1. Chapter 5 Zoonotic and Vector-borne Diseases

2. Objectives
Define what is meant by a vector-borne disease and a zoonotic disease
Discuss three human diseases transmitted by each
Discuss methods used to control vector-borne and zoonotic disease

3. Zoonosis
Refers to “an infection or infectious disease transmissible under natural conditions from vertebrate animals to humans.”

4. 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.”

5. Examples of Vectors Various species of rodents (rats and mice)
Arthropods (mosquitoes, ticks, sand flies, biting midges – “no-see-ums”)

6. Methods of Transmission
Contact with the skin
A bite or scratch from an animal
Direct inhalation or ingestion
The bite of an arthropod vector

7. Vector-Borne Diseases
Malaria
Leishmaniasis
Plague
Lyme Disease
Rocky Mountain Spotted Fever

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

9. Malaria Transmission
By mosquitoes that carry a parasite known as a plasmodium.
Transmission involves the complex life cycle of mosquitoes (the vector) and human hosts.

10. Infectious Agents of Malaria
Plasmodium falciparum
Most deadly
Plasmodium vivax
Plasmodium ovale
Plasmodium malariae

11. Symptoms of Malaria Fever and flu-like signs Vomiting and diarrhea
Jaundice (due to anemia)
Kidney failure
Seizures and coma
Death

12. The Cost of Malaria
Lost productivity, lost earnings, and negative impacts upon tourism
The direct costs include treatment and prevention of the disease (medicine, hospitalization, and pesticide use).

13. Figure 5-3 Female Anopheles gambiae mosquito feeding.
Source: Reprinted courtesy of the CDC Public Health Image Library. ID# Jim Gathany Content Provider. Available at: phil/details.asp. Accessed March 1, 2010.

14. Control of Malaria
Spraying with DDT and administering synthetic anti-malaria drugs.
Dicholor-diphenyl-tricholorethane (DDT)
Thought to be harmful to wildlife; use of DDT was opposed by many.
South Africa has used annual spraying of DDT inside of homes.

15. Leishmaniasis (Protozoa)
Cutaneous leishmaniasis is transmitted by the bite of an infected sand fly.
Source: Reprinted from CDC Public Health Image Library, ID# 352. Available at: Accessed May 28, 2005.

16. Leishmaniasis (2)
The reservoir are rodents, humans and carnivores (dogs).
Transmitted from the reservoir to the human host by a sand fly.
Endemic in a total of 82 countries (including Mediterranean and Middle East) – US Military

17. Factors Associated with Leishmaniasis
Movement of the human population into endemic areas
Increasing urbanization
Extension of agricultural projects into endemic areas
Climate change due to warming

18. Control of Leishmaniasis
Apply insecticides in dwelling areas
Use of screens on houses
Eliminate breeding areas
Destroy rodent burrows
Control domestic dogs

19. Plague
The bacterium Yersinia pestis is the infectious agent, harbored by rodents
Treated with antibiotics
Transmitted by the bite of a flea
Infects both animals and humans
May have caused the plague epidemic during the Middle Ages (the “black death”)

20. Signs of the Plague Fever and chills Headaches
Infections of lymph glands
Pneumonic plague (secondary infection)

21. Control of the Plague Keep rodents in check. Remove food sources.
Wear gloves if handling wildlife.
50-60% case fatality, if not treated.

22. Source: Reprinted from Centers for Disease Control and Prevention, Plague: CDC Plague Home Page. Available at: Accessed June 8, 2005.

23. Lyme Disease Identified in 1977 - Lyme, Connecticut
Arthritis cases among children
Caused by a bacterium Borrelia burgdorferi
Treated with antibiotics
Transmitted when humans are bitten by black-legged ticks (deer) ticks
Wear light color clothing

24. (Top) From left to right: The black-legged tick (Ixodes scapularis) adult female, adult male, nymph, and larva.
Source: Reprinted from Centers for Disease Control and Prevention. Lyme Disease. Available at: Accessed December 9, 2005.

25. Rocky Mountain Spotted Fever
Rickettsial agent is Rickettsia rickettsii
A febrile disease (fever)
Treated with antibiotics
Case fatality rate up to 25% if untreated
Transmitted by an infected tick

26. Viral Hemorrhagic Fever (VHF)
Viruses require animal host or insect host as a natural reservoir
Limited to geographic areas where host survives
Animal host reservoirs include:
rodents like the cotton rat, deer mouse, and house mouse.

27. Arthropod-Borne Viral Diseases
Also known as arboviral diseases.
A group of viral diseases caused by blood-feeding arthropod vectors
Vectors that transmit arboviruses:
Ticks, sand flies, biting midges, and mosquitoes.

28. Arboviral Encephalitides
Caused by a virus that produces an acute inflammation of:
Sections of the brain
Spinal cord
Meninges
Many forms of encephalitis:
St. Louis encephalitis
Western equine encephalitis

29. Arboviral Encephalitides (continued)
Transmitted by the bite of mosquitoes from the reservoir to a human host.
The reservoir may be wild birds and small animals.
Cost of arboviral encephalitides -$150 million/year, including:
vector control
surveillance activities

30. Symptoms of Arboviral Disease
Acute CNS [central nervous system] illness
Acute fevers of short duration, with and without an exanthum [rash]
Hemorrhagic fevers
Polyarthritis and rash of variable duration

31. West Nile Virus
Classified as a mosquito-borne arboviral disease, the agent is a Flavivirus.
Mosquitoes become infected when they feed on infected birds.
Health effects vary from no symptoms to very severe symptoms.

32. Emerging Zoonoses Zoonotic diseases caused by: new agents.
known agents that occur in locales or species that previously did not appear to be affected by these known agents.

33. Factors Affecting Emerging Zoonoses
Ecological changes:
deforestation
conversion of grasslands
irrigation
Other factors include:
migration and urbanization of humans
changes in human behavior (wars)

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

35. Examples of Emerging Zoonoses
Non-conventional agent:
Bovine spongiform encephalopathy (Mad Cow Disease)
Changes in rendering process
Viral:
Hantaviruses
Ecological/environmental changes
Increasing rodent contacts

36. Hantavirus Pulmonary Syndrome (HPS) – Rare
The causative agent is the hantavirus
family of Bunyaviridae.
Transmitted when aerosolized (airborne) by rodent urine and droppings
Primary vectors are species of rodents:
cotton rat, rice rat, white-footed mouse, and deer mouse.

37. Hantavirus Carrier
The main host for the hantavirus is the deer mouse--Peromyscus maniculatus, which is found throughout North America.
Source: Reprinted from CDC Public Health Image Library, ID# Photo credit: James Gathany. Available at: Accessed September 26, 2005.

38. Dengue Fever Caused by flaviviruses
The vector for transmission: the Aedes aegypti mosquito.
Occurs primarily in tropical areas:
Southeast Asia, Tropical Africa, and South America.
The proportion of deaths as high as 40 to 50% if untreated.

39. Symptoms of Dengue Fever
Acute fever
Headache
Muscle and joint pain
Appetite loss
Stomach problems
Rash
Hemorrhaging (shock)

40. Dengue Fever in the U.S.
Dengue fever has occurred in the continental U.S.
Southern Texas and the southeastern states at theoretical risk.
May be imported by travelers who returning from endemic tropical areas

41. Other Zoonotic Diseases
Rabies – Virus that affect CNS
Receive treatment if bitten
Anthrax - Bacterium
Inspired (breathing) is most deadly

42. Control of Mosquito-Borne Diseases
Use sentinel chickens.
Drain standing water.
Use mosquito-eating fish in ponds.
Repair window screens.
Wear repellents and protective clothing.
Spray in populated areas.

43. Travel Advisories