Presentation on theme: "Fleas & Plague Announcements Should have Chap 9 read by today Presentation today by Jonathan Rogers On Deck for Thursday Philip Crain, Gordon Chaney. Subject."— Presentation transcript:
Fleas & Plague Announcements Should have Chap 9 read by today Presentation today by Jonathan Rogers On Deck for Thursday Philip Crain, Gordon Chaney. Subject will be: Black flies, sand flies, biting midges and their diseases Read Chaps 10, 11, 12, 13 Will review for hour exam on Thursday Note “In the News” on the website
Quiz Review Question 1 – B, A, D. Note: Because of typo: E,A, D also was acceptable. Grading – 2 out of 3 = full credit, 1 right = 1 point. Question 2. Grading – 4/5 = full credit, 2 or 3/5 = 1 point X Allergies X Psychological Stress __ Trench Fever & Relapsing Fever X Intermediate Hosts of Animal Parasites __ or X Food Contamination Question 3. Grading – 4/5 = full credit, 2 or 3/5 = 1 point. __ or X Lice are solenophages __ Bed bugs are laterally flattened X All bugs are adapted to feeding on liquids X Bed bugs are in the same order as Kissing Bugs __ Bed bugs are actually more closely related to lice than to Conenose bugs
Quiz Review Question 4. Best Answer in Class “It is indirectly transmitted through the feces of the bug when the host scratches it into the biting wound or site or into mucus [sic] membranes.”
Class Quiz Scores
Disease pathology Pathogen replicates mainly within vascular endothelial cells. Infected cells proliferate and degenerate, results in vascular occlusion. Occlusion induces a focal ulcer followed by hematogenous dissemination of the pathogen systemically. Abrupt onset of clinical disease after ~4 weeks: headache, fever, and often a hemorrhagic rash. Ocular lesions sometimes occur as with all of the diseases produced by Rickettsiae.
Louse-borne Relapsing Fever Spirochete bacterium, Borrelia recurrentis Pathogen infects the louse blood stream, is transmitted when the louse is crushed & rubbed in to the skin. Few thousand/year, 95% of cases are in Ethiopia.
Trench Fever Bacterial disease, Bartonella quintana A form of “Bartonellosis”. We’ll see another one later. Like typhus, transmitted in louse feces. Often asymptomatic in healthy hosts. May express nonspecifically in stressed hosts. Increased association of stress & urban environments leads to term: “Urban Trench Fever”.
Fleas Order Siphonaptera with 15 families & about 2,500 spp. All spp. are ectoparasites of vertebrates, almost all (94%) target mammals. Closest living relatives are the Boreidae (snow scorpionflies) in the Order Mecoptera (scorpionflies) Boreid example
Flea Identification Identification is based on external morphology Usually difficult on “raw” specimens but easy on “cleared” specimens Several pictorial keys that are easy to use. Here is a good one from CDCHere Uncleared SpecimenCleared Specimen
Flea Identification: What is this flea?
Note the location of the ocular bristle
Flea Identification: What is this flea?
Medical/Public Health Significance Allergies Tungiasis – infestation by chigoe fleas Others (rickettsia, helminths, Q-fever, other pathogens). Murine (endemic) Typhus Plague: 3 forms –Bubonic is from the flea –Pneumonic from aerial dispersal –Septicemic from high-titer injection
Murine Typhus Also called “endemic typhus” or “flea-borne typhus”, see book for other names Rickettsial: Rickettsia typhii (different species than epidemic typhus, R. powazekii) Flea acquires pathogen from rats, passes it in feces, feces get scratched into skin. No obvious negative effect on flea (unlike R. powazekii which kills the louse). Patients present with mild – high fever, prostration, sometimes rash. Debilitation can be a couple of months, low fatality rate.
Plague Bacterial disease, Yersinia pestis Primarily a rodent pathogen, humans are accidental hosts When ingested, bacterium multiplies in flea gut, blocks it. Future attempts at feeding result in regurgitation of contaminated blood.
Manifestation Following injection into the new host, initial replication is inside tissue macrophages. Macrophages rupture, releasing larger numbers of bacteria into the blood stream. Many attack the draining lymph nodes, which become hot, swollen, tender, and hemorrhagic, giving rise to the characteristic black buboes responsible for the name of this disease. Within hours of the initial flea bite, the infection spills out into the bloodstream, leading to substantial involvement of the liver, spleen, and lungs. Patient develops a severe bacterial pneumonia, exhaling large numbers of viable organisms into the air during coughing fits representing a highly contagious health hazard to caregivers. Incubation period is 1 – 6 days (depending on form) and patient remains infectious for 3 weeks or death. Once infected/contaminated, most rodents & fleas remain infectious for life.
Spread of the Black Death
Historical Impact Example: The Horse Plague
Horse Plague Impact Spain ceased active colonization from Spain. Essentially froze Spanish influence. Italy never colonized the Americas French colonial aspirations were restricted in their infancy. In the absence of competition from Spain, Portugal, Italy, & France – England developed a blue-water navy.
Why the periodic pandemics? Three biotypes (“biovars”) of Y. pestis: –biovar ‘Antiqua’ – Justinian’s Plague (541) –biovar ‘Medievalis’ – Black Death (1347) –biovar ‘Orientalis’ – Chinese Plague (1894) At least some pandemics were more related to the vector than to the pathogen. –E.g. Horse Plague (1512) was probably driven by the human flea, Pulex irritans rather than the Oriental Rat Flea, Xenopsylla cheopis
Current Status of Plague Between 1998 and 2008, nearly 24,000 cases have been reported, including about 2,000 deaths In 2003, 9 countries reported 2118 cases and 182 deaths. 98.7% of those cases and 98.9% of those deaths were reported from Africa. Most serious current epidemic is in the Congo (FKA Zaire). August, 2009, outbreak in Qinghai, China
US Human Cases US normally has 10 – 20 cases/year