Zoonotic diseases or zoonoses are diseases that are transmitted from vertebrate animals to humans either directly or via an arthropod vector. They can be transmitted from wild animals, livestock, or domestic pets and can be caused by virtually any family of bacteria, many viruses, and eukaryotic parasites. Some of the better known zoonotic diseases include Lyme disease, Rocky Mountain Spotted fever, leptospirosis, tularemia, brucellosis, giardia, equine encephalitis including West Nile, and rabiesÉall transmitted from wild animals. Some people also consider influenza a zoonotic disease, although the role of animals in influenza is a little more complicated than in the case of, say, Lyme disease. Except for the few initial humans who get the flu virus from animals, everyone else gets the virus from fellow humans. Livestock can transmit, usually through food, Salmonella, Campylobacter, and E.coli as well as brucellosis and many other diseases, and domestic pets can transmit cat scratch disease, some fungal and parasitic diseases, and of course, rabies. Anthrax is also a zoonotic disease although these days we think of it more in terms of bioterrorism. Those most at risk include farmers, veterinarians, slaughterhouse workers and pet owners, although anyone who eats meat is, of course, also susceptible to food borne zoonoses. The origin or source of the disease is referred to as the reservoir, and the transmitting agent, the vector. A reservoir in the case of zoonotic diseases is the animal from which the disease comes and is usually an animal that is not susceptible to disease caused by the pathogen in question. In the case of Salmonella and E. coli, for instance, these are normal flora of the animals which transmit them. The vector is usually a biting arthropod (all insects are arthropods but not all arthropods are insects) such as a tick (arthropod) or flea (insect). The mechanism of vector transmission can be either mechanical during which the vector acts to simply breach the skin much like a flying or crawling pin, or biologic, where the organism in question must be able to multiply or undergo other change in the vector. Chapter 13, pp 399-429, of Infectious Diseases in 30 Days by F.S. Southwick (McGraw-Hill, 2003) discusses some of these diseases. After reading this, or the appropriate section in your microbiology text, you should be able to answer the following questions. The computer cases in this section cover many different zoonotic diseases and will give you a fairly complete understanding of them.
Question 1 - Single Best Answer
What has led to the increased incidence in Lyme Disease during the past three or so decades?
A) resistance of fleas to insecticides
B) new species of mosquitoes breeding in the US
C) increased populations of deer in urban areas
D) increased dog ownership
E) increased cave explorations
Question 2 - Single Best Answer
What must the encounter of tick and human be like to transmit Lyme disease?
A) the tick has to be swallowed
B) the tick only has to crawl on the person
C) the tick has to attach but not feed
D) the tick has to attach for about 24 hours and feed
E) the tick has to burrow under the skin and remain for the duration of the disease; removing the tick will stop the disease
Question 3 - Single Best Answer
What skin lesion is pathognomonic for Lyme disease?
A) erythema chronicum migrans (erythema migrans)
B) rash on the palms and soles
C) chickenpox-like rash
D) black eschar
E) an annular inflamed scaling patch with a raised margin
Question 4 - Single Best Answer
Besides Lyme disease, what diseases are caused by spirochetes?
A) Rocky Mountain Spotted Fever and Erlichiosis
B) Syphilis and leptospirosis
C) urethritis and non-gonococcal urethritis
D) measles and mumps
E) cat scratch disease and bacillary angiomatosis
Question 5 - Single Best Answer
How many stages are there to Lyme disease?
A) 1
B) 2
C) 3
D) 4
E) 5
Question 6 - Single Best Answer
What are the symptoms of Rocky Mountain Spotted fever?
A) fever
B) headache
C) petechial rash
D) abdominal pain
E) all of the above
Question 7 - Single Best Answer
What is the vector for typhus fever?
A) human louse
B) dog flea
C) deer tick
D) mosquito
E) fire ant
Question 8 - Single Best Answer
How is brucellosis transmitted to humans?
A) unpasteurized milk
B) contact with wild hogs or their carcasses
C) contact with goats or their carcasses
D) contact with cattle or their carcasses
E) all of the above
Question 9 - Single Best Answer
What zoonotic disease has been the most deadly throughout history?
A) plague
B) typhus
C) influenza
D) rabies
E) all of the above have killed millions of individuals