Learning Center
Plans & pricing Sign in
Sign Out

Animal Transmitted Microbial Diseases


									Animal-Transmitted Microbial
       Zoonotic Diseases
• Deforestation (road building, mining,
  agriculture, etc.)
• Dam building

• Alter our contact with the animals that
  carry and transmit many of the above
     Geographic Distribution
• Determined by animal vector and/or
  animal reservoir.
• Sensitive to climate changes.
         Animal Reservoirs
• Many infectious diseases can survive in
  other animals, causing few or no
  symptoms there
• This enables the infectious agent to
  survive after a human epidemic is
           Animal Reservoirs
•   Influenza: pigs, birds
•   Rabies: bats, foxes, dogs, skunks
•   Western equine encephalitis: horses, birds
•   Lyme disease: mice
•   Malaria: monkeys
•   Ebola: apes, bats?
•   SARS: Bats?
•   HIV: sooty mangabay (monkey)?
• A fatal encephalitis.
• Virus is shed in saliva of infected animals.
• Can enter small scratches and cross
  mucous membranes.
     Progression of Infection
• Following bite, virus multiplies in
  surrounding skeletal muscle – days to
• Enters peripheral nerves.
• Travels along them to CNS – 15-100 mm
  per day.
• Immune response is not possible until
  destruction of CNS nerves begins.
        Symptoms of Rabies
• Following CNS infection: alternating
  agitation and calm, muscle spasms in
  mouth and pharynx, rage, biting, paralysis,
  death within a few days.
• Virus can be detected in saliva, blood,
  CSF (and brain after death).
Rabies virus in human brain
• Postexposure prophylaxis – possible
  because of slow progression of early
• Vaccine is grown in chicken embryos..
• Rabies immune globulin is also given
• Given following a bite from an infected
  animal or one whose status is unknown
  (esp. skunks, bats, foxes, raccoons).
             Lyme Diseae
• Borrelia burgdorferi – gram-negative
• Transmitted by Ixodes ticks
• Field mice (and deer) are reservoirs
• Disease first noticed in 1975
• Bacterium isolated in 1983
Ixodes scapularis
           Ixodes pacificus
• Western black-legged tick
• Also feeds on lizards
• Thus, few ticks are infected
• 1st symptom:
  expanding bull’s eye
  rash; up to 15 cm
• Fever, aches as rash
• Antibiotics are
  effective at this stage
• Later stages usually affect nervous system
  – facial paralysis, meningitis, encephalitis
• Arthritis – immune response in joints
Passenger Pigeon & Lyme Disease
• Extinction of other animals: it is thought
  that the extinction of the N. American
  passenger pigeon in the eastern U.S. has
  led to the rise in Lyme disease
  – Last bird died in 1914. It had been the most
    abundant land bird in North America! Its
    extinction opened up a niche for deer and
• Chills, fever, vomiting, headache last 2-3
  days; alternates with asymptomatic period.
• Anopheles mosquitoes (night feeders)
  carry Plasmodium protozoan.
• Tropical areas report 300-500 million
  cases, 1-2 million deaths per year.
• Many people contract malaria several
  times in their lifetime.
• Range of disease has expanded.
      Plasmodium falciparum
• Most dangerous species.
• Destroys RBCs – anemia.
• Some RBCs stick to capillary walls,
  clogging them.
• Within 30 minutes of bite, parasite infects
• Liver releases many merozoite forms
  (RBC destroyers).
             Other Species
• P. vivax – prevalent in Asia.
  – Can survive in liver for months.
• P. ovale
Plasmodium vivax
• Many stages to its life cycle.
• Merozoite stage infects RBCs.
• Different stages enable it to evade
  immune system and anti-malarial drugs.
• Antigenic variation in sporozoite.
• People with sickle-cell anemia (or carriers)
  have some resistance.
•   Quinine
•   Chloroquine, primaquine, mefloquine
•   Resistance is evident
•   Malarone is newer
•   Derivatives of artemisinin.
    – ACT = Artemesinin-based Combination
Plasmodium lifecycle
       Malaria Vaccine Trials
1. Proteins from Plasmodium sporozoite.
  •   Add adjuvant.

2. Live, Attenuated parasites.
  •   Cultured in mosquitoes.

1. Transmission-blocking Vaccines.
  •   Proteins from gametocyte or from mosquito.
• Arthropod-borne
• Can replicate in arthropod and vertebrate
• Often amplified in arthropod gut, then
  infect salivary glands (7 – 14 day cycle)
• Some can be transmitted from mother to
• ~100 million cases per year.
• Fever, muscle & joint pain, rash.
• Recovery is typical.
• Carried by Aedes aegypti.
• Virus can also be carried by Aedes albopictus,
  which has appeared in southern U.S.
• 4 serotypes.
• Infection by a 2nd serotype often results in the
  deadly dengue hemorrhagic fever.
       Classic Dengue Fever
• First infection results in a high fever that
  lasts several days.
• Also chills, aches, weakness.

• 2009 outbreak in Key West, Florida.
  – 82 cases.
     Dengue Hemorrhagic Fever
•   Also known as Dengue Shock Syndrome.
•   Not actually hemorrhagic.
•   Plasma leaks into interstices.
•   Heavy immune response follows.
•   Often deadly.

• Vaccines are in development.
       Vaccine for Dengue?
• Must be tetra-valent.
• Must avoid Antibody-Dependent
  Enhancement (ADE).
              Marburg Virus
• Similar to Ebola.
• Recent outbreak in Angola & Uganda.
  – Dutch woman brought it home with her from Uganda
    in 2008.
    Ebola Hemorrhagic Fever
• Outbreak in Congo in 2003 – 12 cases w/9
• Outbreak in Sudan in 2004 – 17 cases, 7
• End of outbreak = 42 days with no new
  cases (twice max. incubation period)
           Ebola Virus Strains
• Zaire, Sudan, Bundibugyo.
  – Ape-to-human transmission.
  – Deadly

• Reston
  – Pig-to-human transmission in Philippines?
  – Not dangerous.
               Other Zoonoses
• Bubonic Plague (Yersinia pestis)
• Typhus (Rickettsia)

•   Yellow Fever
•   Lassa Fever
•   West Nile Fever
•   Hantavirus

• Chagas’ Disease (Trypanosoma cruzi)
• African Sleeping Sickness (Trypanosoma brucei)
• Leishmaniasis (Leishmania)

To top