Zoonotic Pathogens: An Introduction

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Zoonotic Pathogens An Introduction

• Dr. Emilo DeBess
• Oregon Health Division
• Dr. McKinley Thomas
• Augusta State University

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Zoonotic Diseases

• ...cause infections in animals and can be
  transmitted to humans
• are typically endemic and occur in a natural
  foci
• However, ecologic changes and meteriologic or
  climate events can promote epidemic expansion of
  the host and geographic range.

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History

• Interactions between animals and humans have
  occurred since the beginning of time.
• As animals became domesticated and a close bonds
  developed between animals and humans, the
  occurrence of zoonotic diseases increased.

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Significant Zoonitic Pandemics

• 1700s, Mongols invaded Europe
• Mongols carried plague with them
• This lead to black death or plague pandemic
• Killed 1/3 of European population

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Significant Zoonitic Pandemics

• Early 1900s
• Spanish flu transmitted from pigs to humans
• Decimated 20 million people worldwide
• Continues to pose a threat to humans

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Contemporary Threats

• Potential Human Pathogens
• E. coli 0157H7
• Caliciviruses (evolved from the sea)
• Bovine Spongiform Encephalopathy (BSE) also known
  as mad cow disease

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Etiology

• Todays threat involving zoonotic diseases is
  considered to be partly due to human involvement
  in which the artificial multiplication of these
  pathogens can be used as biological terrorism.

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Prevalence

• Largely Unknown
• Both serological studies and anecdotal discussion
  have been used to generate estimates
• 1997 a study trying to asses the prevalence of
  antibodies against Bartonella henselae and B.
  quintana was done at a veterinary conference. The
  results indicated that 7.1 of the veterinary
  population had antibodies which was no different
  from the general population studies at an earlier
  time.

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Believed More Common

• Ringworm caused by Trychophitum species. believed
  to be heavily under diagnosed / not reported
• More prevalent among children

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Common Zoonotic Diseases

• Bacterial
• Plague
• Cat Scratch Fever
• Salmonellosis
• Parasitic
• Toxoplasmosis
• Ring Worm
• Viral
• Hantavirus
• Prion
• BSE

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Plague
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Plague in History

• Pandemics in history involving Europe, Asia,
  Africa
• The Black Death, thought to be caused by
  displeasure of the gods or other supernatural
  powers, heavenly disturbances
• The etiologic agent, Yersinia pestis, first
  isolated in 1894 (Yersin and Kitasato)

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Cat Scratch Disease

• One estimate by the Centers for Disease Control
  found that there were 2.5 cases of CSD per
  100,000 people per year in the United States.
• In recent years, many studies have implicated
  the gram negative bacterium Bartonella henselae
  as the primary (but not the sole) cause of CSD
• Typically, a small skin lesion (resembling an
  insect bite) develops at the site of a cat
  scratch or (less commonly) a bite, followed
  within two weeks by swollen lymph nodes and
  sometimes a fever.

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Cat Scratch Disease

• Cats are the main reservoir for B. henselae.
  Surveys for B. henselae antibodies in cats in the
  United States have found average infection rates
  to be from 25 to 41 in clinically healthy cats.
  
• The lowest rates were in the Midwest and great
  plains regions (4-7) and the highest were in the
  southeast (60). Warmer, more humid climates are
  most supportive of fleas, which have been shown
  to transmit B. henselae from cat to cat.
• It appears that the majority of cats do not
  become ill when they are infected with this
  bacterium and kittens are more commonly infected
  than adults.

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Cat Scratch Disease

• CSD is primarily a concern in homes with
  immunosuppressed people.
• Since kittens are more likely to carry B.
  henselae than adult cats, it is recommended that
  people with compromised immune systems adopt cats
  older than 1 year of age to reduce the risk of
  contracting CSD.

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Cat Scratch Disease

• Since carrier cats are always healthy and
  multiple
• cases of CSD within a household are rare,
  euthanasia of a suspected carrier is not
  warranted.
• Onychectomy (declawing) is also not recommended,
  since infection can occur without a cat scratch.
• As is always the case, any cut or scratch should
  be promptly washed with soap and water.

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Reptile-Associated Salmonellosis
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Reptile-associated Human Salmonella
History
1944 First Salmonella sp. isolate from
snakes. 1946 First Salmonella sp. isolate from
turtles and lizards. 1963 Turtle-associated
salmonellosis first described. 1972 FDA
regulation requiring certification of turtles for
sale as "Salmonella-free." 1974 Study shows
300,000 turtle-associated human salmonellosis
cases per year in U.S. 1975 FDA bans sale of
viable turtle eggs or live turtles with
carapace length lt 10.2 cm. 1977 CA State
regulations ban sale, as above.
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Reptile-Associated Salmonellosis

• In the United States, pet turtles were an
  important source of salmonellosis until
  commercial distribution of pet turtles less than
  4 inches long was banned in 1975.
• This ban led to a 77 reduction in the frequency
  of turtle-associated Salmonella serotypes
  isolated from humans during 1970-1976.

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Reptile-Associated Salmonellosis

• Approximately 93,000 (7) cases per year of
  Salmonella infections are attributable to pet
  reptile or amphibian contact.
• An estimated 3 of households in the United
  States have a reptile (CDC, unpublished data,
  1999)

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Reptile-Associated Salmonellosis

• Kansas. During April 1997, a 6-year-old boy had
  bloody diarrhea of 10 days' duration, abdominal
  cramps,vomiting, and fever (104.9 F 41 C).
  Stool culture yielded Salmonella serotype
  Typhimurium. The child was treated with
  ceftriaxone and amoxicillin / clavulanate.
• Nine days after the boy started therapy, his
  3-year-old brother also developed diarrhea, and a
  stool sample yielded S. Typhimurium..

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Reptile-Associated Salmonellosis

• No other family members became ill. The two boys
  shared a room with two corn snakes that they
  handled regularly. Stool cultures from the corn
  snakes yielded S. Typhimurium.
• The parents reported to health department staff
  that they were unaware that snakes are a source
  of salmonellosis

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Salmonella Infection in Reptiles

• Numerous serotypes reported (5 or more may be
  isolated from a single reptile specimen).
• Latent infections with reactivation resulting in
  intermittent shedding
• Usually asymptomatic (wound infections, septic
  arthritis, endocarditis reported after
  inoculation via bites/scratches).

DIFFICULT TO IDENTIFY OR ELIMINATE CARRIERS.
Chiodini RJ, Am J Epidemiol 1981.
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MMWR November 12, 1999
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Recommendations to Prevent Human
Reptile-associated Salmonellosis

• Do not keep reptiles as pets where high risk
  individuals may be exposed such as infants, the
  elderly, and people with compromised immune
  systems.
• Thoroughly wash hands after any contact with
  reptiles, including handling of the animal or its
  cage.
• Confine reptiles to prevent environmental
  contamination. For example, keep reptiles off of
  floors and rugs where infants crawl and out of
  tubs and sinks where infants are bathed.

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Toxoplasmosis

• Toxoplasmosis is a disease caused by microscopic
  parasite called Toxoplasma gondii.
• It is not a new disease, having first been
  discovered in 1908. Since its discovery,
  toxoplasmosis has been found in virtually all
  warm-blooded animals including most pets,
  livestock, and human beings.
• Nearly one-third of all adults in the U.S. and in
  Europe have antibodies to Toxoplasma, which means
  they have been exposed to this parasite.

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Toxoplasmosis

• There are 3 principal ways Toxoplasmosis is
  transmitted
• 1.Directly from pregnant mother to unborn child
  when the mother becomes infected with
  Toxoplasmosis during pregnancy.
• 2.Consumption and handling of undercooked or raw
  meat from infected animals.
• 3.Ingestion of food or water or inhalation of
  dust contaminated with a very resistant form of
  Toxoplasmosis called the oocyst.

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Toxoplasmosis

• Toxoplasma in meat can be killed by cooking at
  152ºF (66ºC) or higher or freezing for a day in a
  household freezer.
• Of all the infected animals tested, only cats
  are the perfect hosts for the production of the
  infectious and resistant Toxoplasma oocysts.

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Toxoplasmosis

• There are two populations at high risk for
  infection with Toxoplasma pregnant women and
  immunosuppressed individuals. In the United
  States it is estimated that approximately 3,000
  children are born infected with toxoplasmosis
  every year.
• Although the majority of infected infants show no
  symptoms of toxoplasmosis at birth, many are
  likely to develop signs of infection later in
  life.
• Loss of vision, mental retardation, loss of
  hearing, and death in severe cases, are the
  symptoms of toxoplasmosis in congenitally
  infected children.

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Toxoplasmosis
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Hantavirus
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Hantavirus Pulmonary Syndrome Cases by State of
Residence
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14
7
1
2
2
5
6
1
14
2
3
1
5
1
12
1
2
1
24
14
1
14
33
1
1
31
41
1 - 5 cases
6 - 10 cases
1
11 -15 cases
13
1
gt15 cases
277 cases in 31 states
10/4/2000
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Transmission of Hantaviruses
Chronically infected rodent
Horizontal transmission of infection by
intraspecific aggressive behavior
Virus also present in throat swab and feces
Virus is present in aerosolized excreta,
particularly urine
Secondary aerosols, mucous membrane contact, and
skin breaches are also a consideration
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Hantavirus
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BSE

• Since 1996, evidence has been increasing for a
  causal relationship between ongoing outbreaks in
  Europe of a disease in cattle, called Bovine
  Spongiform Encephalopathy (BSE, or "mad cow
  disease"), and a disease in humans, called new
  variant Creutzfeldt-Jakob disease (nvCJD).
• Both disorders are invariably fatal brain
  diseases with unusually long incubation periods
  measured in years, and are caused by an
  unconventional transmissible agent.

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Ringworm

• Ringworm is a fungus infection of the scalp or
  skin. Symptoms include a rash that is often itchy
  and flaky
• Ringworm is spread by direct contact with a
  person or animal infected with the fungus.
• The same fungi that infect humans can also infect
  animals such as dogs, and cats, and infections
  may be acquired from pets as well as from
  infected children.

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Bibliography

• Swedish Institute of Infectious Disease Control.
  (2001). Available http//www.smittskyddsinstitu
  tet.se/
• Control of Communicable Diseases Manual James
  Chin, MD 17th edition
• Centers for Disease Control and Prevention
  www.cdc.gov
• We would like to acknowledge Michelle Jay, DVM,
  MPVM for providing materials for this
  presentation.