Name: how pathogens move between hosts
Uploaded: 2026-05-20T13:47:38.651Z
Duration: 1 min 24 s
Channel: JoVE

Pathogens spread from a reservoir, such as an infected individual, to susceptible hosts through three main routes: contact transmission, vehicle transmission, and vector transmission.Direct contact transmission, such as a handshake, can spread pathogens like Streptococcus pyogenes.Indirect transmission happens through contaminated objects or surfaces, called fomites.Droplet transmission happens when infected respiratory droplets are expelled during coughing or sneezing, spreading infection over short distances.Airborne vehicle transmission involves smaller droplets that remain suspended in the air, spreading pathogens over long distances without close contact.Pathogens can also spread via waterborne vehicle transmission, where consuming contaminated water causes illnesses like cholera.In mechanical vector transmission, a vector, such as a fly, passively carries pathogens on its body and transfers them to a host.In biological vector transmission, the pathogen multiplies within the vector. For example, Plasmodium develops inside mosquitoes before being transmitted to humans.

transmission of pathogens

Transmission of Pathogens

Pathogens spread from their reservoirs to susceptible hosts through three main routes: contact transmission, vehicle transmission, and vector transmission. Each route involves distinct mechanisms of transfer.Contact TransmissionThis category includes direct contact, indirect contact, and droplet transmission:<ul><li>Direct contact involves immediate physical interaction between individuals&#x2014;such as a handshake&#x2014;which can spread pathogens like Streptococcus pyogenes, the bacterium responsible for pharyngitis and skin infections.</li><li>Indirect contact occurs when a host touches a contaminated surface or object, known as a fomite. Examples include shared medical instruments, which can transmit pathogens like SARS-CoV-2.</li><li>Droplet transmission happens when respiratory droplets produced during coughing or sneezing travel short distances&#x2014;typically up to 1-2 meters&#x2014;and transmit pathogens causing infections such as pneumonia.</li></ul>Vehicle TransmissionVehicle transmission refers to the spread of pathogens via inanimate media, such as air, water, or food.<ul><li>Airborne transmission occurs when pathogens are carried in aerosolized droplets or dust particles smaller than 5 micrometers. These particles can remain suspended in the air and be inhaled. Mycobacterium tuberculosis, which causes tuberculosis, is transmitted in this manner.</li><li>Waterborne transmission results from ingesting contaminated water containing pathogens such as Vibrio cholerae, the bacterium responsible for cholera.</li><li>Foodborne transmission, another form of vehicle transmission, involves consuming contaminated food. This route is associated with diseases like salmonellosis, caused by Salmonella species.</li></ul>Vector TransmissionVector transmission involves living organisms that carry and transmit pathogens to humans.<ul><li>Mechanical transmission occurs when vectors&#x2014;such as houseflies&#x2014;passively carry microbes from contaminated sources like feces to food, without the pathogen undergoing development within the vector.</li><li>Biological transmission involves the replication or development of a pathogen inside the vector before transmission to a host. For example, Anopheles mosquitoes transmit Plasmodium species, the parasites responsible for malaria, after the pathogen completes part of its life cycle within the mosquito.</li></ul>In addition to the primary routes, pathogens can also spread through other important mechanisms:Vertical transmission occurs from mother to child during pregnancy, childbirth, or breastfeeding. Pathogens such as HIV and Treponema pallidum can be transmitted this way.Zoonotic transmission involves the transfer of pathogens from animals to humans, either through direct contact or via vectors. Examples include rabies virus and Leptospira species.Parenteral transmission refers to the introduction of pathogens directly into the body through breaches in the skin or mucosa, such as contaminated needles, blood transfusions, or organ transplantation. This route is associated with infections like hepatitis B, hepatitis C, and HIV.

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Education

JoVE Core

Microbiology

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Clinical Microbiology

KEY TERMS AND CONCEPTS

how pathogens move between hosts

Pathogens move from reservoirs to susceptible hosts through several routes of transmission. The main routes are contact transmission, vehicle transmission, and vector transmission. Each route uses a different path to spread infection.

Contact transmission includes direct contact, indirect contact, and droplet transmission. Direct contact happens through immediate physical interaction, such as a handshake, and can spread Streptococcus pyogenes, which causes pharyngitis and skin infections. Indirect contact happens when a person touches a contaminated surface or object called a fomite. Shared medical instruments can spread pathogens such as SARS-CoV-2 this way. Droplet transmission happens when coughing or sneezing releases respiratory droplets that travel short distances, usually 1 to 2 meters, and can cause infections such as pneumonia.

Vehicle transmission spreads pathogens through inanimate media such as air, water, or food. Airborne transmission happens when aerosolized droplets or dust particles smaller than 5 micrometers stay suspended in the air and are inhaled. Mycobacterium tuberculosis, the bacterium that causes tuberculosis, spreads in this way. Waterborne transmission happens when contaminated water is swallowed. A key example is Vibrio cholerae, which causes cholera. Foodborne transmission happens when contaminated food is eaten. Salmonellosis, caused by Salmonella species, is linked to this route.

Vector transmission involves living organisms that carry pathogens to humans. In mechanical transmission, vectors such as houseflies passively move microbes from contaminated sources like feces to food. The pathogen does not develop inside the vector. In biological transmission, the pathogen replicates or develops inside the vector before reaching a host. Anopheles mosquitoes transmit Plasmodium species, which cause malaria, after part of the parasite life cycle occurs in the mosquito.

Pathogens can also spread through vertical transmission, zoonotic transmission, and parenteral transmission. Vertical transmission passes from mother to child during pregnancy, childbirth, or breastfeeding, and it can involve HIV and Treponema pallidum. Zoonotic transmission moves from animals to humans through direct contact or vectors, as seen with rabies virus and Leptospira species. Parenteral transmission enters the body through breaks in the skin or mucosa, such as contaminated needles, blood transfusions, or organ transplantation, and it is associated with hepatitis B, hepatitis C, and HIV.

How Pathogens Move Between Hosts

infectious diseases and their occurrence

How Infectious Diseases Spread in Populations

Infectious diseases spread in populations in several recognizable patterns. These patterns depend on the pathogen, population immunity, environmental conditions, and social behavior. Public health teams use these patterns to guide surveillance and intervention. Sporadic disease appears only now and then. It occurs irregularly and infrequently, with no predictable pattern in time or place. These cases are usually isolated and do not show sustained transmission in a population. An outbreak is a...

reservoir of infection

How Pathogens Persist and Spread

Pathogens spread through reservoirs of infection. A reservoir is the natural place where a pathogen lives, grows, and multiplies. It acts as a constant source of infection. Reservoirs can be living or nonliving, and that difference affects how diseases move through populations and how public health teams control them. Humans can serve as reservoirs for many viruses, bacteria, and parasites. Sick people may spread infection through direct contact, respiratory droplets, or contaminated objects.

Pathogens move from reservoirs to susceptible hosts through several routes of transmission. The main routes are contact transmission, vehicle transmission, and vector transmission. Each route uses a different path to spread infection. Contact transmission includes direct contact, indirect contact, and droplet transmission. Direct contact happens through immediate physical interaction, such as a handshake, and can spread Streptococcus pyogenes, which causes pharyngitis and skin infections.

colonisation of pathogens

How Pathogens Attach and Hide

Pathogens attach to host tissues, invade cells, and use evasion tactics to cause infection. Bacteria, fungi, viruses, and protozoa can all use these strategies to establish disease in the body. These steps help them persist in host environments and resist immune defenses and antimicrobial treatment. In bacteria, colonization often begins on epithelial surfaces such as the respiratory or gastrointestinal tract. Many bacteria use pili, also called fimbriae, to bind to specific receptors on host...

bacterial toxins

How Bacterial Toxins Harm Cells

Bacterial toxins harm host cells by helping pathogenic bacteria invade tissues and damage them. These virulence factors are broadly grouped into exotoxins and endotoxins. Exotoxins are protein toxins that bacteria secrete into the environment. Endotoxins are lipopolysaccharides, or LPS, that make up part of the bacterial outer membrane and are mainly released when cells break apart or shed membrane. Exotoxins usually act in a targeted way. They bind specific molecules on host cells, such as...

determinants of bacterial pathogenicity and virulence

determinants-of-bacterial-pathogenicity-and-virulence

How Bacterial Enzymes Spread Infection

Bacterial enzymes can help pathogens spread through the body and avoid immune defenses. These extracellular enzymes act as virulence factors, which are traits that increase a bacterium’s ability to cause disease. They support colonization, tissue invasion, and immune evasion. Some bacteria make enzymes that break down the host’s extracellular matrix, the material that helps hold tissues together. Streptococcus pyogenes secretes hyaluronidase, which hydrolyzes hyaluronic acid in connective...

regulation of bacterial virulence

Bacterial Virulence and the BvgAS Switch

Pathogenic bacteria control virulence gene expression by sensing environmental and host signals. This regulation helps them turn virulence factors on only when conditions favor infection and survival. It also helps them adjust to changing pressures during the infection process. Several regulatory strategies are used in bacteria. Two-component systems use a membrane sensor kinase and a cytoplasmic response regulator to pass along signals by phosphorylation. Quorum sensing lets bacteria detect...

investigation of disease outbreaks

Tracking Foodborne Outbreak Sources

Tracking foodborne outbreak sources is a key part of public health response. Multistate foodborne outbreaks can affect many people and require careful investigation to find the source and stop more illness. The Centers for Disease Control and Prevention (CDC) uses a seven-step process that combines lab results, interviews, and environmental checks. Outbreak detection often starts with PulseNet, the CDC’s national lab network. PulseNet uses whole genome sequencing, or WGS, to compare bacterial...

rapid identification of pathogens

MALDI-TOF Spectra for Microbe ID

MALDI-TOF MS helps clinical labs identify microbes by reading the protein pattern of a sample. It is a fast alternative to older culture-based and biochemical tests, which can take much longer and delay the right antimicrobial treatment. The method can identify many organisms at the species level within minutes. The process begins with a colony or a small amount of biomass from a clinical isolate. The sample is mixed with a chemical matrix, usually α-cyano-4-hydroxycinnamic acid, which helps...

automated microbial diagnostics

Vitek 2 in Microbe ID and Antibiotic Tests

The Vitek 2 system automates microbial identification and antibiotic susceptibility testing in clinical microbiology. It helps labs identify pathogens quickly and produce standardized results that support patient care. For identification, a pure microbial colony is first turned into a standardized suspension. That suspension is placed into an ID card, which has many wells filled with specific biochemical substrates. Separate ID cards are used for Gram-negative bacteria, Gram-positive bacteria,...

vaccines

How Vaccines Train Immune Memory

Vaccines train the immune system to recognize infectious agents before a real infection starts. They do this by introducing antigens, which are substances the immune system sees as foreign. This triggers an adaptive immune response and helps the body build immunological memory. That memory allows a faster and stronger response if the pathogen appears again. Vaccines can be grouped by the type of antigen they deliver. Whole-pathogen vaccines use either live attenuated or inactivated organisms.

key terms and concepts

Learn how pathogens spread through contact, vehicles, and vectors, plus vertical, zoonotic, and parenteral transmission with clear examples for grades 9–12.

How Pathogens Move Between Hosts | JoVE K12

JoVE Core Microbiology provides an engaging introduction to the microbial world and its influence on health, industry, and the environment. This comprehensive collection covers key concepts such as microbial structure, metabolism, genetics, and ecology. It introduces essential laboratory techniques and microscopy methods through visually engaging animations. Corresponding scientist-in-action videos bridge classroom concepts with real-world research and applications.

microbiology

How Pathogens Move Between Hosts

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