Modes of transmission Flashcards
3rd epizootiological factor
modes of transmission
what is mode of transmission
ways of spreading the pathogenic microorganism from source of infection to a suitable portal of entry of the susceptible host
a successful mode of transmission
involves transmission of pathogenic microorganism in at least 1 minimum infective dose
why do we need to know modes of transmission
for the most effective prophylaxis
factors affecting possibility of transmission
the pathogen environmental tenacity
environmental conditions
minimum infective dose
time duration of spread of pathogenic microorganism from source to susceptible host
environmental tenacity
the resistance of microorganisms to environmental conditions
most important environmental conditions
temperature and exposure to UV light
minimum infective dose
the lowest amount of pathogenic microorganism sufficient to cause infection
3 main modes of transmission
direct contact
indirect contact - inanimate fomites or live intermediates
human activities
source of infection v mode of spread
source = in a certain place in one moment, where a large amount of microorganisms are located just before the outbreak in susceptible group of animals
spread = implies an action, which usually lasts and allows pathogenic microorganism transmission
transmission by direct contact
is spread of a pathogen by direct contact between a sick or a carrier animal as a source of infection and the suitable portal of entry of a susceptible host
types of direct contact
direct body contact
fecal-oral and droplet transmission
transplacental transmission
cohabitation
direct body contact
possible for almost all infectious diseases
very effective as spreading occurs instantaneously so environmental conditions down affect infectivity
prophylaxis = prevent contact between sick animals and susceptible
example of disease spread this way = rabies
fecal-oral and droplets
involves excretion of pathogen in to faeces that contaminates body of animal
contamination of anterior part of GI tract of susceptible animal can occur - profuse diarrhoea (example - Rotavirus)
also indirect contact
droplets = excretion of at least 1 infective dose in droplets that come directly to the portal of entry of susceptible host (example = TB, covid)
prophylaxis = separation of sick and healthy
transplacental transmission
intergenerational transmission so is vertical transmission
transmission from mother to offspring via milk is also direct contact
prophylaxis = immunoprophylaxis of female
transovarial transmission
in birds and arthropods vertical transmission to eggs
cohabitation
living together in close co existence
can be considered a consequence of human activity
prophylaxis = separation of animals and immunoprophylaxis
indirect contact in general
requires an intermediary that will allow a pathogen to remain infective, in at least 1 infectious dose, during transmission from diseased/carrier animal to suitable portal of entry of susceptible host
allows transmission over long distances
can occur through inanimate and live intermediaries
indirect contact with fomites
involves transmission of a pathogen by mechanical transport from source to portal of entry
efficiency of this spreading is influenced by tenacity and minimum infectious dose, environmental conditions and duration of transmission
indirect contact - water
running water most important due to expansion of space
running water = often not found in minimum infective dose
standing water = easier to have a larger amount of pathogen
when microorganism transmitted through water = hydric infections or waterborne diseases
water also indirect source - when water spreads spores over an area or rain washes spores away eg Anthrax
prophylaxis = give animals clean, fresh water and control disinfection of water
indirect contact - food
GI tract = portal of entry = alimentary infections
can be transmitted over long distances and time via food eg BSE
2 ways of transmission:
-food originates from infected animal
- food contaminated during preparation and feeding of animals
prophylaxis = supervisor and control of microbiological safety of foo and storage etc
indirect contact - soil
soil diseases - anthrax, tetanus, blackleg and malignant edema
soil is a passive vehicle of the causative agent of spores - soil to wound
prophylaxis = remediation of soil containing spores (anthrax)
clostridium tetani - injury prevention, immunoprophylaxis, hyperimmune sera
indirect contact - air
airborne transmission = spread of an infectious agent caused by the dissemination of droplet producing aerosols that remain infectious when diseased animal is no longer present
possible for pathogens that are resistant to environmental conditions
when pathogen remains infectious in dust eg hantavirus
risk increased indoors - air conditioning
favoured at lower temps and more frequent in winter
prophylaxis = ventilation and staying outside
indirect contact - object
most common fomites
animal care equipment, drinking and feeding equipment
main mode of transmission for - dermatophytosis, parvovirosis, equine rhinopneumonitis, foot and mouth
prophylaxis = dont share equipment between different animals
indirect contact - premises/spaces
contaminated premises = source
bringing susceptible animal to premises = MOT
prophylaxis = disinfection of surfaces and objects in all areas
in vet clinics, organise admission of patients so contagious diseases ones avoid crossing paths with other patients
indirect contact - means of transport, vehicles
when it isn’t disinfected after carrying a sick/carrier animal
foot and mouth is highly resistant and can be mechanically transmitted on tyres or vehicle surfaces
prophylaxis = disinfect horse boxes etc and have drive through disinfection
indirect contact with inanimate fomites
1 - water
2 - food
3 - soil
4- air
5 - objects
6 - spaces
7 - means of transport
indirect contact with live intermediaries
passive and mechanical transmission
vertebrate animals
arthropods
humans - iatrogenic spread
indirect contact - vertebrates
same species - when intermediate animal is resistant to infection due to previous illness or immunprophylaxis
different species - dog or cat can be contaminated with foot and mouth and spread it to susceptible ungulate host
wild animals
birds
prophylaxis = prevent entry of animals of other species in to farms with susceptible animals and prevent contact with animals for which we do not know epizootiological data
indirect contact - arthropods
= transmissible infectious diseases/vector borne diseases
biological transmission = transmission of a pathogenic microorganism that multiplies in the arthropod
mechanical transmission = pathogen transmitted from contaminated surface or hematophagous transmission (proboscis contaminated with blood from sick animal and then feed on a susceptible one and pathogen is transmitted)
prophylaxis = insect repellents, nets, keep indoors at night
indirect contact - humans
iatrogenic spread = through veterinary work
clothes etc can be contaminated with pathogen and then mechanically transmitted by contact
human activities - animal, animal product and by product trade
disease spread by trade of sick or carrier animals
possibility of disease to be spread over long distance and transcontinentally
human activities - intensive farming and animal shelters
direct and indirect contact with living or inanimate objects constant
shelters = animals of unknown health and immune status, from different age groups and geographical areas mixed daily.
human activities - migratory and extensive animal husbandry
eg sheep herd moving from one pasture to another
extensively farmed animals more exposed to wildlife, rodents and arthropods which can be reservoirs for infectious diseases
human activities - exhibitions, fairs and competitions
direct contact of lots of animals from different epizootiological units
transport reduces resistance and stress during shows etc help the spread
human activities - war and natural disasters
resources channelled elsewhere so animal health and disease control not a priority
also during economic crises
human actives and modes of transmission
- trade of animals and products etc
- intensive farming and shelters
- extensive farming
- exhibitions, fairs and comps
- wars and natural disasters
vogralink chain
virulence and infectious dose
source of infection
modes of transmission
portal of entry
host susceptibility
portal of entry definition
a site through which microorganisms enter the susceptible host
often enter though same route they exited the reservoir
portals of entry
epithelial surfaces to the environment
1. skin
2. mucous membranes
3. placenta
skin as a portal of entry
intact skin = cornfield cells (keratin) and other non specific defence mechanisms eg acidity of skin secretions
protects body but can be broken by trauma or inoculation (arthropods)
diseases = Rabies, Bluetongue, Tetanus, Lepto
mucous membrane examples
resp tract
alimentary tract
genital tract
conjunctiva
non specific defence mechanisms of mm
- sticky mucous
- stomach = HCl and protein digesting emzymes
- saliva and lacrimal fluids = bacteria destroying enzymes
- nasal hairs
- cilia
- acidity of the vagina
- acidity of urine
placenta as a portal of entry
vertical transmission from mother to foetus
diseases = BVD, equine herpes, Lepto
diseases with unknown portals of entry
Lumpy skin disease
maybe arthropod vector?
infected bulls can excrete virus in semen but transmission through semen is not possible
unknown if transmission can occur via fomites
can be infected experimentally by inoculation with material from cutaneous nodules or blood
