(e.g., medicine, hospitalization, and pesticide use).
1. Chapter 5Chapter 5
2. Learning ObjectivesLearning Objectives
By the end of this chapter the reader will be able to:
• Discuss the impact of human environmental change
on emerging infectious diseases in animals and man
• Indicate how a disease may be transmitted from an
animal reservoir to humans
• Define what is meant by a vector-borne disease and
a zoonotic disease
• List three human diseases transmitted by arthropod
vectors and three caused by zoonoses
• Discuss methods used to control vector-borne and
• 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
5. Bacterial ShapesBacterial Shapes
6. Bacteria vs. VirusBacteria vs. Virus
• 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.”
o Various species of rodents (rats and mice)
o Arthropods (mosquitoes, ticks, sand flies, biting midges)
8. Vector-Borne DiseasesVector-Borne Diseases
• Generally spread by blood feeding vectors
• Increased through environmental factors
o Lyme disease
o Rocky Mountain spotted fever
• A disease found in more than 100 countries, with more
than 40% of the world’s population at risk
• Endemic regions include Central and South America,
Africa, India, Southeast Asia, the Middle East, and
• Annual death toll for malaria is more than 1 million
• 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
• Principle vector for malaria is the Anopheles
mosquito which carry a plasmodium (unicellular
• Involves the complex life cycle of mosquitoes (the
vector) and human hosts (with human liver and
human blood stages).
Figure 5-3Figure 5-3 FemaleFemale AnophelesAnopheles
gambiaegambiae mosquito feeding.mosquito feeding.
• Fever and flu-like symptoms such as
headaches, muscle aches, fatigue,
and shaking chills
o 9 to 14 days after bite of an infected
o Life-cycle Figure 5-4
• Other symptoms to follow can be
jaundice, kidney failure, seizures,
mental confusion, coma, and
12. Figure 5-4Figure 5-4 The life cycle of the parasites of the genusThe life cycle of the parasites of the genus PlasmodiumPlasmodium, causal agents of malaria., causal agents of malaria.
13. Control of MalariaControl 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
• South Africa has (and to some extent still) used
annual spraying of DDT inside of homes.
• 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.
• 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
• The bacterium Yersinia pestis is the infectious agent
for plague, a condition that infects both animals
• Transmitted by the bite of a flea harbored by
• Historians believe that the plague epidemic during
the Middle Ages (the “black death”) was caused
by fleas from infested rats.
18. Source: Adapted and reprinted from the Centers for Disease Control and Prevention. Plague: CDC Plague Home Page.
Available at: http://www.cdc.gov/ncidod/dvbid/plague/index.htm. Accessed February 28, 2010.
Figure 5-14 World distribution of plague, 1998.
• Once transmitted to humans, it can progress in
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 DiseaseLyme Disease
• A condition identified in 1977 when a cluster of arthritis
cases occurred among children around the area of
• The causative agent for the disease is a bacterial
spirochete known as Borrelia burgdorferi.
• 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
21. Figure 5-16Figure 5-16 (Top) From left to right: The black-legged tick adult(Top) From left to right: The black-legged tick adult
female, adult male, nymph, and larva.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 5-17Figure 5-17 Number of reported cases of Lyme Disease byNumber of reported cases of Lyme Disease by
county – United States 2007county – United States 2007
23. Treatment and PreventionTreatment and Prevention
o Red, expanding rash called
erythema migrans (EM)
o Fatigue, chills, fever,
headache, muscle and
joint aches, and swollen
• 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 SpottedRocky Mountain Spotted
• Causal agent is Rickettsia rickettsii, a rickettsial
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
o Much lower when treated early with antibiotics
25. Viral Hemorrhagic Fevers (VHF)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
• The viruses are limited to those geographic areas in
which the host species reside.
26. Arthropod-Borne ViralArthropod-Borne Viral
Diseases (Arboviral)Diseases (Arboviral)
• A group of viral diseases that can be acquired
when blood-feeding arthropod vectors infect a
• 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
27. Arboviral EncephalitidesArboviral Encephalitides
• Caused by a virus that produces an acute
o Sections of the brain
o Spinal cord
• Transmitted by the bite of an arthropod vector
• Cost of arboviral encephalitides is approximately
$150 million per year, including vector control and
28. West Nile VirusWest 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.
• Health effects vary from no symptoms to very
o Onset between 3 and 14 days
o In severe cases, neurological effects can be permanent
29. West Nile Virus - 2009West Nile Virus - 2009
30. Emerging ZoonosesEmerging 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
o Other factors include changes in the human population
and human behavior
31. Figure 5-20: Range and recognized site(s) of origin of a variety of emerging and
v-CJD = variant Creutzfeldt-Jakob disease; E. coli = Escherichia coli.
32. Hantavirus PulmonaryHantavirus Pulmonary
Syndrome (HPS)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. Figure 5-24: Hantavirus pulmonary syndrome (HPS) cases, by state of residence.
34. Dengue FeverDengue Fever
• Caused by four flaviviruses that create illness that
range from mild to severe
o Dengue fever, Dengue Hemorrhagic Fever, and Dengue
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
35. Dengue Fever in the U.S.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
• Southern Texas and the southeastern states are at
theoretical risk for transmission of dengue and for
• The dramatic global resurgence is due to lack of
effective mosquito control, population growth, and
poor treatment of water and human waste.
36. Ebola Hemorrhagic FeverEbola 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
37. Rift Valley FeverRift 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.
38. Other Notable Zoonotic DiseasesOther Notable Zoonotic Diseases
o Contracted through a bite or direct contact with the
infected animal’s blood, body fluids, or lesions
o Potentially serious illness that occurs naturally in the
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
39. Other Notable Zoonotic DiseasesOther Notable Zoonotic Diseases
o A highly fatal disease of the CNS caused by a virus that is
transmitted through the bite of an affected animal.
o Worldwide, dog bites are the principal source to humans.
o In the U.S., most case are associated to wild animals (bats,
raccoons, and skunk)
o 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
o 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
40. Other Notable Zoonotic DiseasesOther Notable Zoonotic Diseases
o Anthrax is a serious disease caused by Bacillus anthracis, a
bacterium that forms spores
o There are three types of anthrax:
• skin (cutaneous)
• lungs (inhalation)
• digestive (gastrointestinal)
o All three forms are treatable
with antibiotics administered
as soon as possible after
o Symptoms can be mild , and
if ignored, become severe
and death ensues
41. Other Notable Zoonotic DiseasesOther 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
• The emergence of a new and very different influenza
virus to infect people can cause an influenza
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.
42. Control of Mosquito-BorneControl of Mosquito-Borne
• Use sentinel chickens to monitor for presence of
• Drain standing water.
• Introduce mosquito-eating fish into ponds.
• Wear repellents and protective clothing.
• Repair window screens.
43. Figure 5-35: Check forFigure 5-35: Check for AedesAedes mosquito breeding in your homemosquito breeding in your home