5.8: Modes of Transmission
- Page ID
- 116234
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)You know something about the modes of transmission from your own experience -- there are some communicable diseases you catch only through direct contact with another person, while others you can catch from germs left on a surface of a glass or plate.
What you might not be as familiar with are the differences among diseases that are airborne, vectorborne, or that rely on biological transmission routes.
Direct transmission refers to the immediate transfer of an infectious agent by direct contact between infected and susceptible individuals. For example, monkeeypox is usually passed through skin-to-skin contact. HIV/AIDS is another example of a disease that is usually passed through direct transmission. (The exception is when HIV is passed through infected blood in a needle, either in a medical setting or through sharing needles.)
Indirect transmission refers to communicable disease transmission involving an intermediate step. Here are some possible routes for indirect transmission:
- Vehicle borne transmission - an inanimate material or object that can serve as a source of infection. Many diseases can be transmitted in this way, but for some diseases, this is the main way they are spread -- for example dysentery or hepatitis A. One of the most notorious and immoral examples of this was when European colonial settlers gave blankets infected with smallpox to Native American communities, in order to intentionally kill off the Native Americans (genocide).
- Airborne transmission - dissemination of microbial aerosols to a suitable portal of entry. An aerosol is different from just droplets of spit that might be spread by a cough or sneeze. An aerosol is a suspension of dust and germs that can spread over a wide area and can stay in the air for a long time. Tuberculosis and influenza are examples of diseases transmitted in this way. Enclosed areas like shelters, crowded housing or nursing homes are prone to outbreaks of airborne diseases. Good ventilation helps disperse the aerosols and prevent the transmission of airborne diseases.
- Vectorborne transmission - transfer of disease by a living organism (vector). For example, mosquitoes spread malaria and dengue fever from one infected person to new hosts. While there are some diseases spread mechanically by vectors (for example, a fly could infect food by landing on it with its dirty feet), a bigger health challenge is biological transmission, where the infectious agent goes through some kind of change inside the vector. With biological transmission, the vector is necessary for the disease to be transmitted -- it can't happen any other way -- because the disease agent multiplies or develops in some way inside the vector before transmission occurs.
What's the difference between an animal vector of disease and an animal reservoir of disease?
- Diseases that have a biological vector use the animal (mosquito, tick, dog, whatever) to pick up the agent from one sick person, change it inside their body, then deposit it inside another person (host) to get them sick.
- An animal reservoir (like bats) might hold viruses or other microbe that can make people sick. Once the microbe passes from the animals to humans, though, if the disease continues to spread it is because humans can transmit it person-to-person without involving that animal.
