Micro chapter 31
a. Rabies i. The major enzootic reservoirs of rabies virus in the US are raccoons, skunks, coyotes, foxes, and bats ii. The virus enters the body from virus contaminated saliva through a wound bite or through contamination of mucous membranes b. Lyme disease i. Caused by infection with a spirochete, Borrelia burgdorferi, transmitted by a tick bite ii. The ticks that carry B. Burgdorferi feed on the blood of birds, domesticated animals, various wild animals, and humans iii. Cells of B. burgdorferi are transmitted to humans while the tick is obtaining a blood meal c. Yellow fever i. Several arthropod transmitted diseases are caused by flavivirus 1. These are single stranded plus sense RNA viruses transmitted by the bite of an infected arthropod 2. Because of this characteristic mode of transmission, these viruses are also called arboviruses d. West nile i. Transferred to hosts by the bite of an infected mosquito ii. Infected birds develop a systemic viral infection that is often fatal so mosquitos feeding on viremic birds are infected and can then infect other susceptible birds, renewing the cycle e. Anthrax i. B. anthracis lives a saprophytic existence in soils, growing as an aerobic chemoorganotroph and forming endospores when they conditions warrant ii. From soil, cells or spores of B. anthracis can become embedded in animal hair, hides, or other animal materials, or can be ingested, and from here the disease can develop allowing B. anthracis spores to be transmitted to humans iii. Anthrax is primarily seen in domesticated farm animals, particularly in cattle, sheep, and goats and is transmitted from them to humans. f. Plague i. Plague is transmitted by several species of fleas, a main one being Xenopsylla cheopis, the rat flea. ii. Fleas ingest Y. pestis cells in a blood meal and the bacterium multiplies in the flea's intestine iii. From there, the infected flea transmits the disease to rodents or humans in the next biteiv. The most common form of plague is the bubonic plague
Contrast the modes of transmission of the following diseases: rabies, Lyme disease, yellow fever, West Nile disease, anthrax, and plague. Which of these diseases could be virtually eliminated in humans by control of the disease vector and which could not and why?
Lyme disease
a tick transmitted disease caused by spirochete borrelia burgdoferi
Spotted Fever Rickettsiosis
a tick-transmitted disease caused by Rickettsia rickettsii, characterized by fever, headache, rash, and gastrointestinal symptoms; also called Rocky Mountain spotted fever
rabies
a usually fatal neurological disease caused by the rabies virus, which is usually transmitted by the bite or saliva of an infected animal
Zoonosis
an animal disease transmissible to humans
Hemorrhagic fever with renal syndrome (HFRS)
an emerging acute disease characterized by shock and kidney failure, caused by rodent hantavirus
Hantavirus Pulmonary Syndrome (HPS)
an emerging, acute disease characterized by pneumonia and caused by rodent hantavirus
Enzootic
an endemic disease present in an animal population
plague
an enzootic disease in rodents caused by Yersinia pestis that can be transferred to humans through the bite of a flea
epizootic
an epidemic disease present in an animal population
Gas Gangrene
tissue destruction due to the growth of proteolytic and gas-producing clostridia
headache, backache, chills, fatigue & rash
what are the primary symptoms of Lyme disease?
-as bacteria grow they produce enzymes that destroy collagen and tissue proteins and excrete series of toxins. -A-toxin: virulence factor in gangrene-> bc the general ability of the pathogen to grow rapidly in warm, moist, and protein rich environments
How does the physiology of C. perfringens make it suitable for growing in puncture wounds?
-vector: mosquito - reservoir: birds
Identify the vector and reservoir for the West Nile virus.
-yellow fever: Vector- mosquitos; reservoir- human and nonhuman primates - Dengue fever: Vector- mosquitos; reservoir- humans and mosquitos
Identify the vector and reservoir for yellow fever and dengue viruses.
in the NE and upper midwest-> areas where deer are abundant
In the United States, where is Lyme disease most prevalent?
- typhus: louse - spotted fever: dogs and wood ticks - ehrlichiosis: ticks of mammalian reservoirs including deer, rodents and humans
What are the arthropod vectors and animal hosts for typhus, spotted fever rickettsiosis and ehrlichiosis?
-vector: rat flea - reservoir: rodents or humans -treatment: treated with gentamycin or streptomycin
What are the insect vector, the natural host reservoir, and the treatment for plague?
- protein capsule: it prevents killing by macrophages - toxins it produces: leads to worsening of symptoms
What are the major virulence factors of Bacillus anthracis?
- cutaneous: bacterium usually remains localized on skin and treatable - GI: triggered by ingestion of spores (under cooked meat) - pulmonary: (most dangerous because it becomes systemic) inhalation of endospores
What are the three forms of anthrax, and which is most dangerous?
•Victim can be passively immunized with rabies immune globulin (purified human Abs to rabies virus). injected at site of bite and intramuscularly. They should also be actively immunized with virus vaccine
What is the procedure for treating a human bitten by an animal if the animal cannot be found?
- oral vaccines have reduced the incidence and spread of rabies in limited areas. if herd immunity could be established in some of the key carriers-> incidence would decrease dramatically. - The rabies problem is primarily with wild animals, where traditional means of vaccination are impossible. However, experimental trials with an oral rabies vaccine administered in food "baits" have reduced the incidence and spread of rabies in limited geographic areas.
What major advantage does an oral vaccine have over a parenteral (injected) vaccine for rabies control in wild animals?
avoiding host & using insect repellants & wearing tick proof clothing
What precautions can be taken to prevent rickettsial infections?
HPS strains are more prevalent in the americas-> these strains typically show a significantly higher mortality rate than HFRS strains
Why are hantaviruses considered a major public health problem in the United States?
it can cause brain abnormalities and other birth defects in infected zika mothers. it readily infects neural cells that form the cerebral cortex. it can also cause an autoimmune disease
Why is Zika virus disease considered dangerous even though it rarely kills?
tetanus
a disease characterized by rigid paralysis of the voluntary muscles, caused by an exotoxin produced by Clostridium tetani
typhus
a louse-transmitted disease caused by Rickettsia prowazekii, characterized by fever, headache, weakness, rash, and damage to the central nervous system and internal organs
west nile fever
a neurological disease caused by West Nile virus, a virus transmitted by mosquitoes from birds to humans
- Infection: Cells of C. tetani normally gain access to the body through a soil-contaminated wound, typically a deep puncture. In the wound, anoxic conditions develop around the dead tissue and allow germination of endospores, growth of the organism, and production of a potent exotoxin, the tetanus toxin (also called tetanospasmin). C. tetani is essentially noninvasive; its sole ability to cause disease is through toxemia, and thus tetanus is observed only as the result of untreated deep tissue injuries. - Effects: The toxin directly affects the release of inhibitory signaling molecules in the nervous system. These inhibitory signals control the "relaxation" phase of muscle contraction. The absence of inhibitory signaling molecules results in rigid paralysis of the voluntary muscles, often called lockjaw because it is observed first in the muscles of the jaw and face. Preceding actual lockjaw, tetanus symptoms typically include mild spasms of facial muscles and muscles of the neck and upper back. Later on, the paralysis extends to the torso and lower body - Differs: C. perfringens alpha toxin, which is distinct from the toxins the bacterium produces in perfringens food poisoning, is a major virulence factor in gangrene, as is the general ability of the pathogens to grow rapidly in the warm, moist, and protein-rich environment created by an invasive injury. Alpha toxin is a phospholipase that hydrolyzes the membrane phospholipids of host cells, leading to cell lysis and the typical accumulation of gas and fluids that accompanies gas gangrene
Describe infection by Clostridium tetani and the effects of tetanus toxin. How does the mode of action of tetanus toxin differ from that of alpha toxin produced by C. perfringens?
- If a domestic animal, generally a dog, cat, or ferret, bites a human, especially if the bite is unprovoked, the animal should be held in quarantine for 10 days to check for signs of rabies. - If the animal exhibits rabies symptoms, or a definitive diagnosis of its illness cannot be made after 10 days, the human should be passively immunized with rabies immune globulin (purified human antibodies to rabies virus) injected at both the site of the bite and intramuscularly. The patient should also be actively immunized with a rabies virus vaccine. Because of the very slow progression of rabies in humans, this combination of passive and active immune therapy is nearly 100% effective, stopping the onset of the disease.
Describe the sequence of steps you would take if your child received a bite (provoked or unprovoked) from a stray dog with no collar and record of rabies immunization. Present one scenario in which you were able to capture and detain the dog and another for a dog that escaped. How would these procedures differ from a situation in which the child was bitten by a dog that had a collar and rabies tag with documented, up-to-date rabies immunizations?
- Hantaviruses infect rodents w/o causing disease-> virus goes to human by inhalation of virus contaminated rodent excreta (urine)-> humans become accidental host - avoiding contact with rodents, destruction of mouse habitat, restriction of food supplies and aggressive rodent extermination
Describe the spread of hantaviruses to humans. What are some effective measures for preventing infection by hantaviruses?
- administer medical care to wounds, clean/thoroughly remove damaged tissue, revaccination, administration of antitoxin preparation
Describe the steps necessary to prevent tetanus in an individual who has sustained a puncture wound.
- Control of WNV illness is much the same as for other vectorborne diseases: Limit exposure to mosquitoes using insect repellents containing DEET or wear tight-fitting clothing. Spraying for mosquitoes has limited effectiveness, but removal of mosquito breeding grounds, particularly sources of standing water, is very helpful in controlling mosquito populations. A veterinary WNV vaccine is widely used in horses where the mortality risk demands it, but no human WNV vaccine is currently available. - costs: at community level- $20,000-$59,000; individual level: couple hundred a month - yes we have a mosquito abatement program in Lafayette - methods: mosquito spraying trucks - cover garbage cans, maintain the pools, eliminate standing water.
Devise a plan to prevent the spread of West Nile virus to humans in your community. Identify the relative costs involved in such a plan, both at the individual level and at the community level. Find out if a mosquito abatement program is active in your community. What methods, if any, are used in your area for the reduction of mosquito populations? What is a simple way to limit mosquito numbers around your residence?
-sylvatic: is enzootic, among rodents -bubonic: most common; buboes develop on infected individuals - systemic: the rapid spread of y. pestis throughout the body - pneumonic: occurs when Y. Pestis reaches the lungs
Distinguish among sylvatic, bubonic, septicemic and pneumonic plague.
- avoiding contact with the vector, insect repellants containing DEET, wearing snug-fitting clothing and a thorough body exam following walks in tick infested environments
Outline methods for prevention of Borrelia burgdorferi infections.
rickettsias
obligate intracellular bacteria of the genus Rickettsia and related genera responsible for diseases including typhus, spotted fever rickettsiosis, and ehrlichiosis
