African Horse Sickness

1
African Horse Sickness

• Perdesiekte,
• Pestis Equorum,
• La Peste Equina,
• Peste Equina Africana

2
Overview

• Etiology
• Species Affected
• Epidemiology
• Economic Importance
• Clinical Signs
• Diagnosis and Treatment
• Prevention and Control
• Actions to Take

3
Etiology
4
African Horse Sickness Virus

• Non-enveloped RNA
• Family Reoviridae
• Genus Orbivirus
• Nine serotypes (1-9)
• All viscerotropic
• Serotype 9
• Endemic areas
• Outbreaks outside of Africa
• Serotypes 1-8
• Limited geographical areas

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African Horse Sickness Virus

• Inactivated by
• Heat (temps greater than 140oF)
• pH less than 6, or 12 or greater
• Acidic disinfectants
• Rapidly destroyed in carcasses that have
  undergone rigor mortis

6
Epidemiology
7
Species Affected

• Equidae
• Horses, donkeys, mules
• Zebras
• Other
• Camels
• Dogs

8
Geographic Distribution

• Endemic in sub-Saharan Africa
• Outbreaks
• Southern and northern Africa
• Near and Middle East
• Spain and Portugal

9
OIE Disease Distribution Map
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Incidence/Prevalence

• Seasonal
• Late summer - early autumn
• Cyclic
• Drought followed by heavy rains
• Influences insect breeding
• Epizootics halted by
• Frost
• Lack of long-term vertebrate reservoir
• Reduced numbers of vectors
• Control measures
• Vaccination, vector abatement

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Morbidity/Mortality

• Varies with species, previous immunity, form of
  disease
• Mortality based on species
• Horse particularly susceptible

Species Mortality
Horses 50-95
Mules 50
European and Asian donkeys 5-10
African donkeys and zebras Rare
12
Morbidity/Mortality

• Mortality based on form of disease

Disease Form Mortality
Pulmonary form Up to 95
Cardiac form 50 or more
Mixed form 70-80
Horsesickness fever Typically recover
13
Transmission
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Transmission

• Not contagious
• Vector-borne Culicoides spp.
• Culicoides imicola principal vector
• C. bolitinos
• C. variipennis
• Other potential arthropods
• Viremia in Equidae
• Horses 12 to 40 days
• Zebras, African donkeys up to 6 weeks

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Culicoides spp.

• Biting midges, punkies, no-see-ums
• Extremely small 1/8
• Species identified by wing pattern
• Habitat
• Margins of water sources
• Life cycle 2-6 weeks
• Eggs hatch in 2-10 days
• Females are bloodsucking
• Greatest biting activity dusk to dawn

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Economic importance
17
History

• 1600 First recorded
• Horses to southern Africa
• 1921 Sir Arnold Theiler
• Described 7 major epizootics in South Africa
  from 1780-1918
• 1959-61 Middle East
• 1st outbreak outside Africa
• 1987-91 Spain, Portugal
• Imported zebra reservoirs
• New Culicoides species

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Economic Impact

• 1989 Portugal
• 137 outbreaks
• 104 farms
• 206 equines destroyed
• 170,000 equinesvaccinated
• Cost 1.9 million

SPAIN
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U.S. Economic Impact

• U.S. Horse Industry (2007)
• Inventory 4 million horses
• Sales 2.0 billion
• Employment 4.6 million Americans
• Risk factors
• Disease not in U.S. naïve population
• Arthropod vector is in U.S.
• Outbreak would result in movement and trade
  restrictions

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African Horse Sickness in Animals
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Incubation Period

• Experimental 2-21 days
• Natural infection 3-14 days

Disease Form Incubation Period
Peracute (pulmonary) form 3-5 days
Subacute (edematous or cardiac) form 7-14 days
Acute (mixed) form 5-7 days
Horsesickness fever 5-14 days
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Clinical Signs

• Four forms of the disease
• Peracute (pulmonary)
• Subacute edematous (cardiac)
• Acute (mixed)
• Horsesickness fever
• Symptomatic infections most common in horse and
  mules
• Zebras typically asymptomatic

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Peracute - Pulmonary Form

• Acute fever
• Sudden, severerespiratory distress
• Dyspnea, tachypnea
• Profuse sweating
• Spasmodic coughing
• Frothy serofibrinous nasal exudate
• Rapid death (few hours)

Foam from the nares due to pulmonary edema
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Subacute Edematous - Cardiac Form

• Edema
• Supraorbital fossae, eyelids
• Cheeks, lips, tongue, intermandibular space
• Neck, thorax, chest
• Not in lower legs
• If animal recovers, swellings subsideover 3-8
  days

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Subacute - Cardiac Form

• Terminal stages
• Severe depression, colic, petechiae of
  conjunctivae and ventral tongue
• Death from cardiac failure
• Mortality 50 or higher
• Death within 4-8 days

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Acute - Mixed Form

• Pulmonary and cardiac forms
• Cardiac signs usually subclinical
• Followed by severe respiratory distress
• Mild respiratory signs
• Followed by edema and death
• Diagnosed by necropsy
• Mortality 70-80

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Horsesickness Fever

• Mild clinical signs
• Characteristic fever (3 to 8 days)
• Morning remission (undetectable)
• Afternoon exacerbation
• Other signs
• Mild anorexia or depression
• Congested mucous membranes
• Increased heart rate
• Rarely fatal

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Post Mortem Lesions

• Pulmonary form
• Severe, diffusepulmonary edema
• Hydrothorax
• Fluid in abdominal and thoracic cavity
• Enlarged endematous lymph nodes
• Hyperemia and petechial hemorrhages in intestines

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Post Mortem Lesions

• Cardiac form
• Yellow gelatinous infiltrate
• Head, neck, shoulders
• Brisket, ventral abdomen, rump
• Hydropericardium
• Submucosal edema of cecum, large colon, rectum
• Mixed form
• Mixture of above findings

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AHS in Other Species

• Dogs
• Ingestion of infected horse meat
• Not usually by insect bites
• No role in spread or maintenance
• Dogs usually have the pulmonary form
• Camels, zebras
• Inapparent infection

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Diagnosis and Treatment
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Differential Diagnosis

• Equine viral arteritis
• Equine infectious anemia
• Hendra virus infection
• Purpura hemorrhagica
• Equine piroplasmosis
• Equine encephalosis virus
• Anthrax
• Toxins

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Diagnosis

• Clinical signs
• Supraorbital swelling is characteristic
• History
• Prevalence or exposure to competent vectors
• Travel from enzootic area
• Laboratory tests - definitive diagnosis
• Serotype needed for control measures

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Laboratory Diagnosis

• Laboratory tests
• Virus isolation
• ELISA, RT-PCR
• Serology (tentative)
• Necropsy spleen, lung, lymph node
• More than one test should be used
• AHSV does not cross-react with other known
  orbiviruses

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Sampling

• Before collecting or sending any samples, the
  proper authorities should be contacted.
• Samples should only be sent under secure
  conditions and to authorized laboratories to
  prevent the spread of the disease.

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Samples To Collect

• For virus isolation
• Blood samples
• Necropsy samples
• Spleen, lung, lymph nodes
• Paired serum samples are recommended
• Store and transport samples at 39oF

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African Horse Sickness in Humans
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AHS in Humans

• No natural infection in humans
• Neurotropic vaccine strains
• Transnasal infection can lead to encephalitis or
  retinitis
• Handle modified live AHS vaccine strains with
  caution

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Prevention and Control
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Recommended Actions

• IMMEDIATELY notify authorities
• OIE reportable disease
• In the U.S. notify
• Federal Area Veterinarian in Charge (AVIC)
  www.aphis.usda.gov/animal_health/area_offices/
• State Veterinarian www.usaha.org/Portals/6/StateAn
  imalHealthOfficials.pdf
• Quarantine premises

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Disinfection

• Disinfectants
• Sodium hypochlorite (bleach)
• 2 acetic or citric acid
• Killed
• pH less than 6
• pH 12 or greater
• Rapidly destroyed in carcasses that have
  undergone rigor mortis

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Control

• Quarantine
• Equidae from endemic areas
• Asia, Africa, Mediterranean
• Minimum 60 days at point of entry
• Vector control and protection
• Insect repellants
• Stable in insect-proof housingfrom dusk to dawn

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Control

• Monitor temperature of all equids
• If febrile
• Euthanize or isolate in an insect-free stable
  until cause is determined
• Vaccination
• In endemic areas
• Surrounding protection zone
• Not available in the U.S.

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Vaccination

• Attenuated live vaccine available
• Horses, mules, donkeys
• Not in U.S.
• Reassortment possible
• Teratogenic
• No killed or subunit vaccine available
• Recovering animals
• Lifelong immunity post-infection to the
  infecting serotype

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Additional Resources

• World Organization for Animal Health (OIE)
• www.oie.int
• Center for Food Security and Public Health
• www.cfsph.iastate.edu
• USAHA Foreign Animal Diseases (The Gray Book)
• www.aphis.usda.gov/emergency_response/downloads/n
  ahems/fad.pdf
• Center for Infectious Disease Research and Policy
• www.cidrap.umn.edu/cidrap/content/biosecurity/ag-b
  iosec/anim-disease/ahs.htm
• African Horse Sickness Trust
• www.africanhorsesickness.co.za

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Acknowledgments

• Development of this presentation was made
  possible through grants provided to the Center
  for Food Security and Public Health at Iowa State
  University, College of Veterinary Medicine from
• the Centers for Disease Control and Prevention,
  the U.S. Department of Agriculture, the Iowa
  Homeland Security and Emergency Management
  Division, and the Multi-State Partnership for
  Security in Agriculture.
• Authors Glenda Dvorak, DVM, MPH, DACVPM Anna
  Rovid Spickler, DVM, PhD
• Reviewers James A. Roth, DVM, PhD Bindy Comito,
  BA Katie Spaulding, BS Meghan Blankenship, BS
  Kerry Leedom Larson, DVM, MPH, PhD, DACVPM