DISEASE E&E (Transmission 1) Flashcards
Taxonomic overview of pathogens and parasites
-viruses
-bacteria
Eukaryotes:
-protozoan
-fungi
-nematoda (roundworms)
-platyhelminthes (flatworms)
-arthropods
Helminths:
-nematoda
-platyhelminthes
Platyhelminthes:
-cestoda (tapeworms)
-trematoda (flukes)
Arthropods:
-mites
-ticks
-lice
-mosquitoes
-flies
Epidemiological models:
-distinguished between microparasites vs. microparasites
Microparasites:
-viruses, bacteria, protozoans
-acellular and unicellular
-small and replicate inside the host (numerous)
>don’t grow and develop
Macroparasites:
-multi-cellular
-helminths, arthropods
-grow and develop inside the host (don’t multiply)
*large and few
Microparasite models:
-modelled with SIR models
-model the dynamics by tracking NUMBER of susceptible, infected, and recovered HOSTS
-all infected individuals are the same (*percent of infected individuals is informative)
Probability of transmission (or recovery): microparasites
-does NOT depend on NUMBER of microparasites in host
Helminth worms: microparasitic models
-have different lifecycle stages: eggs, larvae, adults
-often aggregated in their hosts
Macroparasite models:
-must tack the developmental stages
*measure PARASITIC BURDEN
-percent of infected individuals is of limited value
Parasitic burden:
-the number of parasites per host
-influences transmission
Ex. host with 10 adult worms sheds more eggs than a host with 1 worm
Transmission: microparasite vs. macroparasite
-microparasite: direct, vector-borne
-macroparasite: direct, complex life cycles
Effect on host fitness: microparasite vs. macroparasite
-microparasite: mortality (IMMUNE system gets OVERWHELMED)
-macroparasite: morbidity
Steps in the parasite life-cycle:
- Finding a host
- Infection through the outer barrier and establishment in the host (Ex. skin)
- Growth or multiplication of the parasite inside the host
- Reproduction
- Development of transmission stages and transmission to the next host
Reproduction example:
-by exchange of genetic material between co-infecting strains
Lifecycle of rabies:
- Dog bit breaks the skin and dog saliva with virus contaminates the tissue
- Virus uses PNS as transport system to enter the CNS including the brain=preferred tissues
- Infection of CNS causes changes in behaviour that enhance virus transmission
- Rabies virus contaminates salivary glands
Rabies infection of CNS behaviour change:
-increased aggression and biting
Rabies contaminates salivary glands:
-so that the infected host will transmit the virus to a naïve host following a bite
Pathogen lifecycle determines:
-mode of transmission
-tissue tropism
-pathology
-disease symptoms
Respiratory pathogens:
-colonize the mucous membranes of the respiratory system
-cause symptoms like mucous production and coughing that facilitate pathogen transmission
GI pathogens:
-colonize the mucous membranes of the GI tract
-cause symptoms like diarrhea that facilitate pathogen transmission
Vector borne pathogens (VBPs):
-colonize the circulatory system to facilitate acquisition by blood-feeding arthropod vectors
Transmission definition:
-process where a pathogen/parasite transits from an infected host to an uninfected host
-different pathogens/parasites are transmitted in different ways
Mode of transmission is a critical factor for
-understanding biology of an infectious disease
-control of infectious diseases
Types of transmission:
-horizontal
-vertical
*in most vertebrate pathogens: HT is more important than V
Vertical transmission:
-mother transmits pathogen to her offspring
-vertebrate pathogens with VT also have HT
>pathogens with only VT are rare
Horizontal transmission:
-pathogen transmission between unrelated individuals
-can occur between individuals of same or different generations
Salmonella in chickens:
-causes GI disease in many vertebrate species
-colonize GI tract and cause diarrhea
-HT occurs via fecal-oral route
-persist in environment form long periods of time (weeks to years)
VT of Salmonella Enteritidis and food poisoning:
-colonizes ovaries and oviduct of the chicken reproductive tract
-yolk, albumen (egg white) and eggshell can all be contaminated
-VT: infected hens lays infected eggs that produce infected chicks=produce infected eggs
>humans get food poisoning when they consume contaminated eggs
Pestiviruses in livestock examples:
-bovine viral diarrhea (BVDV) in cattle
-classical swine fever in pigs
-Border disease in sheep
Pestiviruses in livestock:
-shed in fecal material, urine, and nasal secretions (HT)
-immunocompetent animals infected via direct transmission clear the infection
-viruses commonly cross the placenta and infect the fetus (VT)
Outcome of pestviruses VT:
-abortion
-persistently infected offspring that are super spreaders
BVDV:
-infection of dam during gestation causes immunotolerance and birth persistently infected (PI) calves
>PI don’t have a competent immune system at the time of infection
>viral cells were accepted as self during immune system development
PI individuals:
-shed high numbers of virus over their lifetime=highly effective horizontal transmission
Horizontal transmission types:
- Direct
-Close contact
-Contaminative (distant) - Indirect
-Arthropod vector
-Intermediate host
-*anytime when multiple species are involved
Close contact:
-skin-skin
-sexual
-aerosol
-secretions/excretions
-carcasses
Contaminative (distant):
-air-borne
-water-borne
-soil-borne
-fomites
Skin to skin: ex. cattle ringworm
-fungal skin disease
-causative agent: cattle ringworm fungus
-skin-to-skin contact between sick and healthy animals
Cattle ringworm: symptoms
-patches of hair loss
-desquamation
-formation of thick crusts
Cattle ringworm: economics
-spoils milk
-meat
-leather quality
Sexual transmission: brucellosis in dogs
-affects many animals including dogs, cattle, swine and goats
-causative agent: brucella canis
-infected dogs have bacteria in their genital secretions
-oral and sexual transmission
-reproductive problems and other symptoms
Biting: FIV in cats
Biting: FIV in cats
-feline immunodeficiency virus
-affects cats world wide
-causes AID-like syndrome but not typically fatal
-compromises the immune system of cats by infecting WBC
FIV transmitted:
-mostly through deep wounds
>only a problem if the cats fight
-low risk of transmission via sharing water bowls, food bowls and litter box
*males more likely to be infected than males
Pathogens can be spread through:
-air
-soil
-water
Foot-and-mouth disease (FMD):
-example of direct airborne transmission
-highly infectious viral disease
-causation: FMD virus (picornavirus)
-affects ungulates, humans are rarely infected
-affects young animals more
FMD hosts:
-cattle
-water buffalo
-sheep
-goats
-pigs
-antelope
-deer
-bison
FMD symptoms:
-blisters inside mouth, foamy salvia and drooling
-blisters on feet that can rupture and cause lameness
FMD transmission:
-close-contact animal-to-animal spread
-fomites (inanimate objects)
-food (eg. Dried hay)
-motor vehicles
-long-distance aerosol spread
Optimal conditions for long-range air-borne transmission of FMDV:
- High virus emission: pigs in acute state sheds lots of virus
- Low dispersal rate: gentle winds and a stable atmosphere
- High virus survival: relative humidity (more than 55%)
*RESULTS IN: large numbers of susceptible livestock exposed to virus plume for many hours
*cattle have low infectivity threshold
Giardiasis: direct waterborne transmission
-caused by protozoan parasite: Giardia duodenalis
-hosts: humans, beavers, cows, rodents and sheep
-common parasitic disease of humans around the world
Giardiasis infection occurs by:
-ingestion of contaminated food or water
-animal-to-animal contact
*cysts can survive for 3 months in cold water
Giardiasis symptoms:
-diarrhea: facilitates transmission
Anthrax: direct soilborne transmission:
-causes severe illness in both humans and animals
-cause: Gram-positive bacterium (Bacillus anthracis)
-found in soil
-affects domestic and wild animals world-wide
-endemic in Latin America, parts of Africa and Asia
-rare in North America
Anthrax North America:
-people can get sick if they contact infected animals or contaminated animal products
Where anthrax is endemic:
-bacterium infects grass-eating animals, which encounters spores in the environment as they graze
Anthrax spores:
-can persist in environment for a long time (decades)
-infection happens when animals breath in or ingest spores in soil, plants, or water
-activated when ingested and turn into active growing cells
Active anthrax:
-bacteria multiply inside host and disseminate using circulatory system
-bacteria produce endotoxins that cause severe illness in host and ultimately death
*carcass contains millions of spores that contaminate the soil for the next victim
Gruinard Island and anthrax:
-UK studied anthrax as a bioweapon
-exploded bombs with anthrax on an island
-all 80 test sheep died within days of exposure
-decontaminated the island
>tons of formaldehyde
>removed topsoil
-test sheep remained healthy
-humans could go back on (48 years later)
