African Horse Sickness Texas A&M University Texas A&M University College of Veterinary...

African Horse Sickness African Horse Sickness

Texas A&M University Texas A&M University College of Veterinary MedicineCollege of Veterinary Medicine

Jeffrey Musser, DVM, PhD, DABVP Jeffrey Musser, DVM, PhD, DABVP

Suzanne Burnham, DVMSuzanne Burnham, DVM

20062006

African Horse SicknessAfrican Horse Sickness

African horse sickness (AHS) is African horse sickness (AHS) is an infectious but an infectious but noncontagious, insect-borne noncontagious, insect-borne viral disease affecting all viral disease affecting all species of equids. species of equids.

It is transmitted in the field by It is transmitted in the field by at least two species of at least two species of CulicoidesCulicoides..

It is characterized by clinical signs and It is characterized by clinical signs and lesions associated with respiratory and lesions associated with respiratory and circulatory impairment.circulatory impairment.

Horses will be seen standing with their legs Horses will be seen standing with their legs apart and their head extended.apart and their head extended.

African Horse Sickness is an OIE reportable disease. African Horse Sickness is an OIE reportable disease.

www.hedweb.com/animalag/horsesw.htm

“If you hear hoof beats, look for horses….

http://

But don’t forget to look for zebras too!

http://www.singerhuette.at/Afrika/Serengeti%202%202003.htm

Disease reported present

Disease reported absent

Data unavailable or incomplete

African Horse Sickness in the World in 2004. OIE

http://www.oie.int/eng/info/en_presdistribgeo.htm

EtiologyEtiology

Host rangeHost range

Incubation Incubation

Clinical signsClinical signs

TransmissionTransmission

Diagnosis Diagnosis

Differential DiagnosisDifferential Diagnosis

EtiologyEtiology

African Horse Sickness is caused by African Horse Sickness is caused by an Orbivirus of the family an Orbivirus of the family ReoviridaeReoviridae

Family: Reoviridae Family: Reoviridae Genus: Genus: OrbivirusOrbivirus Nine different serotypes of the virus Nine different serotypes of the virus have been describedhave been describedA viscerotropic virusA viscerotropic virus

SerotypesSerotypesAll serotypes of AHS All serotypes of AHS virus occur in eastern virus occur in eastern and southern Africa; and southern Africa; this distribution this distribution reflects the geographic reflects the geographic pattern of zebra, which pattern of zebra, which cycle the virus cycle the virus asymptomatically and asymptomatically and probably serve as a probably serve as a reservoir for the virus. reservoir for the virus.

SerotypesSerotypes

Only African Horse Only African Horse Sickness virus Sickness virus serotype 9 is found in serotype 9 is found in West Africa where West Africa where zebra do not occur. zebra do not occur.

SerotypesSerotypesPeriodically, AHS Periodically, AHS virus spreads beyond virus spreads beyond sub-Saharan Africa sub-Saharan Africa and the disease has and the disease has caused major caused major epizootics extending epizootics extending as far as Pakistan and as far as Pakistan and India in the east and India in the east and Morocco, Spain and Morocco, Spain and Portugal in the WestPortugal in the West. .

Host RangeHost Range

HorsesHorses MulesMules DonkeysDonkeys ZebrasZebras

In order of decreasing severity of disease:In order of decreasing severity of disease:

Approximately Approximately

70-95 % of all horses 70-95 % of all horses

developing the disease will diedeveloping the disease will die

yet the mortality percentage for yet the mortality percentage for

mules is only about 50 percent mules is only about 50 percent

and for donkeys only 10 percent.and for donkeys only 10 percent.

Role of ZebrasRole of Zebras

AHS virus over-AHS virus over-winters in zebras winters in zebras in Kruger National in Kruger National Park, from where Park, from where it spreads it spreads westwards and westwards and southwards every southwards every year.year.

Image courtesy of Dr Corrie Brown

ZebrasZebras

AHS remains AHS remains endemic in zebra endemic in zebra populations across populations across South AfricaSouth Africa

They harbor the virus They harbor the virus and are often the and are often the source of sudden source of sudden outbreaks in Africaoutbreaks in Africa

Host Range Host Range

Dogs can also become infected by Dogs can also become infected by eating infected meat.eating infected meat.

1987-90 outbreak in Spain:1987-90 outbreak in Spain:

Dogs that did not consume infected Dogs that did not consume infected meat were found to be seropositive, meat were found to be seropositive, suggesting infection by arthropod suggesting infection by arthropod bites. bites.

Dogs infected with this virus may Dogs infected with this virus may have the pulmonary form of the have the pulmonary form of the disease.disease.

In a survey in Egypt, antibodies to In a survey in Egypt, antibodies to AHS virus were detected in sheep, AHS virus were detected in sheep, goats, camels, buffalo and dogs.goats, camels, buffalo and dogs.

Host RangeHost Range

There is no evidence that humans can be There is no evidence that humans can be infected by field strains of the disease. infected by field strains of the disease. However, intranasal exposure to However, intranasal exposure to neurotrophic vaccine strains has caused neurotrophic vaccine strains has caused encephalitis and retinitis in humans.encephalitis and retinitis in humans.

IncubationIncubation

In experiments, African Horse Sickness In experiments, African Horse Sickness usually has a 5 to 7 day incubation usually has a 5 to 7 day incubation period.period.

In natural infections, circumstantial In natural infections, circumstantial evidence indicates that the incubation evidence indicates that the incubation period is from 7 to 14 days. period is from 7 to 14 days.

Clinical SignsClinical Signs

Infected horses remain viremic for Infected horses remain viremic for approximately 18 days, although the fever approximately 18 days, although the fever may be present for another 4 to 8 days, if may be present for another 4 to 8 days, if the animal should live that long. Despite the animal should live that long. Despite their reduced mortality, the viremic stage their reduced mortality, the viremic stage in donkeys may last for up to 28 days. in donkeys may last for up to 28 days. Zebras appear to be very similar to Zebras appear to be very similar to donkeys in this regard.donkeys in this regard.

First Sign:First Sign:

Fever of 102Fever of 102°F°F to to 106106°F, °F,

(38.9°C - 41.1°C)(38.9°C - 41.1°C)

Most Common SignMost Common Sign

Congestion of the Congestion of the conjunctivaeconjunctivae

Severity of Severity of congestion is good congestion is good indication of indication of severity of severity of infectioninfection

Lower Eyelid ConjunctivitisLower Eyelid Conjunctivitis

After initial signs, the disease can progress in one of four ways:

Peripheral (Cardiac) called “Dikkop” in S. Africa

Central (Pulmonary) called “Dunkop” in S. Africa

Mixed Form (Acute) Mixed Form (Fever)

Clinical Signs: Clinical Signs: PulmonaryPulmonary Fever up to 104Fever up to 104°F°F

to 106to 106°F°F Increasingly more Increasingly more

rapid respiration rapid respiration and abdominal and abdominal expirationexpiration Respiratory rate may Respiratory rate may

reach 60-70 per reach 60-70 per minuteminute

Coughing and Coughing and SweatingSweating

http://www.vet.ed.ac.uk/animalpain/Pages/images/Optimised%20Images/optphotos/EQsweating.jpg

Clinical Signs: PulmonaryClinical Signs: Pulmonary

Horse may appear Horse may appear colicky (getting up colicky (getting up and down, and and down, and rolling)rolling)

As pulmonary As pulmonary distress increases:distress increases:

Animal stands with Animal stands with forelegs apartforelegs apart

Head extendedHead extended

Nostrils dilatedNostrils dilated

Once foam Once foam appears appears in nostrils, in nostrils, death death follows rapidly.follows rapidly.

Animal may drink and eat, even in terminal stages.Animal may drink and eat, even in terminal stages.

African Horse SicknessAfrican Horse SicknessPhoto courtesy of Plum Island

In my few encounters with the disease, I was In my few encounters with the disease, I was struck by the extreme struck by the extreme

respiratory distress including froth pouring from the respiratory distress including froth pouring from the nostrils, nostrils,

extensive hydrothorax and hydropericaridium, extensive hydrothorax and hydropericaridium, supraorbital edema and a supraorbital edema and a

gelatinous infiltration of subcutaneous tissue and gelatinous infiltration of subcutaneous tissue and intermuscular intermuscular

fascial planes along the ligamentum nuchae and fascial planes along the ligamentum nuchae and muscles of the muscles of the

shoulder. shoulder. Dr Botlhe ModisaneDr Botlhe Modisane 20062006

In 2004, South Africa reported 196 outbreaks In 2004, South Africa reported 196 outbreaks resulting in 335 cases resulting in 335 cases

and 166 deaths. The case fatality rate was even and 166 deaths. The case fatality rate was even higher in 2003, with higher in 2003, with

89 outbreaks resulting in 510 cases and 441 89 outbreaks resulting in 510 cases and 441 deaths. Prior to this deaths. Prior to this

outbreak, the Western Cape province had been outbreak, the Western Cape province had been declared an AHS-free declared an AHS-free

zone from which horses could be exported. - zone from which horses could be exported. - Mod.PC]Mod.PC]

Clinical Signs: CardiacClinical Signs: Cardiac

Incubation is usually longer (7-14 days)Incubation is usually longer (7-14 days)

Fever of 102-106Fever of 102-106°F usually lasts 3-6 °F usually lasts 3-6 daysdays

Clinical Signs: Cardiac Clinical Signs: Cardiac

At the end of the febrile At the end of the febrile period, marked period, marked swelling of the head swelling of the head and neck may occurand neck may occur

Clinical Signs: Cardiac Clinical Signs: Cardiac

Classic areas for swelling Classic areas for swelling are:are:

Supraorbital fossaSupraorbital fossa

ConjunctivaConjunctiva

Lips, cheeks, tongueLips, cheeks, tongue

Intermandibular spaceIntermandibular space

Laryngeal areaLaryngeal area

Neck, brisket, ventral Neck, brisket, ventral thoraxthorax

http://www.spc.int/rahs/Manual/images/AfrHorsSick-09.jpg

Peri-orbital swellingPeri-orbital swelling

No edema of the lower parts of the legs No edema of the lower parts of the legs occursoccurs

Petechial hemorrhages on the ventral Petechial hemorrhages on the ventral surface of the tongue and in conjunctiva surface of the tongue and in conjunctiva may occurmay occur

As edema progresses, there may be As edema progresses, there may be restlessness and signs of abdominal pain restlessness and signs of abdominal pain and pulmonary edemaand pulmonary edema

Finally, Finally, animal animal becomes becomes prostrate, prostrate, and diesand dies

Again, Again, animal may animal may eat and eat and drink, even in drink, even in terminalterminal stagesstages

http://www.usyd.edu.au/su/rirdc/articles/disease/ahs.jpg

http://www.vet.uga.edu/vpp/IVM/ENG/Modes/definition03.htm

Recovery: CardiacRecovery: Cardiac

If the disease is not fatal, the edema If the disease is not fatal, the edema will subside over 3 to 8 days.will subside over 3 to 8 days.

Clinical Signs: Mixed Form Clinical Signs: Mixed Form (acute)(acute)

Mixture of pulmonary and cardiac Mixture of pulmonary and cardiac formsforms

Signs of one may be predominateSigns of one may be predominate The mixed form is more The mixed form is more

frequently seen at necropsyfrequently seen at necropsy

http://www.vet.uga.edu/vpp/IVM/ENG/Horse/index.htm

Clinical Signs: Mixed Form Clinical Signs: Mixed Form (acute)(acute)

Clinical Signs: Clinical Signs: Mixed Form (fever)Mixed Form (fever)

Mildest formMildest form Can be subclinical or inapparentCan be subclinical or inapparent Occurs in zebras, donkeys, and horses with Occurs in zebras, donkeys, and horses with

heterologous immunity.heterologous immunity. Fever is usually intermittent—usually normal Fever is usually intermittent—usually normal

temperature in the morning, but is febrile in temperature in the morning, but is febrile in the afternoonthe afternoon

Fever may reach 104Fever may reach 104°F in 1 or 2 days°F in 1 or 2 days

Clinical Signs: Clinical Signs: Mixed Form (fever)Mixed Form (fever)

Other Clinical Signs:Increased respiratory rateMild conjunctival congestion Accelerated pulseLoss of appetite is rare and mild

After 1 or 2 days, there is a rapid recovery

Morbidity is dependant upon exposure

Mortality varies with serotype and strain; mortality in naïve horses can be high

Post Mortem LesionsPost Mortem Lesions

Sudden Death

Pulmonary edema

Pulmonary edema not seen in all cases;

Rarely seen in euthanized animals

Pulmonary EdemaPulmonary Edema

Pulmonary edema

Hydropericardium

Myocardial necrosis

Edema elsewhere

Hemorrhages

LesionsLesions

http://www.iah.bbsrc.ac.uk/images/Culicoides.jpg

AHSv is spread primarily by AHSv is spread primarily by CulicoidesCulicoides (ex: (ex: biting flies and mosquitoes) by transfer of biting flies and mosquitoes) by transfer of bloodblood– CulicoidesCulicoides are biological vectors because the are biological vectors because the

disease can replicate in the midgedisease can replicate in the midge– In U.S., In U.S., CulicoidesCulicoides that can transmit that can transmit

bluetongue virus most likely can transmit bluetongue virus most likely can transmit African Horse SicknessAfrican Horse Sickness

– Culicoides Culicoides are most active at sunset and about are most active at sunset and about sunrisesunrise

African Horse Sickness is African Horse Sickness is non-contagiousnon-contagious, , but the horse is an amplifier of AHS virus but the horse is an amplifier of AHS virus and source of virus for arthropods. and source of virus for arthropods.

Arthropods other than Arthropods other than CulicoidesCulicoides may may spread the virus as mechanical vectors spread the virus as mechanical vectors

Other VectorsOther Vectors

Aedes aegyptiAedes aegypti Anopheles sephensiAnopheles sephensi Culex PipiensCulex Pipiens Hyalomma dromedariiHyalomma dromedarii Ripicephalus sanguineusRipicephalus sanguineus

This particular virus favors warmer This particular virus favors warmer conditions, when it has a preferred vector conditions, when it has a preferred vector available. It may move best in moist, mild available. It may move best in moist, mild conditions and travel long distances on the conditions and travel long distances on the wind-borne vectors.wind-borne vectors.

Virus CharacteristicsVirus Characteristics

The virus can be inactivated by:

repeated freezing and thawing

by treatment with acetic acid, at pH of 6.3 or lower, remaining for 2 weeks at 37°C, or being placed for 5 minutes at 70°C.

DiagnosisDiagnosis

AHS is difficult to pinpoint in early febrile AHS is difficult to pinpoint in early febrile stagesstages

Suspect the disease during the season Suspect the disease during the season when there are insect vectorswhen there are insect vectors

DiagnosisDiagnosis

Suspect when horses develop the Suspect when horses develop the following:following:– FeverFever– DyspneaDyspnea– Edema of the supraorbital fossa Edema of the supraorbital fossa – Subcutaneous edema of head/neck areasSubcutaneous edema of head/neck areas– Pulmonary edemaPulmonary edema– DeathDeath

Laboratory diagnosisLaboratory diagnosis

Virus isolation – blood from live Virus isolation – blood from live animal; spleen from dead animalanimal; spleen from dead animal

Vero cells, embryonating eggs, suckling Vero cells, embryonating eggs, suckling mouse brainmouse brain

Serology – CF test, ELISASerology – CF test, ELISA

Virus is closely associated with erythrocytes

Differential DiagnosisDifferential Diagnosis

Anthrax Anthrax BotulismBotulismEquine infectious anemia Equine infectious anemia Equine viral arteritis Equine viral arteritis High doses of pyrrolizidine alkaloidsHigh doses of pyrrolizidine alkaloidsTrypanosomosis Trypanosomosis Equine encephalosis Equine encephalosis Piroplasmosis Piroplasmosis Purpura haemorrhagica Purpura haemorrhagica

ControlControl

Movement restrictionMovement restriction

Vector controlVector control

Test and slaughterTest and slaughter

VaccinationVaccination– MLVMLV– Inactivated virusInactivated virus

Vaccine in South AfricaVaccine in South Africa

DiseaseDisease – Economic – Economic ImpactImpact

Horse study reveals Horse study reveals almost $40 billion almost $40 billion impact on U.S. impact on U.S. economyeconomy

Staff Reports, Staff Reports, Oroville Mercury-Register Oroville Mercury-Register July 23, 2005July 23, 2005

Donkeys and Mules are a growing segment of the equine industry

DiseaseDisease – Economic Impact – Economic Impact

The horse industry in the United The horse industry in the United States contributes $39 billion in States contributes $39 billion in direct economic impact to the U.S. direct economic impact to the U.S. economy and supports 1.4 million economy and supports 1.4 million jobs on a full-time basis, according jobs on a full-time basis, according to a new study released today by the to a new study released today by the American Horse Council (AHC). American Horse Council (AHC).

When indirect and induced spending When indirect and induced spending are included, the industry's are included, the industry's economic impact reaches $102 economic impact reaches $102 billion. billion.

The study also estimates the horse The study also estimates the horse population in this country has population in this country has reached 9.2 million.reached 9.2 million.

World Distribution of DiseaseWorld Distribution of Disease

http://www.vet.uga.edu/vpp/IVM/ENG/Horse/vector.htm

African Horse Sickness- African Horse Sickness- ReferencesReferences

1) "African Horse Sickness." 1) "African Horse Sickness." OIE OIE . 22 Apr. 2002. 12 July 2005 . 22 Apr. 2002. 12 July 2005

<http://www.oie.int/eng/maladies/fiches/a_A110.htm>. <http://www.oie.int/eng/maladies/fiches/a_A110.htm>.

2) Barnard, B. J. H. (1998). 2) Barnard, B. J. H. (1998). Epidemiology of African Horse Epidemiology of African Horse

Sickness and the Role of the Zebra in South Africa. Sickness and the Role of the Zebra in South Africa. African African

Horse SicknessHorse Sickness. P. S. Mellor, et al. Vienna, Austria, Springer-. P. S. Mellor, et al. Vienna, Austria, Springer-

Verlag: 13-19.Verlag: 13-19.

3) Corrie Brown “Pathology of Foreign Animal Diseases: African 3) Corrie Brown “Pathology of Foreign Animal Diseases: African

Horse Sickness”Horse Sickness”

ReferencesReferences

4) 4) Foreign Animal DiseasesForeign Animal Diseases (1992). United States Animal Health (1992). United States Animal Health

Association. Cummings Corporation and Carter Printing Company, Association. Cummings Corporation and Carter Printing Company,

Richmond, VA.Richmond, VA.

5) Geering, W. A., Forman, A. J., and Nunn, M. J. (1995) 5) Geering, W. A., Forman, A. J., and Nunn, M. J. (1995) Exotic Exotic

Diseases of Animals: a field guide for Australian veterinarians.Diseases of Animals: a field guide for Australian veterinarians.

Australian Government Publishing Service, Canberra.Australian Government Publishing Service, Canberra.

6) 6) Keeping America Free From Foreign Animal DiseasesKeeping America Free From Foreign Animal Diseases. Vol. 1. . Vol. 1.

African Horse Sickness. USDA, 1997. African Horse Sickness. USDA, 1997.

7) 7) Good Emergency Management Practice. Good Emergency Management Practice. Plum Island 2002 CD-3Plum Island 2002 CD-3

ReferencesReferences

8.8. Professor Alan Guthrie, U of Pretoria Dept of Tropical Vet Med, Professor Alan Guthrie, U of Pretoria Dept of Tropical Vet Med, “African Horse Sickness” FEAD course Tenn, Aug 1-5, 2005. (ppt “African Horse Sickness” FEAD course Tenn, Aug 1-5, 2005. (ppt and video)and video)

9.9. Corrie Brown, DVM PhD University of Georgia, Dept of Pathology Corrie Brown, DVM PhD University of Georgia, Dept of Pathology “African Horse Sickness” PowerPoint presentation“African Horse Sickness” PowerPoint presentation

Image WatermarksImage Watermarks

Pathological lesion images marked “USDA” were Pathological lesion images marked “USDA” were taken by staff photographers at the Plum Island taken by staff photographers at the Plum Island Animal Disease Center lab and were presented Animal Disease Center lab and were presented by Dr Corrie Brownby Dr Corrie Brown

Images marked “Logan” were provided by Dr Images marked “Logan” were provided by Dr Linda Logan, USDA APHIS IS, CairoLinda Logan, USDA APHIS IS, Cairo

Images of symptoms marked “Guthrie” were Images of symptoms marked “Guthrie” were presented in Tennessee by Dr Alan Guthriepresented in Tennessee by Dr Alan Guthrie

AcknowledgementsAcknowledgements

Special thanks to:Special thanks to:

Corrie Brown, DVM PhDCorrie Brown, DVM PhD

Robin Sewell, DVM, Librarian Robin Sewell, DVM, Librarian

Kelsey Pohler- Research Assistant Kelsey Pohler- Research Assistant

Tita Burnham – Student AssistantTita Burnham – Student Assistant

African Horse Sickness Texas A&M University Texas A&M University College of Veterinary...

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