Chapter 5 Flashcards
Zoonosis
•“An infection or infectious disease transmissible under natural conditions from vertebrate animals to humans”
Methods for Transmission of Zoonoses
- Contact with the skin
- Bite or scratch of an animal
- Direct inhalation or ingestion
- Bite of an arthropod vector
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 of Vectors
•Various species of rodents
–Rats and mice
•Arthropods
–Mosquitoes
–Ticks
–Sand flies
Biting midges
Vector-Borne Diseases
- Malaria
- Leishmaniasis
- Plague
- Lyme disease
- Rocky Mountain spotted fever
Malaria
•Found in more than 100 countries
–More than 40% of the world’s population at risk
•Endemic regions
–Central and South America
–Africa, Middle East
–India, Southeast Asia
–Oceania
•Annual death toll: more than 1 million persons
Infectious Agents of Malaria
•Plasmodium falciparum
–Most deadly
- Plasmodium vivax
- Plasmodium ovale
- Plasmodium malariae
Figure 05.F02: Ronald Ross, one of the discoverers of the malaria parasite.
Cost of Malaria
- Estimated global direct economic costs: $12 billion US annually
- Direct costs
–Treatment (e.g., hospitalization, medicine)
–Disease prevention (e.g., medicine, pesticide use)
•Other costs
–Lost productivity
–Lost earnings
–Negative impact on tourism and agricultural labor
Malaria Transmission
- Involves complex life cycle of mosquitoes (the vector) and human hosts (with human liver and human blood stages)
- Transmitted through the bite of an infected mosquito of the anopheles type
Figure 5.3 Female Anopheles gambiae mosquito feeding.
Figure 5.4 The life cycle of the malaria parasite (Plasmodium spp.)
Figure 05.F01: The edema exhibited by this African child was brought on by nephrosis associated with malaria (1975).
What Can Be Done to
Control Malaria?
- Use of DDT and synthetic antimalaria drugs found to be efficacious in the mid-20th century
- DDT use opposed by many developed nations, especially the US
–Thought to be harmful to wildlife
•South Africa has used annual spraying of DDT inside of homes.
Figure 05.F05: A Stearman bi-plane spraying an insecticide during malaria control operations in Savannah, GA.
Figure 05.F06: In 1958, the National Malaria Eradication Program used an entirely new approach, implementing DDT for spraying of mosquitoes.
Figure 05.F07: US soldier is demonstrating DDT hand spraying equipment while applying the insecticide.
Figure 5.9 Skin ulcer due to leishmaniasis; the hand of Central American adult.
•Cutaneous leishmaniasis is transmitted by the bite of an infected sand fly.
•Cutaneous leishmaniasis is transmitted by the bite of an infected sand fly.
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 (phlebotomus fly)
- Endemic in 82 countries
Figure 05.F10: This is a female Phlebotomus sp. sand fly, a vector of the parasite responsible for leishmaniasis.
Figure 05.F11: This is an illustration of the life cycle of Leishmania spp., the causal agents of leishmaniasis
Environmental Factors Associated with Observed Increases in Leishmaniasis
- Movement of the human population into endemic areas
- Increasing urbanization
- Extension of agricultural projects into endemic areas
- Climate change due to global warming
Plague
•Infectious agent: bacterium Yersinia pestis
–Infects both animals and humans
•Transmission: 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
Figure 05.F13: Male Xenopsylla cheopis (oriental rat flea) engorged with blood. This flea is the primary vector of plague in most large plague epidemics in Asia, Africa, and South America.
Figure 5.15 Worldwide distribution of reported* plague cases by country, 2000–2009.
Figure 05.F16: Borrelia burgdorferi, the spirochetal bacteria that cause Lyme disease.
Figure 5.17 (Top) From left to right: The black-legged tick (Ixodes scapularis) adult female, adult male, nymph, and larva.
Modified and reproduced from Centers for Disease Control and Prevention. Lyme Disease. Available at: https://www.cdc.gov/ticks/life_cycle_and_hosts.html. Accessed January 25, 2017.
Figure 05.F18: Incidence* of reported cases of Lyme disease by county—the United States, 2014. *Per 100,000 population
Modified and reproduced from Centers for Disease Control and Prevention. Summary of notifiable diseases—the United States, 2014. MMWR. 2016;63(54):117.
Figure 05.F27: How Zika spreads
Figure 05.F28: Scanning electron microscopic image of Ebola virus particles
Figure 05.F19: West Nile Virus transmission cycle.
Figure 05.F20: West Nile virus. Incidence* of reported cases of the neuroinvasive disease—the United States and U.S. territories, 2014. *Per 100,000 population
Figure 5.22 This is a deer mouse, Peromyscus maniculatus, a hantavirus carrier that becomes a threat when it enters human habitation in rural and suburban areas.
•The main host for the hantavirus is the deer mouse—Peromyscus maniculatus, found throughout North America.
Figure 05.F23: Three CDC health officials inspecting specimens suspected of being connected with a hantavirus outbreak.
Figure 05.F24: Hantavirus pulmonary syndrome (HPS) cases,* by state of residence: 1993—January 8, 2017. *N = 659 in 31 states
Figure 05.F25: World distribution of dengue—2008.
Figure 05.F26: A female Aedes aegypti mosquito, which is the primary vector for the spread of dengue fever.
Figure 05.F31: Timeline of course for a patient with presumptive abortive human rabies—Texas, 2009.
Figure 05.F32: Distribution of major rabies virus variants among mesocarnivores* in the United States and Puerto Rico, 2008 to 2014. *An animal that consumes meat as 50% to 70% of its diet. Black diagonal lines: fox rabies variants (Arizona gray fox and Texas gray fox). Solid borders: 5-year rabies virus variant aggregates for 2009 through 2014. Dashed borders: the previous 5-year aggregates for 2008 through 2013.
Figure 05.F33: Cases of rabies among wildlife in the United States, by year and species, 1983 to 2014 (in thousands).
Figure 05.F34: Spores from the Sterne strain of Bacillus anthracis bacteria
Figure 05.F35_1: Sentinel birds used to monitor for mosquito-borne viruses
Figure 05.F35_2: Sentinel birds used to monitor for mosquito-borne viruses.
