1. Chapter 5 Zoonotic and Vector-borne Diseases February 18, 2010

2. Zoonosis An infection or infectious disease transmissible under natural conditions from vertebrate animals to humans Methods for Transmission: –Contact with the skin –Bite or scratch from an animal –Direct inhalation or ingestion –Bite of an arthropod vector

3. Vector An insect or any living carrier that transports an infectious agent from an infected individual or its wastes to a susceptible individual or its food or immediate surroundings Examples: –Rodents (rats and mice) –Arthropods (mosquitoes, ticks, sand flies, biting midges)

4. Vector-Borne Diseases Malaria Leishmaniasis Plague Lyme disease Rocky Mountain spotted fever West Nile Virus

5. Other Zoonotic Diseases Monkeypox Tularemia Rabies Anthrax Psittacosis

6. Malaria Found in more than 100 countries > 40% of the world’s population at risk Endemic regions: –Central and South America –Africa –India –Southeast Asia –Middle East – Oceania Annual death toll > than 1 million persons

7. The Cost of Malaria Economic costs in Africa estimated at $1.8 billion in 1995 Lost productivity, lost earnings, and negative impacts upon travel and tourism Direct costs: –Treatment of the disease (medicine, hospitalization) – Prevention (pesticide use)

8. Malaria Transmission Transmitted by mosquitoes that carry a unicellular parasite known as a plasmodium. –Plasmodium falciparum (Most deadly) –Plasmodium vivax –Plasmodium ovale –Plasmodium malariae Transmission involves the complex life cycle of mosquitoes (the vector) and human hosts (with human liver and human blood stages).

9. Female Anopheles gambiae mosquito feeding Source: Reprinted from CDC Public Health Image Library, ID# 1662. Available at: http://phil.cdc.gov/phil/details.asp. Accessed May 27, 2005. http://phil.cdc.gov/phil/details.asp

10. Life cycle of the parasites that are causal agents of malaria Source: Reprinted from CDC Public Health Image Library, ID# 3405. Available at: http://phil.cdc.gov/phil/details.asp. Accessed May 27, 2005.http://phil.cdc.gov/phil/details.asp

11. What Can Be Done to Control Malaria? During mid-20 th century, malaria was all but eliminated in many countries due to the use of pesticides, particularly DDT. Thought to be harmful to wildlife, outdoor spraying of DDT was discontinued in many developed countries. Some countries now permit the spraying of DDT inside of homes.

12. Leishmaniasis Cutaneous leishmaniasis is transmitted by the bite of an infected sand fly. Source: Reprinted from CDC Public Health Image Library, ID# 352. Available at: http://phil.cdc.gov/phil/details.asp. Accessed May 28, 2005.http://phil.cdc.gov/phil/details.asp

13. Leishmaniasis Reservoir for the cutaneous form of leishmaniasis = rodents. Disease is transmitted from the reservoir to the human host by a sand fly (phlebotomus fly) Endemic in a total of 82 countries

14. Environmental Factors Associated with Leishmaniasis Movement of humans into endemic areas Urbanization Extending agriculture into endemic areas Climate change due to global warming

15. Plague Infectious agent = Bacterium Yersinia pestis Condition that infects both animals and humans Transmitted by flea bites harbored by rodents Plague epidemic during the Middle Ages (the “black death”) was caused by fleas from infested rats

16. Source: Reprinted from Centers for Disease Control and Prevention, Plague: CDC Plague Home Page. Available at: http://www.cdc.gov/ncidod/dvbid/plague/index.htm. Accessed June 8, 2005. http://www.cdc.gov/ncidod/dvbid/plague/index.htm

17. Lyme Disease Condition identified in 1977 from a cluster of arthritis cases in children from Lyme, Connecticut. Causative agent = bacterium Borrelia burgdorferi. Disease transmitted when infected deer ticks bite human beings.

18. Source: Reprinted from Centers for Disease Control and Prevention. Lyme Disease. Available at: http://www.cdc.gov/ncidod/dvbid/lyme/ld_transmission.htm. Accessed December 9, 2005. http://www.cdc.gov/ncidod/dvbid/lyme/ld_transmission.htm

19. Rocky Mountain Spotted Fever Causal agent = Rickettsia rickettsii –a rickettsial agent. Febrile disease (causes fever) Case fatality rate = 25% among untreated patients Transmitted by the bite of an infected tick

20. Arthropod-Borne Viral Diseases Also known as arboviral diseases. Viral diseases acquired when blood- feeding arthropod vectors infect a human host. Vectors that transmit arboviruses: –Ticks –Sand flies –Biting midges –Mosquitoes

21. Clinical Symptoms of Arboviral Disease 1.Acute Central Nervous System illness 2.Acute benign fevers 3.Rash 4.Hemorrhagic fevers 5.Polyarthritis

22. Arthropod-Borne Viral Hemorrhagic Fever (VHF) Viruses require an animal host or insect host as a reservoir –rodents (deer mouse, and house mouse) Viruses are limited to areas in which the host survives

23. Arboviral Encephalitides Caused by virus Produces acute inflammation of: –Sections of the brain –Spinal cord –Meninges Etiologic agents are viruses associated with encephalitis: –St. Louis encephalitis –Western equine encephalitis

24. Arboviral Encephalitides Transmitted by bite of mosquitoes from reservoir to a human host. Reservoir for encephalitis are wild birds and small animals. Cost = ~$150 million per year –vector control –surveillance

25. West Nile Virus Mosquito-borne arboviral disease Etiologic agent = Flavivirus Mosquitoes = carriers that become infected when they feed on infected birds Health effects vary from nothing to very severe illness

26. Emerging Zoonoses Zoonotic diseases caused by either new agents or by known agents Occur in locales or species that previously did not appear to be affected by these known agents

27. Factors Associated with the Rise of Emerging Zoonoses Ecological changes that result from agriculture: –Deforestation –Conversion of grasslands –Irrigation Changes in the human population & behavior –Wars –Migration –Urbanization

28. Emerging Zoonoses and Contributing Factors Bacterial: –Escherichia coli O157:H7 (hemolytic-uremic syndrome) Mass food processing technology allowing contamination of meat Parasitic: –Cryptosporidium Contaminated surface water, faulty water purification

29. Emerging Zoonoses and Contributing Factors Non-conventional agent: –Bovine spongiform encephalopathy Changes in meat rendering process Viral: –Hantaviruses Ecological/environmental changes Increasing rodent contacts

30. Hantavirus Pulmonary Syndrome (HPS) Causative agent = hantavirus –part of the viral family Bunyaviridae Transmitted by inhalation –aerosolized urine and droppings from infected rodents are inhaled Primary vectors = rodents –cotton rat, rice rat, white-footed mouse, and deer mouse.

31. Hantavirus Carrier Host = deer mouse (Peromyscus maniculatus) Found throughout North America. Source: Reprinted from CDC Public Health Image Library, ID# 1183. Photo credit: James Gathany. Available at: http://phil.cdc.gov/Phil/details.asp. Accessed September 26, 2005. http://phil.cdc.gov/Phil/details.asp. Accessed September 26

32. Dengue Fever Caused by flaviviruses Vector = Aedes aegypti mosquito. Occurs in tropical areas –Southeast Asia –Tropical Africa –South America. Deaths can be as high as 40 to 50% when the disease is untreated.

33. Dengue Fever in the U.S. Dengue fever has been documented in the continental U.S. –Southern Texas and the southeastern states are at risk for transmission of dengue and sporadic outbreaks –Virus may be imported into the U.S. by travelers returning from endemic areas

34. Control of Mosquito-Borne Diseases Use sentinel chickens. Drain standing water. Introduce mosquito-eating fish into ponds. Repair window screens. Wear repellents and protective clothing.