Post on 02-Jan-2016
• Zoonosis– Animal disease transmissible to humans
– Generally transmitted via direct contact, aerosols, or bites
• Diseases in animals may be either– Enzootic: present endemically in certain
populations
– Epizootic: incidences reach epidemic proportions
I. Animal-Transmitted Pathogens
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34.1 Rabies Virus
• Rabies – Occurs primarily as an epizootic disease in
animals but can be spread as a zoonotic disease to humans (Figure 34.1)
– Reservoirs in the U.S. are raccoons, skunks, coyotes, foxes, and bats
– Over 50,000 people die annually, primarily in developing countries
– Over 1,000,000 people receive postexposure prophylactic care each year
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Figure 34.1
TotalWildDomestic
Year
Ra
bie
s c
as
es (
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us
an
ds
)
10
9
8
7
6
5
4
3
2
1
01977 1982 1987 1992 1997 2002 2007
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34.1 Rabies Virus
• Rhabdovirus– A negative-strand RNA virus that causes rabies
– Infects central nervous system of warm-blooded animals
– Leads to death if not treated
– Enters the body through a wound or bite
– In humans, 9 months may pass before onset of symptoms
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34.1 Rabies Virus
• Virus proliferates in the brain and leads to fever, excitation, dilation of the pupils, excessive salivation, anxiety, and fear of swallowing
• Rabies is diagnosed using tissue samples (Figure 34.2)
• Victim can be passively immunized with rabies immune globulin– Also is immunized using a rabies virus vaccine
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34.1 Rabies Virus
• Rabies spread is prevented largely through immunization of domestic animals
• Rabies treatment strategy has been extremely successful in the U.S.– Less than 3 cases a year are reported in humans
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34.2 Hantavirus
• Hantaviruses– Cause several severe diseases
• Hantavirus pulmonary syndrome (HPS) • Hemorrhagic fever with renal syndrome (HFRS)
– Both syndromes caused by hantavirus-infected rodents
– Named for Hantaan, Korea, where the virus was first recognized as a human pathogen
– Significant outbreaks have occurred in the U.S.• Arizona, Colorado, and New Mexico in 1993
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34.2 Hantavirus
• Hantavirus is a member of the Bunyaviridae, enveloped, segmented, negative-strand RNA viruses (Figure 34.3)
– Related to hemorrhagic fever viruses such as Lassa fever and Ebola
• Infections are handled with BSL-4 safety precautions
• Infect rodents including mice, rats, voles, and lemmings
• Up to 200,000 cases are recognized annually• Transmitted by inhalation of virus-contaminated
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34.2 Hantavirus
• Hantavirus pulmonary syndrome (HPS)– Characterized by a sudden onset of fever,
myalgia, thrombocytopenia, leukocytosis, and pulmonary capillary leakage
– Death occurs within several days in 35% of cases
– No virus-specific treatment or vaccine for hantaviruses
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II. Arthropod-Transmitted Pathogens
• 34.3 Rickettsial Pathogens• 34.4 Lyme Disease and Borrelia• 34.6 West Nile Virus
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34.3 Rickettsial Pathogens
• Rickettsias are small bacteria that have strict intracellular existence in vertebrates
– Associated with bloodsucking arthropods
– Three groups: (1) typhus group, (2) spotted fever group, and (3) ehrlichiosis group
– Named for Howard Ricketts
– Closely related to human mitochondria
– Contain minimal sets of genes required for intracellular dependency
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34.3 Rickettsial Pathogens
• Typhus group– Transmitted by the body or head louse bite
that gets contaminated with louse feces (Figure 34.4)
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34.3 Rickettsial Pathogens
• Spotted fever group– Transmitted by dog and wood ticks
– Over 2,000 people acquire the disease every year (Figure 34.5)
– Rickettsia grow in nucleus and cytoplasm (Figure 34.6)
– Symptoms include headache, fever, and rash
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34.4 Lyme Disease and Borrelia
• Lyme disease– Affects humans and other animals
– Old Lyme, Connecticut, was where cases were first recognized
– Most prevalent tickborne disease in the U.S.
– Caused by the spirochete Borrelia burgdorferi (Figure 34.9)
– Spread primarily by the deer tick (Figure 34.10)
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34.4 Lyme Disease and Borrelia
• Deer and white-footed field mouse are the prime mammalian reservoirs
• Also identified in Europe and Asia• In U.S., most cases reported in the Northeast
and upper Midwest (Figure 34.11)• Number of Lyme disease cases rising yearly
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34.4 Lyme Disease and Borrelia
• Symptoms of Lyme disease include headache, backache, chills, and fatigue
• In 75% of cases a large rash occurs at the site of the tick bite (Figure 34.12)
• During the initial stages it can be treated with antibiotics
• Chronic stage develops in weeks to months– 40–60% of these patients develop arthritis
– Others develop neurological damage or heart damage
– No toxins or virulence factors have been identified© 2012 Pearson Education, Inc.
34.6 West Nile Virus
• West Nile fever caused by West Nile virus (WNV)– Transmitted by mosquito bites (Figure 34.17)
– Transmission of WNV is seasonal
– At least 130 species of birds are WNV reservoirs
– Humans and other animals are dead-end hosts
– No antiviral drugs are effective in vivo against WNV
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