Zoonotic and Vector Borne Disease

1. Chapter 5
Zoonotic and
Vector-Borne Diseases

2. Learning Objectives
By the end of this chapter the reader will be able to:
• Provide a rationale for environmental change and
infectious disease occurrence
• Indicate how a disease may be transmitted from an
animal reservoir to humans
• Define the terms vector-borne and zoonotic diseases,
giving examples
• List three human diseases transmitted by arthropod
vectors
• 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.”
• Methods of transmission:
o Contact with the skin
o A bite or scratch from an animal
o Direct inhalation or ingestion
o The bite of an arthropod vector
• See Table 5-2 for examples

4. Zoonosis

5. Bacterial Shapes
Bacteria get
part of their
name from their
shape and
interaction with
other bacteria.

6. Bacteria vs. Virus
A virus is
harder to deal
with because
it is much
smaller and
invades
healthy cells
to use as a
host.

7. Vector
• Defined as “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
o Various species of rodents (rats and mice)
o Arthropods (mosquitoes, ticks, sand flies, biting midges)

8. Vector-Borne Diseases
• Generally spread by blood feeding vectors (Biological
transmission)
• Increased through environmental factors
• Examples (details in the following slides):
o Malaria
o Leishmaniasis
o Plague
o Lyme disease
o Rocky Mountain spotted fever

9. Malaria
• A disease found in more than 100 countries, with more
than 50% of the world’s population at risk
• Endemic regions include Central and South America,
Africa, India, Southeast Asia, the Middle East, and
Oceania.
• Annual death toll for malaria is more than 1 million
persons.
• Global direct economic costs incurred by malaria are
estimated to be $12 billion U.S. annually
o The direct costs include those for treatment and prevention of
the disease
o Lost productivity, lost earnings, and negative impacts upon
travel and tourism

10. Transmission
• Principle vector for malaria is the Anopheles mosquito
which carry a plasmodium (unicellular parasite)
• Involves the complex life cycle of mosquitoes (the
vector) and human hosts (with human liver and human
blood stages).
Figure 5-3 Female Anopheles
gambiae mosquito feeding.

11. Symptoms
• Fever and flu-like symptoms such as
headaches, muscle aches, fatigue, and
shaking chills
o 9 to 14 days after bite of an infected
mosquito
o Life-cycle Figure 5-4
• Other symptoms to follow can be
jaundice, kidney failure, seizures,
mental confusion, coma, and ultimately
death.

12. Figure 5-4 The life cycle of the parasites of the genus Plasmodium, causal agents of malaria.

13. Control of Malaria
• During mid-20th century, efforts to control malaria by
spraying with DDT and administering synthetic
antimalaria drugs were found to be effective.
• Thought to be harmful to wildlife; use of DDT was
opposed by many developed nations, especially the U.S.
• South Africa has (and to some extent still) used annual
spraying of DDT inside of homes.
• Other control methods are to use bed nets and control
areas with standing water to reduce breeding grounds

14. Leishmaniasis
• The reservoir for the cutaneous form of leishmaniasis
includes wild rodents, human beings, and carnivores
(e.g., domestic dogs).
• Transmitted from the reservoir to the human host by a
sand fly known as the phlebotomus fly.

15. Transmission
• Caused by the transmission of a protozoal organism that
exist in two forms
o Promastigotes and amastigotes
• Present in the countries around the Mediterranean and
endemic in a total of 82 countries
• The annual incidence is around 600,000
• The reason for increasing cases are:
o Movement of the human population into endemic areas
o Increasing urbanization
o Extension of agricultural projects into endemic areas
o Climate change due to global warming

16. Transmission

17. Plague
• The bacterium Yersinia pestis is the infectious agent for
plague, a condition that infects both animals and
humans.
• Transmitted by the bite of a flea harbored by rodents.
• Historians believe that the plague epidemic during the
Middle Ages (the “black death”) was caused by fleas
from infested rats.

18. Figure 5-14 World distribution of reported plague
cases by country, 2000-2009.
Modified and reproduced from Centers for Disease Control and
Prevention. Plague. Maps and statistics. Available at:
https://www.cdc.gov/plague/maps/index.html.
Accessed January 29, 2017.
* Data reported to World Health Organization (WHO).
** Dot placed in center of reporting country.

19. Plague
• Etiology
• Once transmitted to humans, it can progress in stages
o Bubonic plague – fever, chills, headache
o Lymphandenitis – infected lymph nodes
o Pneumonic plague – communicable through respiratory droplets
• Untreated bubonic plague has a fatality rate from about
50 – 60%
• Controlled by mainly public awareness and controlling
the rodent population

20. Lyme Disease
• A condition identified in 1977 when a cluster of arthritis cases
occurred among children around the area of Lyme, Connecticut.
• The causative agent for the disease is a bacterial spirochete
known as Borrelia burgdorferi (image below).
• Transmission of Lyme disease to humans is associated with
infected black-legged ticks (Ixodes scapularis) that ingest blood
by puncturing the skin of the host
• A total of 28,453 confirmed
cases were reported to the
CDC in 2015. Most in the
Northeast (see map)

21. Figure 5-16 (Top) From left to right: The black-legged tick adult
female, adult male, nymph, and larva.
Source: Adapted and reprinted from the Centers for Disease Control and Prevention. Lyme Disease. Available at:
http://www.cdc.gov/ncidod/dvbid/lyme/ld_transmission.htm. Accessed March 14, 2010.

22. Figure 5-17 Number of reported cases of Lyme Disease by
county – United States 2007

23. Treatment and Prevention
• Signs
o Red, expanding rash called
erythema migrans (EM)
o Fatigue, chills, fever,
headache, muscle and joint
aches, and swollen lymph
nodes
• Antibiotic therapy exists for cases that are caught early
• Preventative measures:
o Take caution when clearing brush or landscaping
o Be aware when you are in areas that ticks inhabit
o Wear light colored clothing and inspect yourself after leaving an
outdoor area

24. Rocky Mountain Spotted Fever
• Causal agent is Rickettsia rickettsii, a rickettsial agent.
o Transmitted by the bite of an infected American dog tick or
Rocky Mountain wood tick
• A febrile disease with sudden onset of high fevers that
may last up to 3 weeks.
• Case fatality rate can range up to 25% among untreated
patients
o Much lower when treated early with antibiotics

25. Viral Hemorrhagic Fevers (VHF)
• Viruses that cause VHFs require an animal host or insect
host (arthropod vector) as a natural reservoir.
• Examples of animal host reservoirs include rodents such
as the cotton rat, deer mouse, and house mouse.
• The viruses are limited to those geographic areas in
which the host species reside.
Examples of VHFs discussed in this chapter are:
o Hantavirus pulmonary syndrome (see emerging zoonoses)
o Dengue hemorrhagic fever (covered in the section on emerging and
reemerging infections)

26. Arthropod-Borne Viral
Diseases (Arboviral)
• A group of viral diseases that can be acquired when
blood-feeding arthropod vectors infect a human host.
• Vectors that transmit arboviruses include ticks, sand
flies, biting midges, and mosquitoes.
Four Main Clinical Symptoms of Arboviral Disease
1. Acute CNS [central nervous system] illness
2. Acute self-limited fevers, with and without exanthum [rash]
3. Hemorrhagic fevers
4. Polyarthritis and rash, with or without fever and of variable duration

27. Arboviral Encephalitides
• Caused by a virus that produces an acute
inflammation of:
o Sections of the brain
o Spinal cord
o Meninges
• Transmitted by the bite of an arthropod vector (primarily
mosquitoes, midges, and sandflies)
• The reservoir hosts for some forms of encephalitis
viruses consist of nonhuman vertebrate hosts (e.g., wild
birds and small animals).
• Cost of arboviral encephalitides is approximately $150
million per year, including vector control and surveillance
activities.

28. West Nile Virus
• Classified as a mosquito-borne arboviral fever, the
etiologic agent is a Flavivirus.
• Mosquitoes are the carriers that become infected when
they feed on infected birds.
o See geographical map on page 113 for areas of reported cases
• Health effects vary from no symptoms to very severe
symptomatology.
o Onset between 3 and 14 days
o In severe cases, neurological effects can be permanent
• See Fact Sheet on page 111

29. Emerging Zoonoses
• Refers to zoonotic diseases that are caused by either
apparently new agents or by known agents that occur in
locales or species that previously did not appear to be
affected by these known agents.
• Factors in the rise of emerging zoonoses
o Ecological changes that result from agricultural practices
• Deforestation
• Conversion of grasslands
• Irrigation
o Other factors include changes in the human population and
human behavior (e.g., wars, migration, and urbanization)

30. Figure 5-21: Range and recognized site(s) of origin of a variety of emerging and
re-emerging infections.
v-CJD = variant Creutzfeldt-Jakob disease; E. coli = Escherichia coli.

32. Hantavirus Pulmonary
Syndrome (HPS)
• The causative agent is the hantavirus, part of the viral family
known as Bunyaviridae.
• May be transmitted when aerosolized (airborne) urine and
droppings from infected rodents are inhaled.
• Highly fatal condition transmitted mainly from four species of
rodents: cotton rat, rice rat, white-footed mouse, and deer
mouse.
The main host for the hantavirus is the deer
mouse--Peromyscus maniculatus, which is
found throughout North America.

33. Dengue Fever
• Caused by four flaviviruses that create illness that range
from mild to severe
o Dengue fever, Dengue Hemorrhagic Fever, and Dengue Shock
Syndrome
o The proportion of deaths can be as high as 40% to 50% when
the disease is untreated.
• Occurs primarily in tropical subtropical areas of the
world, for example, Southeast Asia, tropical Africa, and
South America. (figure 5-25)
• The vector for transmission is
the Aedes aegypti mosquito.
o Resurged after the ban on DDT

34. FIGURE 5.25 World distribution of dengue—2008.

35. Dengue Fever in the U.S.
• In the U.S., most cases of dengue are imported by
travelers who are returning from endemic areas or by
immigrants.
o However, occurrence of dengue fever that originated in the
continental U.S. has been documented.
• Southern Texas and the southeastern states are at
theoretical risk for transmission of dengue and for
sporadic outbreaks.
• The dramatic global resurgence is due to lack of
effective mosquito control, population growth, and poor
treatment of water and human waste.

36. Zika Virus
• Zika is spread mostly by the bite of an infected Aedes
species mosquito (Ae. aegypti and Ae. albopictus).
These mosquitoes bite during the day and night.
o Research has also shown that the virus can be spread through sexual contact
and blood transfusions (figure 5.27)
• Most won’t have symptoms but some may develop a
rash and a fever.
• Greater risks are with pregnant mothers who can pass it
along to a developing fetus which can cause
microcephaly and other congenital defects.
• Top 5 things you need to know about Zika
o https://www.cdc.gov/zika/pdfs/Top5.pdf

37. Ebola Hemorrhagic Fever
• Severe, often-fatal disease in humans and nonhuman
primates (monkeys, gorillas, and chimpanzees) that has
appeared sporadically since its initial recognition in 1976.
• Incubation period for Ebola HF ranges
from 2 to 21 days
o Onset of illness is abrupt and is
characterized by fever, headache, joint and
muscle aches, sore throat, and weakness,
followed by diarrhea, vomiting, and
stomach pain.
o A rash, red eyes, hiccups and internal and
external bleeding may be seen in some
patients.
Ebola virus in the blood

38. Rift Valley Fever
• An acute, fever-causing viral disease that affects
domestic animals (such as cattle, buffalo, sheep, goats,
and camels) and humans.
• Humans can get RVF as a result of bites from
mosquitoes or they are exposed to either the blood or
other body fluids of infected animals
• Patents have either no symptoms or a
mild illness associated with fever and
liver abnormalities. However, in some
patients the illness can progress to
hemorrhagic fever, encephalitis, or
ocular disease.

39. Other Notable Zoonotic Diseases
• Monkeypox
o Rare
o Contracted through a bite or direct contact with the infected
animal’s blood, body fluids, or lesions
• Tularemia
o Potentially serious illness that occurs naturally in the United
States.
o It is caused by the bacterium Francisella tularensis found in
animals (especially rodents, rabbits, and hares).
o Also, can be contracted by consuming water or food that is
contaminated with the bacterium

40. Other Notable Zoonotic Diseases
Rabies
• A highly fatal disease of the CNS caused by a virus that is
transmitted through the bite of an affected animal.
• Worldwide, dog bites are the principal source to humans.
Rare now in the U.S.
• In the U.S. after 1960 and the vaccination program, most case
are now associated to wild animals (bats, raccoons, and
skunk) Figure 5.33
• Early symptoms include irritability, headache, fever and
sometimes itching or pain at the site of exposure. The disease
eventually progresses to paralysis, spasms of the throat
muscles, convulsions, delirium and death
Treatment
• vaccine is usually given in the upper arm for a total of 5
injections over a period of 28 days along with a one time dose
of rabies immune globulin for immediate temporary immunity

41. Other Notable Zoonotic Diseases
• Anthrax
o Anthrax is a serious disease caused by Bacillus anthracis, a
bacterium that forms spores
o There are three types of anthrax:
• skin (cutaneous), less fatal
• lungs (inhalation), high fatality
• digestive (gastrointestinal), rare
o All three forms are treatable with
antibiotics administered as soon
as possible after exposure
o Symptoms can be mild , and if
ignored, become severe and death
ensues

42. Other Notable Zoonotic Diseases
• The three types of Influenza viruses are
o Human influenza A and B viruses cause seasonal epidemics of
disease almost every winter in the United States.
• The emergence of a new and very different influenza virus to
infect people can cause an influenza pandemic.
o Influenza A can infect a variety of animals, but certain strains can
be specific to certain species
o Influenza type C infections cause a mild respiratory illness and
are not thought to cause epidemics.

43. Control of Mosquito-Borne
Diseases
• Use sentinel chickens and birds to monitor for presence
of viruses.
• Drain standing water.
• Introduce mosquito-eating
fish into ponds.
• Wear repellents and
protective clothing.
• Repair window screens. FIGURE 5.35 Sentinel birds
used to monitor for mosquito-
borne viruses.

44. Check for Aedes mosquito breeding in your home

45. 1. Genetics
2. Our behavior
1. Lifestyle
2. Medical Care
3. Our environment
Factors affect health and longevity
We have control over 84% of disease vulnerability

46. Control Spread of Disease
 Understanding pathogen means of survival
helps us learn how to control them
 Favorable O2 supply
◦ Aerobic versus anaerobic
◦ Facultative bacteria tolerate a range of O2 levels
◦ Manipulate O2 concentrations to destroy them
 Temperature requirements
◦ Thermophilic ,Mesophilic Psychrophilic
◦ Keep it hot, keep it cold, or don’t keep it long!

47. Control Spread of Disease
 Nutrition
◦ Keep utensils and surfaces clean (high heat)
 Moisture
◦ Need water to survive
◦ Keep dry food packages tightly sealed
 Unfavorable pH
◦ Prefer neutral, around 7.0
 Change osmotic pressure
◦ Isotonic, Hypotonic, Hypertonic
◦ Reason why most foods have high sodium content
to preserve its shelf life

48. Control Spread of Disease
 Absence of toxic materials
◦ As with most organisms, the introduction of a toxic
substance prevents its growth or destroys its cell
membrane
 Space
◦ Microbes divide rapidly in the proper environment
◦ Without proper space, toxins buildup and can kill
off the colony

49. Defense against disease
• First line of defense
o Prevention; knowledge of disease
• Second line of defense
o Skin
o Mucous membranes
o Nutrition

50. Defense against disease
• Third line of defense
o Cellular defense (phagocytosis)
o Active Immunity
• Production of antibodies
o Passive immunity
• Required antibodies are introduced into the body
• Natural or Artificial
• Fourth line of defense
o Curative medicine