediated myositis
How is strangles diagnosed?
Culture (S. equi NEVER commensal)
PCR (more sensitive)
Strep-M protein ELISA - for Bastard/purpura only
How is strangles treated in cases with early clinical signs and NO LN abscessation?
Procaine penicillin BID, NSAIDs
How is strangles treated in cases with abscessed LNs?
AVOID abx unless URT obstruction
Enhance maturation and drainage of LNs
What treatment can be given to horses exposed to strangles?
Penicillin may prevent disease
How is strangles treated in cases with complications?
Abx therapy for metastatic abscession
Local flushes in cases of pouch empyema
Penicillin and steroids for purpura
How are carriers identified in strangles cases?
Most horses stop shedding 4-6 weeks post-infection
Use nasal/GP washes (culture/PCR) to determine suitability to return to herd
If positive look for GP chondroids and retest q30 days
What vaccination options are there for strangles? What complications are associated with each?
- Killed (IM) - local swelling, injection site abscesses, purpura hemorrhagica
- Live attenuated (IN) - nasal discharge, lymphadenopathy, deep abscesses, limb edema, purpura
Which strains of equine herpesvirus are most important and which disease presentations do they cause?
EHV-1: abortion storms and EHM
EHV-4: rhinopneumonitis
Describe the rhinopneumonitis form of EHV.
Spread via aerosol, direct contact, fomites
Young animals most often affected
Signs (if any) 2-10 days post-exposure
Mostly upper respiratory signs (biphasic fever, nasal discharge, +/- cough, pharyngitis, tracheitis)
Recovery 2-3 weeks if no complications
Describe the abortive form of EHV.
Sporadic/storm abortions in last 4m of pregnancy
HIGH levels of virus in fetal fluids/placenta
Foals may be born alive but in bad shape
Mare’s future fertility not affected
Describe the myeloencephalopathy (EHM) form of EHV.
Gene mutation in viral DNA polymerase - more aggressive replication and higher risk of neuro disease
*Can occur in ANY strain of EHV
How is EHV diagnosed?
Must prove viremia + CS
1. Virus isolation and rtPCR - best choice
<10 days after infection, *nasal swabs + whole blood
2. CSF may show xanthochromia, RBCs, elevated protein
3. Serology with 4x rise in titer
4. Necropsy
5. Histopath - vasculitis, intranuclear inclusions
6. Immunohistochem on formalin-fixed tissue
How is EHV treated?
Symptomatic tx
Antivirals - Acyclovir IV or Valacyclovir PO
Neuro complications - NSAIDs, DMSO, corticosteroids
What isolation and quarantine protocols should be followed in EHV cases?
Isolate with >35 ft separation
Quarantine for 4 weeks after last case, 2 weeks if PCR test negative 2-4 times
Which drug can be used as an immunomodulator to reduce upper respiratory disease in EHV cases?
Zylexis
What vaccination options are there for EHV?
For herd control only:
Prestige II/V (killed for EHV-1/4)
Also indicated for pregnant mares:
Rhinomune (MLV for EHV-1)
Calvenza
Prodigy (killed for EHV-1)
For pregnant mares only:
Pneumabort K
What is the etiology of infectious bovine rhinotracheitis?
Bovine herpesvirus 1
How is IBR transmitted?
Inhalation, ingestion, and venereally
Virus is shed in respiratory, ocular, and genital secretions
What are the primary sites of infection of IBR?
Respiratory tract
Conjunctiva
Reproductive tract
Which strain of bovine herpesvirus causes encephalitis?
BHV - 5
How does IBR manifest in neonatal calves?
Pneumonia and gastroenteritis
What clinical signs are associated with standard IBR infection?
Cough, increased resp rate
Fever, inappetance
Nasal lesions (hyperemia)
What are the variant forms of IBR and what clinical signs do they have?
- Conjunctival form (Winter Pink Eye) - exudate of both eyes
- Urogenital form - focal pustular lesions
- Encephalitic form - calves under 6 months, generalized encephalitis
- Neonatal systemic form - calves infected late in gestation, severe respiratory and intestinal inflammation/necrosis
- Abortion - last trimester, retained placenta, autolyzed fetus
What necropsy findings are consistent with IBR? Standard, encephalitic, and neonatal systemic forms?
- Extensive respiratory diphtheric membrane
- Meningoencephalitis with intranuclear inclusion bodies
- Turkish towel lesion - entire forestomach has diphtheric membrane
How is IBR diagnosed?
Virus isolation by tissue culture
PCR
Viral Ag in immunofluorescence or IHC (post-mortem)
What are the differentials for abortion caused by IBR?
BVD
Lepto
Neospora
What are the differentials for conjunctivitis caused by IBR?
Bacterial keratoconjunctivitis
What are the differentials for neurologic dz caused by IBR?
Histophilus
Listeria
Rabies
toxic/metabolic dz
What are the differentials for neonatal dz caused by IBR?
FPT and bacterial septicemia
Neonatal diarrhea and septicemia
BVD
How is IBR treated and prevented?
Supportive care
Vaccination:
1. Killed vax (IM) - do not require refrigeration
2. MLV (IN) - approved in pregnant cows
3. MLV (IM) - may be approved in pregnant cows by label claims only
How long does passive (colostral) immunity for IBR last?
4-6 months (long!)
Which hosts does Bluetongue virus infect?
Cattle - natural hosts, rarely develop dz
Sheep - clinical disease
T/F: Bluetongue is a reportable virus.
TRUE (in many states)
What the pathogenesis of Bluetongue?
Infects endothelial cells
Widespread vasculitis
Edema and necrosis of epithelial and mucosal surfaces
What clinical signs are associated with Bluetongue?
SHEEP Edema of face, lips, muzzle, ears Serous to mucopurulent nasal discharge Oral erosions and ulcerations Coronitis and lameness/laminitis
Fetal infection disrupts organogenesis and causes teratogenesis, abortion, or weak lambs
How is Bluetongue diagnosed?
Viral isolation from blood/tissues (most definitive)
RT-PCR or serology
What are the ddx for oral lesions caused by bluetongue?
FMD
Vesicular stomatitis
Orf
Sheep pox
How is Bluetongue treated and controlled?
Supportive care
MLV vaccine
What is the etiology of Malignant Catarrhal Fever?
North American form - ovine herpesvirus 2
African form - alcelaphine herpesvirus 1 and 2
Which hosts does Malignant Catarrhal Fever affect?
No disease in natural hosts (sheep and wildebeest)
Highly fatal dz in non-host adapted ruminants (cattle)
What is the pathogenesis of Malignant Catarrhal Fever?
Replication in lymphoid tissue
Spread to endothelial cells throughout body
Widespread necrotizing vasculitis with lymphocytic cuffing
What clinical signs are consistent with Malignant Catarrhal Fever?
Keratoconjunctivitis, edema, ocular discharge
Mucopurulent nasal discharge
Oral ulcerations, salivation
Diarrhea, dysentery
Skin lesions of muzzle / teats and claws/horns may be sloughed
Progressive neurological signs
Death within 3-7 days
What are the ddx for Malignant Catarrhal Fever?
BVD / mucosal disease
Bluetongue (rare in cattle)
Vesicular stomatitis
FMD
T/F: Malignant Catarrhal Fever is reportable
False, but state/federal agencies should be notified d/t similarity to FMD
How is Malignant Catarrhal Fever diagnosed?
Viral isolation (nasal swabs, blood, PM tissues)
PCR (blood, PM tissues)
Serology
How is Malignant Catarrhal Fever treated?
Supportive care
Grave prognosis
What is the etiology/epidemiology of sporadic bovine lymphosarcoma?
Affects young cows. Etiology unknown
Describe calf/juvenile lymphosarcoma
Affects cattle under 1 year.
CS similar to adult enzootic form (generalized, symmetric lymphadenopathy)
Describe thymic (adolescent) lymphosarcoma
Affects cattle 6-24 months
CS are d/t space-occupying masses in the neck/thorax
Describe cutaneous lymphosarcoma
Affects cattle 1-3 years
Multiple raised, circular, ulcerated masses
What is the etiology/epidemiology of enzootic bovine lymphosarcoma?
Adult form (over 2 years), caused by bovine leucosis virus (BLV)
Transmitted horizontally by blood-sucking insects, direct contact with infected cattle, or iatrogenically
Low rate of vertical transmission transplacentally or by ingestion of milk/colostrum
What are the main CS associated with enzootic bovine lymphosarcoma?
Decreased milk production, weight loss, reduced appetite
External lymphadenopathy, internal abdominal lymphadenopathy
Abomasal/cardiac involvement
Exopthalmos
Posterior paresis/paralysis
How is enzootic bovine lymphosarcoma diagnosed?
CBC - lymphocytosis
*Histo or cytologic demonstration of neoplastic cells
Serology confirms BLV infection but not lymphosarcoma
How is enzootic bovine lymphosarcoma treated and controlled?
No tx recommended - 60 day prognosis
No vaccines
Serologic testing followed by
- Culling of all seropositive cattle
- Segregation of infected from uninfected cattle
- Control efforts to prevent further iatrogenic spread
T/F: Equine Herpes Myeloencephalopathy (EHM) is reportable
TRUE
T/F: BVDV is very stable in the environment and hard to disinfect
FALSE
How is BVDV transmitted?
Isolated in most body fluids
PI cattle and acutely infected cattle are major sources
Describe the standard pathogenesis of BVD
Primary replication in resp tract and tonsils
Dissemination to lymphoid tissue and epithelial surfaces
Lymphoid depletion and epithelial erosions
How does the pathogenesis of BVD occur in non-PI immunocompetent animals with NCP?
Replication is inhibited by immunity (passive or acquired), subclinical or mild infection most common
May cause infertility, acute disease, or thrombocytopenia
How does BVD occur in transplacental infection at 1-50 days of gestation?
Conception failure and early embryonic death
How does BVD occur in transplacental infection at 50-125 days of gestation?
Abortion and fetal mummification OR
immunotolerant PI calf
How does BVD occur in transplacental infection at 125-150 days of gestation?
Congenital abnormalities (cerebellar hypoplasia and ocular defects)
How does BVD occur in transplacental infection at 150-270 days of gestation?
Fetus mounts immune response (seropositive pre-colostrum) and clears virus OR
Virus causes organ damage leading to late term abortion
Describe the acute mucosal disease associated with BVD
Occurs in cases of superinfection (PI animals with NCP and CP)
Case fatality near 100% (5-7 days post-infection)
Depression, complete anorexia, rumen stasis, profuse watery diarrhea, oral lesions, skin erosions
Describe a case of acute BVD
Cattle 6-24 months
Erosive gastroenteritis and oral lesions
NOT typically fatal
Describe hemorrhagic/bleeder syndrome associated with BVD
Thrombocytopenia (under 25,000) and PLT dysfunction d/t viral infection of PLTs causing massive hemorrhage
Case fatality ~25%
Which form of BVD is the most common in endemic herds?
Reproductive disease
Infertility, repeat breeders, abortion, stillbirths, congenital abnormalities
Which form of BVD is typical of beef calves newly entering the feedlot?
Respiratory disease (d/t immunosuppressive effects of virus) Fibrinous pneumonia
What is the significance of getting pre-colostral titers for BVDV?
If calves are negative pre-colostrum, virtually no chance of PI animal in herd
Which diagnostic method for BVDV uses ear notch samples?
IHC staining for Ag
Useful to dx PI animals
Which two infectious diseases of cattle have long (~6 months) colostral protection?
IBR and BVD
How is BVD treated and prevented?
Abx and supportive therapy
MLV (IM) vaccine
Which leptospirosis serovars affect ruminants (esp cattle)
Hardjo - host adapted to cattle (long-term herd infections)
Pomona - cattle are incidental hosts
What clinical signs are associated with leptospirosis in ruminants?
Acute (lambs/calves) - hemolytic anemia
Subacute - drop in milk, slack udders, blood-stained milk, abortion (second half)
Chronic - transient milk drop followed by wave of abortions
How is leptospirosis in ruminants diagnosed? What diagnostic challenge is there?
Fluorescent Ab staining / PCR testing of urine
IHC or PCR of kidneys in aborted fetuses
Serology (MAT) - cannot use paired titers because already convalescent at time of abortion, use established serovar-based cutoffs
How is leptospirosis treated and prevented in ruminants
Cetiofur / oxytetracycline
Vaccination
Which leptospirosis serovars are significant in the equine?
Pomona and Bratislava
What clinical signs are associated with leptospirosis in horses?
Abortion
‘Moon blindness’ (recurrent uveitis/periodic opthalmia)
In foals - renal, hepatic, lung damage, hemolytic anemia
How is leptospirosis treated and prevented in the horse?
Abx - IV K penicillin, TMS, cephtiofur, tetracycline
For uveitis - Topical and systemic steroids, cyclosporine, NSAIDs
Vaccine available - new and not very efficacious
Which ruminant pathogen discussed can be isolated from NORMAL cattle?
Histophilus somni
Who does H. somni affect? When is it seen?
Feedlot cattle 4-12 months. Outbreaks ~4 weeks after arrival
Describe the pathogenesis of H. somni
Colonization of respiratory/urogenital mm
Pneumonia/endometritis
Septicemia and vasculitis
What clinical signs are associated with H. somni infection?
Pneumonia Septicemia (high fever and sudden death) TME (thrombotic meningioencephalitis) Myocarditis (exercise intolerance) Pericarditis (jugular distension and brisket edema) Pleuritis
How is H. somni diagnosed?
Primarily at necropsy
Serology - rapid seroconversion but titers fall rapidly
How is H. somni treated and prevented?
Most abx susceptible - ceftiofur and enrofloxacin DOC
Vaccines (bacterins) have many complications
Abx in feed during first 60 days on feedlot
*On arrival metaphylaxis effective for shipping fever but NOT H. somni
How is Mycoplasma bovis transmitted?
Ingestion of mastitic milk
Direct nose to nose contact
Aerosol of respiratory secretions
How does Mycoplasma bovis present clinically?
Mastitis
Pneumonia and polyarthritis
Otitis media/interna
What age of cattle are most susceptible to Mycoplasma bovis?
Calves
How is Mycoplasma bovis diagnosed?
Necropsy
IHC stains on histopath
Culture of M. bovis (M. spp is not significant)
How is Mycoplasma bovis treated and prevented?
Tulathromycin, enrofloxacin, gamithromycin, florfenicol
(Macrolides NOT effective, though good for most Mycoplasma)
Metaphylaxis on feedlots
How is Brucellosis (B. abortus) transmitted to humans?
Humans: -Unpasteurized dairy products (NOT in cooked meat) -Occupational exposures Cattle: -Ingestion -Semen
Describe the pathogenesis of B. abortus
Entry through mm of oral cavity, conjunctiva, skin, or nasal cavity
Localization in regional LN, proliferation
Bacteremia
How is B. abortus diagnosed?
Third trimester abortion w/o other clinical signs
Serology / culture
How is B. abortus controlled?
Vaccination
Surveillance by Market Cattle ID (blood sampling at slaughter) and Brucellosis Ring Test (milk)
What is the etiology of tuberculosis?
Mycobacterium bovis
How is tuberculosis transmitted?
Bronchial secretions, milk, meat
Describe the pathogenesis of tuberculosis
Primary focus at point of infection (lung/intestine)
Calcification of focus and regional LNs
Enlarging lesion and metastatic spread
How is tuberculosis diagnosed and monitored?
Intra-dermal caudal fold test (CFT)
