(Chapter 5) Zoonotic and Vector-borne Diseases

refers to an infection or infectious disease transmissable under natural conditions from vertebrate animals to humans
methods for transmission of zoonoses
1. contact with the skin2.

a bite or scratch from an animal3. direct inhalation or ingestion4. the bite of an arthropod vector

any insect or living carrier that transports an infectious agent from an infected individual or its wastes to a susceptible individual or its food or immediate surroundings
vector-borne diseases
–malaria–leishmaniasis–plague–Lyme disease–Rocky Mountain spotted fever
–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 Oceania–annual death toll for malaria is more than 1 million people
infectious agents of malaria
1. plasmodium falciparum (most deadly)2. plasmodium vivax3.

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plasmodium ovale4. plasmodium malariae

cost of malaria
–economic costs in Africa = $1.8 billion in 1995–lost productivity, earnings, negative impact on travel and tourism–direct costs for treatment and prevention of disease
malaria transmission
–transmitted by mosquitoes that carry a unicellular parasite known as a plasmodium–transmission involves the complex life cycle of mosquitoes (the vector) and the human hosts (with the human liver and human blood stages)
–cutaneous leishmaniasis transmitted by the bite of an infected sand fly–reservoir consists of various species of rodents–transmitted from reservoir to human host by sand fly known as the phlebotomus fly–endemic in a total of 82 countries
environmental factors associated with observed increases in Leishmaniasis
–movement of human population into endemic areas–increasing urbanization–extension of agricultural projects into endemic areas–climate change due to global warming
–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
Lyme disease
–a condition identified in 1977 when a cluster of arthritis cases occurred among children around the area of Lyme, Connecticut–causative agent is a bacterium known as Borrelia burgdorferi–transmitted by infected deer ticks
Rocky Mountain spotted fever
–causal agent is Rickettsia rickettsii, a rickettsial agent–a febrile disease–case fatality rate up to 25% among untreated patients–transmitted by the bite of an infected tick
arthropod-borne viral diseases
–also known as arboviral diseases–a group of viral diseases that are most commonly aquired when blood-feeding arthropod vectors infect a human host–vectors that transmit arboviruses include ticks, sand flies, biting midges, and mosquitoes
4 main clinical symptoms of arboviral disease
1. acute CNS (central nervous system) illness2.

acute benign fevers of short duration, with and without an exanthum (rash)3. hemorrhagic fevers4. polyarthritis and rash, with or without fever and of variable duration

Arthropod-borne viral hemorrhagic fever (VHF)
–viruses that cause VHFs require an animal host or insect host (arthropod vector) as a natural reservoir–viruses are limited to those geographic areas in which the host species survive–examples of animal host reservoirs include rodents, such as the cotton rat, deer mouse, and house mouse
Arboviral encephalitides
–caused by a virus that produces an acute inflammation of sections of the brain, spinal cord, and meninges–among the etiologic agents are viruses associated with many forms of encephalitis–transmitted by the bite of mosquitoes from the reservoir to a human host–reservoir consists of wild birds and small animals–cost is ~$150 million per year
West Nile virus
–classified as a mosquito-borne arboviral diesease, 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 severe symptomatology

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 did not previously appear to be affected by these known agents
factors associated with the rise of emerging zoonoses
1. ecological changes that result from agricultural practices (deforestation, conversion of grasslands, and irrigation)2. other factors include changes in the human population and human behavior (wars, migration, and urbanization)
Hantavirus Pulmonary Syndrome (HPS)
–causative agent is the hantavirus, part of the viral family known as Bunyaviridae–may be transmitted when aerosolized urine and droppings from infected rodents are inhaled–primary vectors are four species of rodents (cotton rat, rice rat, white-footed mouse, and deer mouse)
hantavirus carrier
main host for the hantavirus is the deer mouse–Peromyscus maniculatus–which is found throughout North America
Dengue fever
–caused by flaviviruses–vector is the Aedes aegypti mosquito–occurs primarily in tropical areas of the world (Southeast Asia, tropical Africa, and South America)–proportion of deaths can be as high as 40-50% when the disease is untreated
other zoonotic diseases

monkeypox2. tularemia3. rabies4. anthrax5. psittacosis

control of mosquito-borne diseases
1. use sentinel chickens2. drain standing water3.

introduce mosquito-eating fish into ponds4. repair window screens5. wear repellents and protective clothing