Epidemiology of Plague in the US

Skin Zoonotic Diseases

Epidemiology of Plague in the US

Skin Zoonotic Diseases

VM 544 Veterinary Preventive Medicine

Dr. Paul Bartlett, MPH., DVM., Ph.D.

Yersinia pestis (Pasteurella pestis)Yersinia pestis (Pasteurella pestis)Remarkable history, called the “Black

Death” and “Peste.”First Pandemic - 542 AD to 602 AD - during the rule of Byzantine Emperor Justinian - the black death killed about 100 million people - destroying the Byzantine Empire.

Second Pandemic - 14th to 16th Centuries - in central Asia to Europe - it killed hundreds of millions and eventually reached all of Africa and Asia.

Mode of TransmissionMode of Transmission There are domestic and sylvatic cycles of disease. Domestic:

This reservoir is maintained by transmission among domestic rodents through fleas and direct contact.This does not occur in the USA at this time, but the domestic cycle could become established at any time.This cycle/reservoir is important in many developing countries.

Sylvatic:This cycle involves transmission of the agent among numerous species of wildlife rodents by fleas, cutaneous direct contact, aerosol, and ingestion.

Transmission to HumansTransmission to Humans direct contact with infected

animals.hunters can be exposed through sores or cuts on their hands when they clean game.

direct respiratory spread from wild rodents is possible.

ingestion. through fleas of wild rodents

which harbor the bacterium.most common mode in U.S.

Clinical SyndromeClinical Syndrome

The classic form of the disease is called “Bubonic Plague”

The incubation period is 2 to 6 days.A primary lesion occurs at the site of exposure (most usually from a flea) but could also occur through direct contact with a wound or maybe intact skin.The infection then spreads to regional lymph nodes draining the area of the primary lesion.

Clinical SyndromeClinical Syndrome The bubonic plague can spread to the lungs. Once it spreads to the lungs, the resulting syndrome

is called the “secondary pneumonic plague”About 22% of bubonic cases develop secondary pneumonic plague.

Once this occurs, respiratory transmission is possible to other animals (or people) - who then develop “primary pneumonic plague”.

The overall case fatality rate for pneumonic plague is 18% in the USA.

Primary lesion of bubonic plague

Primary lesion of bubonic plague

Primary lesion of bubonic plague

Primary lesion of bubonic plague

Swollen lymph nodes called “buboes”.

A veterinarian in the Southwest with bubonic plague.

Bubonic Plague - Primary lesion and buboes

Swollen lymph nodes called “buboes”.

Swollen lymph nodes called “buboes”.

Pneumonic plague – involved mediastinal lymph nodes

Incidence and Disease SurveillanceIncidence and Disease Surveillance

Children are more likely to be infected, but older people have a higher case fatality rate.

Males are at higher risk.The disease is cyclic and is now in

a down-swing.

Usage of dogs as sentinels of infection:Dogs become seropositive, but rarely develop clinical signs.Serosurveys of dogs are helpful in identifying areas of high plague prevalence in wildlife rodents.

Lots of DVMs work on plague surveillance.

Thirsty?

Looking for fleas.

Prairie dog die-off

Prairie dog die-off

Prairie dog die-off

Pets and the Black DeathPets and the Black DeathOur unassuming dogs and cats can serve as a

bridge for infection between rodents and humans.

Dogs and cats bring infective fleas into the home environment.By direct-contact contamination from a severely ill cat.

– Cats get sick. Can infect people by direct contact or they can get bubonic plague that becomes pneumonic. Can spread via respiratory route to people.

– Dogs usually don’t get sick or transmit.

Prevention and ControlPrevention and Control1. Eliminate rodent habitats.2. Do not feed or encourage rodents to live nearby (squirrels are

rodents too.)3. Leash dogs and cats in endemic areas.4. Flea control for dogs and cats (very important fro veterinarians.)5. Insect repellent for people, pets.6. Reporting of rodent die-offs.7. Client education not to handle sick or dead rodents.8. Vaccine available fro high risk people., but it is only effective for

less than 6 months.9. Early antibiotic therapy is the key to clinical treatment.

Plague case report # 1Plague case report # 1

Evergreen Colorado Veterinarian – 49 yrs oldApril 15 - Vertigo, fever, chills, malaise,

L. node swelling in rt. Axilla.April 16 – Saw physician (Tylenol)April 18 4 x 500 mg tetracycline (self)April 19 Hospitalized (recovered)

Plague Case Report # 1 (continoud) Plague Case Report # 1 (continoud)

Epi investigationApril 10 - Dead rodent contact while jogging

April 13 – Bite from cat–Bled cat May 5 (>8192 titer for plague)–Cat’s neighborhood

3/13 dots had low plague titersEvidence of recent rodent die-off

Plague Case Report # 2Plague Case Report # 2California 47-years old female. Fatality. Primary plague pneumonia from house cat that

also caught birds and rodents.Sept 26 – cat illSept 28 – Cat acutely ill, coughing,

hemoptysis, vet consulted on phone, no action or exam.

Sept 29 – cat dies

Plague Case Report # 2 (continued)Plague Case Report # 2 (continued)

Oct 2 – Lady ill with cough, fever, malaise.

Oct 3 – Saw physician Dx = urinary tract infection.

Oct 4 Hospitalized, died in 5 hours.Aftermath – 180 contacts treated with

antibiotics for exposure to the ill lady.

Plague Case Report # 2 (continued)Plague Case Report # 2 (continued)

Cat exhumed – cervicle buboes and plague pneumonia.

NeighborhoodRecent rodent die-off

1/9 dogs positive for plague

Dead rodent found across street – culture positive for plague.