Zoonosis –Animal disease transmissible to humans –Generally transmitted via direct contact, aerosols, or bites Diseases in animals may be either –Enzootic:

• 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

© 2012 Pearson Education, Inc.

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


Figure 34.1

TotalWildDomestic

Year

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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


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


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


Figure 34.2


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


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


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

rodent excreta© 2012 Pearson Education, Inc.

Figure 34.3


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


II. Arthropod-Transmitted Pathogens

• 34.3 Rickettsial Pathogens• 34.4 Lyme Disease and Borrelia• 34.6 West Nile Virus


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



• Typhus group– Transmitted by the body or head louse bite

that gets contaminated with louse feces (Figure 34.4)


Figure 34.4



• 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


Figure 34.5

1–140 15


Figure 34.6


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)


Figure 34.9


Figure 34.10



• 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


Figure 34.11



• 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.

Figure 34.12


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


Figure 34.17


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Zoonosis –Animal disease transmissible to humans –Generally transmitted via direct contact, aerosols, or bites Diseases in animals may be either –Enzootic: