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 © 2012 Pearson Education, Inc.

Figure 34.1 Total Wild Domestic Year Rabies cases (thousands) © 2012 Pearson Education, Inc.

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 © 2012 Pearson Education, Inc.

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 © 2012 Pearson Education, Inc.

Figure 34.2 © 2012 Pearson Education, Inc.

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 © 2012 Pearson Education, Inc.

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 © 2012 Pearson Education, Inc.

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 © 2012 Pearson Education, Inc.

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 © 2012 Pearson Education, Inc.

II. Arthropod-Transmitted Pathogens 34.3 Rickettsial Pathogens 34.4 Lyme Disease and Borrelia 34.6 West Nile Virus © 2012 Pearson Education, Inc.

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 © 2012 Pearson Education, Inc.

34.3 Rickettsial Pathogens Typhus group –Transmitted by the body or head louse bite that gets contaminated with louse feces (Figure 34.4) © 2012 Pearson Education, Inc.

Figure 34.4 © 2012 Pearson Education, Inc.

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 © 2012 Pearson Education, Inc.

Figure –140  15 © 2012 Pearson Education, Inc.

Figure 34.6 © 2012 Pearson Education, Inc.

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) © 2012 Pearson Education, Inc.

Figure 34.9 © 2012 Pearson Education, Inc.

Figure © 2012 Pearson Education, Inc.

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 © 2012 Pearson Education, Inc.

Figure © 2012 Pearson Education, Inc.

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.

Figure © 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 © 2012 Pearson Education, Inc.

Figure © 2012 Pearson Education, Inc.