Emerging Infectious Diseases

Lecture 8 outline & Sample Questions

J.M.Bowen

Emerging Equine Diseases

Encephalitides

§ Venezuelan Equine Encephalitis

§ West Nile Encephalitis

§ Nipah virus disease

§ Borna disease

§ Japanese Equine Encephalitis

§ Semliki Forest Equine Encephalitis

§ Near East Encephalitis

Venezuelan Equine Encephalitis

§ This disease is endemic in South and Central America.

§ Fatal to both horses and man.

§ Major epidemic in 1969 spread to north through Mexico to Texas in 1971.

§ Morbidity and mortality greater than with either eastern or Western Encephalitides.

§ Man can be infected by handling affected tissues.

Eastern Equine Encephalitis

§ Common on the East & Gulf Coasts of U.S.

• Mosquito-borne disease.

§ Seasonal incidence

• May infect pigs and humans.

• Disease is not spread from horses to humans.

§ Disease at first resembles laminitis or colic.

§ Morbidity - low

§ Mortality - high

§ More virulent strain in Virginia this Summer.

West Nile Encephalitis

§ Endemic in Africa, Middle East, India.

§ Occurs sporadically in Southern Europe

§ Recent arrival in the United States (NY, NJ)

• 13/22 horses died on Long Island in 1999.

• June 2000 - 2 dead birds (+) found in NY state.

• June 2000 - May have been found in Delaware?

§ Mosquito-borne, but has been found in ticks.

• Birds are a sentinel for West Nile Fever.

§ Vaccination against Western and Eastern encephalitides will NOT confer any protection against West Nile Fever.

West Nile Virus - 2000

Hendra Virus Disease

§ First seen in 1994

• 13 horses died, as well as their trainer.

§ Second incident in Mackay

• 2 horses and a farmer died

§ Virus has been found in black fruit bats.

§ Also been found in flying foxes (bat spp.)

§ Fatal encephalitis in both man and horses.

Nipah Virus Disease

§ Caused by a paramyxovirus

• Distemper, measles, rhinderpest

§ Also associated with Hendra virus

§ Natural host is the flying fox (bat).

§ Primarily a disease of pigs.

§ Will affect humans and horses.

§ Has killed horses in Australia.

• Low morbidity, high mortality in horses.

• Seroconversion in horses.

Spread of Nipah Virus Infections

Worldwide Distribution of Equine Encephalitides

Other Encephalitides

§ Japanese Equine Encephalitis

• Flavivirus, similar to Murray Valley & West Nile encephalitides viruses

§ Man & horses affected

§ Semliki Forest Equine Encephalitis

• Related to Venezuelan Encephalitis

§ Horse is an aberrant host.

§ Near East Encephalitis

• Tick borne virus related to Borna fever?

§ Suppurative meningoencephalitis

Worldwide Distribution

Equine Borna Disease

§ Common viral disease in Central Europe.

• Incubation period of around 28 days.

• Recent report of two cases in Austria

• Signs:

§ Pyrexia (40 - 41°C); apathy; oliguria; jaundice; leading to teeth grinding; ataxia; circling; difficulties in swallowing.

§ The neurological signs worsened over the next 5 - 6 days

• Post-mortem examination

§ Disseminated nonsuppurative meningoencephalitis

Other Viral Diseases

§ African Horse Sickness

• South Africa

§ Vesicular Stomatitis

• United States and Central & South America

§ Hendra virus disease

• Australia

§ Equine Infectious Anemia

• United States

§ Equine Viral Arteritis

African Horse Sickness

§ Sub-Saharan Africa, occasionally N.Africa.

§ Reservoir still unknown

• Elephants? Dogs? Onager? Camels?

§ Transmission by Culicoides spp. and ticks?

• Mortality in horses 70 - 95%

• Mortality in mules 50%: donkeys 10%

§ Disease has spread to Spain and Portugal

African Horse Sickness

§ Cardiac form

• Swelling of the head, eyelids & neck

§ Death within 48 hours to 1 week

§ Respiratory form

• Acute form

§ Dyspnoea, cough, frothy fluid coming from nostrils.

§ Death due to anoxia

• Autopsy

§ Lungs full of frothy blood tinged fluid.

Vesicular Stomatitis

§ Occurs in the Americas

• Sporadic (once every ten years) in Mid-West.

§ Affects horses, cattle, swine, deer & humans.

§ Colorado, New Mexico, Missouri, Kansas.

§ High morbidity: low mortality

§ Resembles foot & mouth disease.

§ Arthropod transmission

Equine Infectious Anemia

§ Swamp Fever

• Caused by a retrovirus

§ Slow progressive wasting disease, often fatal.

§ No vaccine available

§ Coggins Test

• Branding and isolation; euthanasia

• Inapparent carriers are a danger to healthy horses.

EIA Cases – 2000

Areas where EIA is increasing 1991-2000

Equine Viral Arteritis

§ Not a new disease in the United States

§ Showing signs of a resurgence

§ Originally confined to Standardbred horses.

• Seen also in imported Warmbloods.

§ Originally thought to be a respiratory disease.

§ Now known to be spread venereally.

• Infected stallions shed virus in semen for years.

Protozoal Diseases

§ Piroplasmosis

• Equine Babesiosis

§ Trypanosomiasis

• Surra

• Dourine

§ Equine Protozoal Myeloencephalitis

Equine Babesiosis

§ Tick borne disease

• Caused by either Babesia caballi or Babesia equi.

§ Transmitted by Dermacentor, Hyalomma or Rhipicephalus species of tick.

§ B equi is the more pathogenic of the two.

§ Young animals are the least susceptible to the disease.

§ Immunity last only a year or two.

Trypanosomiasis

§ Surra

• Trypanosoma evansi

§ Africa.

• Trypanosoma equinum

§ S. America.

§ Dourine

• Trypanosoma equiperdum

§ Middle East; Russia(?); South America; North Africa

§ Venereal disease of horses

• Transmitted by coitus

Equine Protozoal Myeloencephalitis

§ Equine protozoal myeloencephalitis.

• Caused by Sarcocystis neurona.

• A small parasitic protozoan.

§ Horse is an aberrant host.

• Parasite may settle in the spinal cord.

§ Causes incoordination and paralysis.

§ Opossum is one of the host species.

§ Birds may be the other?

§ Vaccine recently approved

Bacterial Diseases

§ Strangles

§ Salmonella

• Antibiotic resistant strains

§ Glanders

§ Melioidosis

§ Leptospirosis

§ Ulcerative Lymphangitis

Strangles

§ Bacterial disease which was almost eradicated after the discovery of penicillin.

§ Resurgence due to the use of ‘more effective’ antibiotics in equine practice.

§ Affects the very young and the very old.

• Caused by Streptococcus equi equi.

§ Pseudostrangles

• Similar signs due to Strep. equi zooepidemicus.

Salmonella

§ More than 2000 serotypes of Salmonella.

§ Commonest in reptiles.

§ New variants causing disease in cattle.

§ Horses are often inapparent carriers.

• 32% sampled had Salmonella without signs.

§ Stress will cause an inapparent carrier to ‘break’ with Salmonellosis.

Glanders

§ Contagious disease of horses, dogs and man.

§ Sporadic in the Middle East, India & Far East.

§ Horse is most commonly affected.

§ Signs

• Pulmonary (acute) form, seen in donkeys and mules

• Nasal form, thin discharge becoming purulent and bloody.

• Cutaneous (farcy) form, Farcy buds form on the hind limbs which burst and exude a grey oily pus

§ Treatment

• Euthanasia

Melioidosis

§ Glanders-like disease

• Disease of rodents, but sheep, goats & horses can become affected.

• Reported in S.E. Asia, Australia, Malaysia.

§ Signs:

• Fever, coughing, nasal and ocular discharges.

§ Autopsy

• Multiple abscesses in lung, liver and spleen.

§ Treatment

• Euthanasia

Leptospirosis

§ Mostly a disease of rodents.

§ Associated with contaminated water

§ Transmitted via the urine.

§ Causes Periodic Ophthalmia in horses.

• Leptospira vaccines can also cause periodic ophthalmia in horses. Do NOT use!

§ Associated with poor hygienic conditions.

Ulcerative Lymphangitis

§ Contagious disease of horses.

• Corynebacterium pseudotuberculosis

§ Occurs mainly in Africa, may occur in Greece, Iraq, Burma, Mexico & Jamaica

§ Signs:

• Hind leg hot, painful and swells,

• Nodules for, which burst and ulcerate.

§ Treatment

• Oxytetracycline for 5 days.

PARASITIC DISEASES

§ Screwworm myiasis

• Recently imported into the United States.

§ Horse in quarantine from the Argentine.

§ Cyanthostomes

• Small strongyles

§ Encysted forms are an increasingly a problem.

§ Simultaneous migration of hypobiotic forms

§ Tapeworm infestation

• Increasingly a cause of colic in horses.

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Sample Questions

1. Which of the following statements is correct?

a.) West Nile Virus has been established in the United States for all of this century.

b.) West Nile Virus is only a sporadic visitor to the United States.

c.) West Nile Virus is transmitted by opossums.

2. Which of the following statements is correct?

a.) Venezuelan Equine Encephalitis is commonly found in Texas.

b.) Venezuelan Equine Encephalitis is fatal to both horses and humans.

c.) Humans cannot become infected by handling tissues infected by Venezuelan Equine Encephalitis

3. Which of the following statements is incorrect?

a.) Transmission of African Horse Sickness is by biting flies.

b.) African Horse Sickness has occurred in places outside Africa.

c.) African Horse Sickness is equally fatal to both horses and donkeys.

4. Which of the following statements is correct?

a.) There is no vaccine available for Equine Infectious Anemia.

b.) There is no test for this disease.

c.) All animal suspected of having this disease have to be slaughtered.