Emerging Infectious Diseases
Lecture 7 & Sample Questions
John L. Robertson
Emerging
Infectious Diseases in Horses: Serious Problems in the Past 25 Years
Sources
§
Equine Pathology, JR
Rooney and JL Robertson, ISU Press, 1996
§
The pathology of the
equine respiratory system JL Robertson and JR Rooney, 2nd Int. Equine Symp.
Proceedings, 1997
§
Publications from USDA
and State Depts. of Agriculture
§
Neuroimmunology of the
horse with special reference to EPM MO Furr, PhD thesis
Common causes of morbidity and mortality in
horses
§
Musculoskeletal
disease (many use-related
dysfunctions)
§
Digestive
catastrophes (colic)
§
Infectious diseases (neurologic and respiratory diseases most common)
Frequency of disease by anatomic location
§
Locomotor
system 52.2%
§
Skin 29.8%
§
Foot 12.7%
§
Eye 3.4%
§
Nervous
system 0.5%
Data from Prussian
Army horses (10 years)(1886-1895)
278,323 horses with illness
94.6% recovered
1.3% turned out
3.3% died
0.9%
killed
(Bartke, in Bayer-Frohner, 1900)
Common infectious diseases
§
Cardiovascular
- EVA, Streptococcus equi (zooepidemicus), Strongylus vulgaris
§
Respiratory
- influenza, EHV-1, S. equi, S. pneumoniae, R. equi, Dictyocaulus
arnfeldi
§
Digestive
- Salmonella sp., Ehrlichia risticii, Strongylus sp.
§
Reproductive
- EVA, EHV-1, Klebsiella genitalium
§
Nervous-
Arboviruses (many), rabies, EHV-1, Sarcocystis neurona
Diseases of antiquity
§
Strangles and other
respiratory diseases described by Greeks
Herbal preparations for therapy known in 1380 BC
§
Most modern diseases
(infectious and otherwise) described in German, Italian and French literature
before 1920
Factors favoring development of infectious
disease in horses
§
Cosmopolitan contact and
transportation
§
Altered host immunity
(iatrogenic, diet)
§
Altered age mix of
population
§
Husbandry systems
§
Novel vectors in novel
environments
§
New pathogens ?
Contagious equine metritis (CEM)
§
Transmissible venereal
disease of horses caused by Taylorella equigenitalis
§
Present in horses
worldwide
UK, France, Germany,
Ireland
§
First noted in US in
1977-78 in central Kentucky
§
Thoroughbreds more
seriously affected
Contagious equine metritis (CEM)
§
First case diagnosed in
UK in 1977
§
First cases diagnosed in
US in 1978 in Thoroughbred mares and 1979 in Missouri
§
Disease eradicated from
US
Contagious equine metritis (CEM)
§
Transmission
Natural sexual intercourse between
CEM infected horses and susceptible horses
Indirectly through artificial
insemination or fomites
An undetected carrier state in
stallions is important in propagating disease
Contagious equine metritis (CEM)
§
Clinical signs
Infertility / failure to conceive
Spontaneous abortion (rare)
§
In mares
Acute infection leads to vulvar
discharge
Chronic infection have less discharge
Carriers may be asymptomatic
Contagious equine metritis (CEM)
§
Lesions
Mild vulvar discharge
Mild to moderate suppurative
endometritis and myometritis
In chronic cases, mixed inflammatory
cell metritis
Few lesions in stallions
Contagious equine metritis (CEM)
§
Diagnosis
Bacterial culture
Serologic detection of antibodies
§
Treatment
Antibiotics and disinfectants
Rigid hygienic practices for breeding
§
Quarantine
has kept pathogen from US
Potomac horse fever (PHF)
§
Also known as equine
monocytic ehrlichiosis
§
Caused by infection with
Ehrlichia risticii
§
First seen as epizootic
in horses in Maryland and Virginia in 1979
Now seen in 32 states and Canada
Potomac horse fever (PHF)
§
Transmission
Precise mode of transmission is not known
Infectious organisms are found in feces
Seasonality of infection (late Spring and Summer)
suggests transmission via arthropods and reservoir hosts
A freshwater snail may be involved in the complex
transmission
Transplacental ?
Potomac horse fever (PHF)
§
Ehrlichia
risticii
Prefers to grow and sequester within monocytes (inside
vacuoles)
Shares antigenic determinants with E. sennetsu,
cause of human rickettsiosis in SE Asia
Variable morphology in different stages of disease
Potomac horse fever (PHF)
§
Clinical signs
Fever, anorexia and depression
Laminitis
Acute colitis (dorsal large colon)
with profuse diarrhea
Edema, hemoconcentration
Mortality of 10-30%
Potomac horse fever (PHF)
§
Lesions
Acute nonspecific mixed inflammatory
cell colitis
Acute laminitis
Difficult to differentiate from other
causes and presentations of colitis (Salmonella sp.)
Potomac horse fever (PHF)
§
Diagnosis
IFA, ELISA and PCR methods are available
Culture is difficult in cell free media (grows in
monocyte cultures)
§
Treatment
Generally symptomatic - antibiotics and fluids
§
Prevention
Bacterins are available
Equine protozoal myelitis
(EPM)
§
First described by
Rooney in 1970 as a focal myeloencephalitis in 52 horses with asymmetrical gait
and postural abnormalities
Equine protozoal myelitis
(EPM)
§
Caused by infection of
horses with Sarcocytis neurona
§
An intermediate host,
opposums, have been identified
§
Infection appears to
occur by consumption of contaminated food and water
Equine protozoal myelitis
(EPM)
§
EPM is
the most common cause of neurological dysfunction in horses
May affect (produce clinical disease) 1-3% of all
horses in US (esp. Warmbloods)
20 - 50% of horses have seroprevalence
60% of affected horses <4 years old
No apparent sex predilection
§
Seen in
North,Central and South America
Equine protozoal myelitis
(EPM)
§
Clinical signs
Restricted to CNS
Asymmetrical ataxia most common
Proprioceptive deficits
Spasticity and stumbling
Muscle atrophy
Equine protozoal myelitis
(EPM)
§
Lesions
Focal segmental hemorrhage
Necrosis of gray and white matter
Focal nonsuppurative
myeloencephalitis with lymphocytes, eosinophils and focal gliosis and neuronal
necrosis (micro)
Equine protozoal myelitis
(EPM)
§
Diagnosis
Immunoblot assay (Western blot) using
lysed cultured merozoites
PCR for protozoal DNA (KY and CA
variants)
CSF analysis - Albumin quotient:IgG
index
Equine protozoal myelitis
(EPM)
§
Treatment
Sulfonamide
antibiotics (sulfamethoxazole and trimethoprim) combined with pyrimethamine
have been the mainstay of current therapy
Diclazuril, and other
coccidiostats, have also been used but with variable results
Supportive therapy
On the horizon ...
§
A/equi/Jilin/1-89 -
equine influenza virus
§
Zoonotic paramyxoviruses
in Australia
Lecture 7 Sample Questions
1. A major factor which has
facilitated the development of emerging infectious diseases in horses is:
A. Worldwide transportation of horses
B. Decreased immunity in horses in general
C. Many new pathogens in the last 10 years
2. The most common type of disease or injury in horses, according to large
published studies is disease/lesions in what body system?
A. Urinary tract
B. Locomotor system
C. Respiratory system
3. The reason that contagious equine metritis is a problem in horses that have
it is:
A. It causes staggering and blindness
B. It causes lameness
C. It causes sterility and abortion
4. Published studies now indicate that equine protozoal myelitis:
A. Is a common infectious disease affecting the nervous system
B. Is a common disease which causes pneumonia
C. Is easily curable