How can infectious diseases be controlled

Lifesaving medical treatments and procedures used in healthcare such as urinary catheters, tubes, and surgery increase the risk of infection by providing additional ways that germs can enter the body.

For example, healthcare provider hands become contaminated by touching germs present on medical equipment or high touch surfaces and then carry the germs on their hands and spread to a susceptible person when proper hand hygiene is not performed before touching the susceptible person.

Sprays and splashes occur when an infected person coughs or sneezes, creating droplets which carry germs short distances within approximately 6 feet. Close range inhalation occurs when a droplet containing germs is small enough to breathe in but not durable over distance. Inhalation occurs when germs are aerosolized in tiny particles that survive on air currents over great distances and time and reach a susceptible person.

Airborne transmission can occur when infected patients cough, talk, or sneeze germs into the air example: TB or measles , or when germs are aerosolized by medical equipment or by dust from a construction zone example: Nontuberculous mycobacteria or aspergillus.

Get Email Updates. To receive email updates about this page, enter your email address: Email Address. What's this? Links with this icon indicate that you are leaving the CDC website. An epidemic may reflect an escalation in the occurrence of an endemic disease or the appearance of a disease that did not previously exist in a population. The term outbreak is often used synonymously with epidemic but can occasionally refer to an epidemic occurring in a more limited geographical area; for example, a foodborne illness associated with a group gathering.

By contrast, a pandemic is an epidemic that has spread over a large geographic region, encompassing multiple countries or continents, or extending worldwide.

Influenza commonly occurs as a seasonal epidemic, but periodically it gives rise to a global pandemic, as was the case with H1N1 influenza.

Two fundamental measures of disease frequency are prevalence and incidence. Prevalence is an indicator of the number of existing cases in a population as it describes the proportion of individuals who have a particular disease, measured either at a given point in time point prevalence or during a specified time period period prevalence. In contrast, incidence a. In some circumstances, a secondary attack rate is calculated to quantify the spread of disease to susceptible exposed persons from an index case the case first introducing an agent into a setting in a circumscribed population, such as in a household or hospital.

It is defined as the average number of secondary cases generated by a single, infectious case in a completely susceptible population. Thus, a more accurate reflection of the potential for community disease spread is the effective reproductive number R which measures the average number of new infections due to a single infection. Herd immunity a. As a result of herd immunity, susceptible individuals who are not immune themselves are indirectly protected from infection Figure 4. Vaccine hesitancy, the choice of individuals or their caregivers to delay or decline vaccination, can lead to overall lower levels of herd immunity.

Outbreaks of measles in the United States, including a large measles outbreak at an amusement park in California, highlight the phenomena of vaccine refusal and associated increased risk for vaccine-preventable diseases among both nonvaccinated and fully vaccinated but not fully protected individuals Phadke et al. Herd immunity occurs when one is protected from infection by immunization occurring in the community.

Using influenza as an example, the top box shows a population with a few infected individuals shown in red and the rest healthy but unimmunized shown in blue ; influenza spreads easily through the population. The middle box depicts the same population but with a small number who are immunized shown in yellow ; those who are immunized do not become infected, but a large proportion of the population becomes infected. In the bottom box, a large proportion of the population is immunized; this prevents significant transmission, including to those who are unimmunized.

The proportion that needs to be immunized depends on the pathogen Table 3. Thus, Ro and R can be used to calculate the target immunization coverage needed for the success of vaccination programs. Proper diagnosis of infectious illnesses is essential for both appropriate treatment of patients and carrying out prevention and control surveillance activities. Two important properties that should be considered for any diagnostic test utilized are sensitivity and specificity. A test that is very sensitive is more likely to pick up individuals with the disease and possibly some without the disease ; a very sensitive test will have few false negatives.

Often, screening tests are highly sensitive to capture any possible cases , and confirmatory tests are more specific to rule out false-positive screening tests. Broadly, laboratory diagnosis of infectious diseases is based on tests that either directly identify an infectious agent or provide evidence that infection has occurred by documenting agent-specific immunity in the host Figure 5. Identification of an infecting agent involves either direct examination of host specimens e.

The main categories of analyses used in pathogen identification can be classified as phenotypic , revealing properties of the intact agent, nucleic acid-based , determining agent nucleic acid DNA or RNA characteristics and composition, and immunologic , detecting microbial antigen or evidence of immune response to an agent Figure 5.

Cultured material containing large quantities of agent can undergo analyses to determine characteristics, such as biochemical enzymatic activity enzymatic profile and antimicrobial sensitivity , and to perform phage typing , a technique which differentiates bacterial strains according to the infectivity of strain-specific bacterial viruses a. The ability of pathogen-specific PCR primers to generate an amplification product can confirm or rule out involvement of a specific pathogen. Sequencing of amplified DNA fragments can also assist with pathogen identification.

Most recently, next-generation sequencing technologies have made whole-genome sequencing a realistic subtyping method for use in foodborne outbreak investigation and surveillance Deng et al. The objective of immunologic analysis of specimens is to reveal evidence of an agent through detection of its antigenic components with agent-specific antibodies.

Serotyping refers to the grouping of variants of species of bacteria or viruses based on shared surface antigens that are identified using immunologic methodologies such as enzyme-linked immunosorbent assay ELISA and Western blotting. Methods of infectious disease diagnosis. Laboratory methods for infectious disease diagnosis focus on either analyzing host specimens or environmental samples for an agent upper section , or analyzing the host for evidence of immunity to an agent lower section. Closed solid bullets, category of test; open bullets, examples of tests.

Immunologic assays are also used to look for evidence that an agent-specific immune response has occurred in an exposed or potentially exposed individual. Serologic tests detect pathogen-specific B cell—secreted antibodies in serum or other body fluids. Some serologic assays simply detect the ability of host antibodies to bind to killed pathogen or components of pathogen e.

Others rely on the ability of antibodies to actually neutralize the activity of live microbes; as, for example, the plaque reduction neutralization test which determines the ability of serum antibodies to neutralize virus. Antibody titer measures the amount of a specific antibody present in serum or other fluid, expressed as the greatest dilution of serum that still gives a positive test in whatever assay is being employed.

Intradermal tests for identification of T cell—mediated immediate type Type I hypersensitivity or delayed type Type IV hypersensitivity responses to microbial antigen can be used to diagnose or support the diagnosis of some bacterial, fungal, and parasitic infections, such as, the Mantoux tuberculin test for TB. Based on the classic model of Leavell and Clark , infectious disease prevention activities can be categorized as primary, secondary, or tertiary.

Primary prevention occurs at the predisease phase and aims to protect populations, so that infection and disease never occur. For example, measles immunization campaigns aim to decrease susceptibility following exposure. The goal of secondary prevention is to halt the progress of an infection during its early, often asymptomatic stages so as to prevent disease development or limit its severity; steps important for not only improving the prognosis of individual cases but also preventing infectious agent transmission.

For example, interventions for secondary prevention of hepatitis C in injection drug user populations include early diagnosis and treatment by active surveillance and screening Miller and Dillon, Tertiary prevention focuses on diseased individuals with the objective of limiting impact through, for example, interventions that decrease disease progression, increase functionality, and maximize quality of life.

Broadly, public health efforts to control infectious diseases focus on primary and secondary prevention activities that reduce the potential for exposure to an infectious agent and increase host resistance to infection.

The objective of these activities can extend beyond disease control , as defined by the Dahlem Workshop on the Eradication of Infectious Diseases, to reach objectives of elimination and eradication Dowdle, ; Box 1. As noted earlier, the causation and spread of an infectious disease is determined by the interplay between agent, host, and environmental factors. For any infectious disease, this interplay requires a specific linked sequence of events termed the chain of infection or chain of transmission Figure 6.

The chain starts with the infectious agent residing and multiplying in some natural reservoir ; a human, animal, or part of the environment such as soil or water that supports the existence of the infectious agent in nature. The infectious agent leaves the reservoir via a portal of exit and, using some mode of transmission , moves to reach a portal of entry into a susceptible host. A thorough understanding of the chain of infection is crucial for the prevention and control of any infectious disease, as breaking a link anywhere along the chain will stop transmission of the infectious agent.

Often more than one intervention can be effective in controlling a disease, and the approach selected will depend on multiple factors such as economics and ease with which an intervention can be executed in a given setting. It is important to realize that the potential for rapid and far-reaching movement of infectious agents that has accompanied globalization means that coordination of intervention activities within and between nations is required for optimal prevention and control of certain diseases.

The chain of infection a. One way to visualize the transmission of an infectious agent though a population is through the interconnectedness of six elements linked in a chain. Public health control and prevention efforts focus on breaking one or more links of the chain in order to stop disease spread. The cause of any infectious disease is the infectious agent. As discussed earlier, many types of agents exist, and each can be characterized by its traits of infectivity, pathogenicity, and virulence.

A reservoir is often, but not always, the source from which the agent is transferred to a susceptible host. For example, bats are both the reservoir for Marburg virus and a source of infection for humans and bush animals including African gorillas.

However, because morbidity and mortality due to Marburg infection is significant among these bush animals, they cannot act as a reservoir to sustain the virus in nature they die too quickly , although they can act as a source to transmit Marburg to humans. Infectious agents can exist in more than one type of reservoir.

The number and types of reservoirs are important determinants of how easily an infectious disease can be prevented, controlled, and, in some cases, eliminated or eradicated. Animal, particularly wild animal, reservoirs, and environmental reservoirs in nature can be difficult to manage and, thus, can pose significant challenges to public health control efforts.

In contrast, infectious agents that only occur in human reservoirs are among those most easily targeted, as illustrated by the success of smallpox eradication. Humans are the reservoir for many common infectious diseases including STIs e. Humans also serve as a reservoir, although not always a primary reservoir, for many neglected tropical diseases NTDs as, for example, dracunculiasis a. Guinea worm. From a public health standpoint, an important feature of human reservoirs is that they might not show signs of illness and, thus, can potentially act as unrecognized carriers of disease within communities.

The classic example of a human reservoir is the cook Mary Mallon Typhoid Mary ; an asymptomatic chronic carrier of Salmonella enterica serovar Typhi who was linked to at least 53 cases of typhoid fever Soper, Animals are a reservoir for many human infectious diseases. Zoonosis is the term used to describe any infectious disease that is naturally transmissible from animals to humans. Zoonotic reservoirs and sources of human disease agents include both domestic companion and production animals e.

Control and prevention of zoonotic diseases requires the concerted efforts of professionals of multiple disciplines and is the basis for what has become known as the One Health approach Gibbs, This approach emphasizes the interconnectedness of human health, animal health, and the environment and recognizes the necessity of multidisciplinary collaboration in order to prevent and respond to public health threats.

Inanimate matter in the environment, such as soil and water, can also act as a reservoir of human infectious disease agents. The causative agents of tetanus and botulism Clostridium tetani and C. Legionella pneumophila , the etiologic agent of Legionnaires' disease, is part of the natural flora of freshwater rivers, streams, and other bodies. However, the pathogen particularly thrives in engineered aquatic reservoirs such as cooling towers, fountains, and central air conditioning systems, which provide conditions that promote bacterial multiplication and are frequently linked to outbreaks.

Soil and water are also sources of infection for several protozoa and helminth species which, when excreted by a human reservoir host, can often survive for weeks to months. Outbreaks of both cryptosporidiosis and giardiasis commonly occur during summer months as a result of contact with contaminated recreational water. Soil containing roundworm Ascaris lumbricoides eggs is an important source of soil-transmitted helminth infections in children.

Central to these interventions are surveillance activities that routinely identify disease agents within reservoirs. When humans are the reservoir, or source, of an infectious agent, early and rapid diagnosis and treatment are key to decreasing the duration of infection and risk of transmission. Both active surveillance and passive surveillance are used to detect infected cases and carriers. Some readily communicable diseases, such as Ebola, can require isolation of infected individuals to minimize the risk of transmission.

As part of the global effort to eradicate dracunculiasis, several endemic countries have established case containment centers to provide treatment and support to patients with emerging Guinea worms to keep them from contaminating water sources and, thereby, exposing others Hochberg et al. Contact tracing and quarantine are other activities employed in the control of infections originating from a human reservoir or source.

During the West Africa Ebola outbreak, key control efforts focused on the tracing and daily follow-up of healthy individuals who had come in contact with Ebola patients and were potentially infected with the virus Pandey et al. One Health emphasizes the importance of surveillance and monitoring for zoonotic pathogens in animal populations. For some diseases e. Once animal reservoirs and sources of infection are identified, approaches to prevention and control include reservoir elimination and prevention of reservoir infection.

The focus of prevention and control activities for these diseases reflects the extent to which a zoonotic pathogen has evolved to become established in human populations Wolfe et al. For some zoonotic diseases e. Currently, most human cases of avian influenza are the result of human infection from birds; human-to-human transmission is extremely rare.

Thus, reservoir elimination by culling infected poultry flocks is a recommended measure for controlling avian influenza in birds and preventing sporadic infection of humans CDC, Other zoonotic diseases demonstrate varying degrees of secondary human-to-human transmission following primary transmission a.

Both rates of spillover and the ability to sustain human-to-human transmission can vary widely between zoonoses and, in consequence, control strategies can also be quite different. For example, outbreaks of Ebola arise following an initial bush animal-to-human transmission event, and subsequent human-to-human transmission is often limited Feldmann and Geisbert, Thus, while Ebola outbreak prevention efforts would include limiting contact with bush animals, such efforts would not be useful for prevention of dengue outbreaks.

HIV is an example of a virus that emerged from an ancestral animal virus, simian immunodeficiency virus, but has evolved so that it is now HIV is an example of a virus that emerged from an ancestral animal virus, simian immunodeficiency virus, but has evolved so that it is now only transmitted human to human Faria et al.

Infectious agents exit human and animal reservoirs and sources via one of several routes which often reflect the primary location of disease; respiratory disease agents e. Other portals of exits include sites from which urine, blood, breast milk, and semen leave the host.

For some infectious diseases, infection can naturally occur as a result of contact with more than one type of bodily fluid, each of which uses a different portal of exit. While infection with the SARS virus most frequently occurred via contact with respiratory secretions, a large community outbreak was caused by the spread of virus in a plume of diarrhea Yu et al.

Control interventions targeting portals of exit and entry are discussed below. There are a variety of ways in which infectious agents move from a natural reservoir to a susceptible host, and several different classification schemes are used.

The scheme below categorizes transmission as direct transmission , if the infective form of the agent is transferred directly from a reservoir to an infected host, and indirect transmission , if transfer takes place via a live or inanimate intermediary Box 2.

Modes of Direct Transmission infective form of agent transferred directly from reservoir or host :. Modes of Indirect Transmission infective form of agent transferred indirectly from reservoir or infected host :.

Direct physical contact between the skin or mucosa of an infected person and that of a susceptible individual allows direct transfer of infectious agents. This is a mode of transmission for most STIs and many other infectious agents, such as bacterial and viral conjunctivitis a. Direct droplet transmission occurs after sneezing, coughing, or talking projects a spray of agent-containing droplets that are too large to remain airborne over large distances or for prolonged periods of time.

The infectious droplets traverse a space of generally less than 1 m to come in contact with the skin or mucosa of a susceptible host. Many febrile childhood diseases, including the common cold, are transferred this way. Infectious agents spread exclusively in this manner are often unable to survive for long periods outside of a host; direct transmission helps to ensure transfer of a large infective dose. Direct contact to an agent in the environment is a means of exposure to infectious agents maintained in environmental reservoirs.

In spite of the increased attention and all gained knowledge on EID, it may prove difficult to formulate policies on risk reduction. Part of this is due to lacking understanding of causality, trade-offs, and externalities of decisions. This paper aims to review existing literature on how human impacts are associated with disease emergence and transmission. The purpose of this analytic review is to provide a framework for evaluating the risks that anthropogenic ecosystem changes may have on disease transmission and dynamics.

Definitions of EID vary, including: a disease which incidence in humans has been increasing; a disease which has a tendency to spread geographically, cause an increased incidence, or infect a new species or new populations; or, a disease spreading within any host population 24 — Pathogens may also be considered emerging, for example, antimicrobial resistant bacteria.

These definitions can be similarly applied to wildlife and plant diseases 27 , 28 , in both terrestrial and marine ecosystems There can also be an apparent emergence of newly discovered or previously underdiagnosed diseases 24 , 26 , Taylor et al. Zoonotic pathogens were found twice as likely to be emerging as non-zoonotic, but this was only seen in some taxa bacteria and fungi.

The host jump occurring in zoonotic infection can either cause an establishment of the pathogen in the new population with subsequent spread, or there may be recurrent events of transmission from a reservoir to the new host, after which no further transmission occurs, or there is a limited small outbreak These often have a rapid intensification of agricultural systems, especially of livestock keeping, and increasing interactions between animals, humans, and ecosystems, often caused by rapidly changing habits and practices within societies 18 , Especially small-scale or backyard farmers may be disproportionally affected by the negative impacts of EID Emerging diseases, such as highly pathogenic avian influenza, can lead to industry decline or restructuring with negative effects on small-scale producers and value chain actors McMichael 38 proposed five categories of promoters for emerging infections: land use and environmental changes; demographic changes; host conditions; human consumption behaviour; and other behaviours such as social and cultural interaction, sexual habits, and drug use.

Apart from these, factors within the pathogen, such as the capacity to evolve through mutations, are important for disease emergence The EID that have received most publicity during the last decades have been viruses. RNA viruses are prone to emergence because of their rapid replication and high mutation rates, with around one misreading per replication, and large viral populations 40 , However, the increased evolutionary pressure of having to adapt to both invertebrate and vertebrate hosts creates a lower rate of mutation in vector-borne viruses, and most of their mutations are synonymous Apart from point mutations, viruses can evolve through recombination events, especially among segmented viruses.

The reassortment that occurs in influenza viruses is one example of this whereby influenza viruses create new combinations of genes. Single-stranded viruses may also recombine when different viral strains circulate in the same area, and occasionally infect the same cell, as in the example of Japanese encephalitis virus 43 , However, in spite of the increased tendency for recombinations among segmented viruses, single-stranded RNA viruses seem to be overrepresented among emerging pathogens Because of public health breakdown or complacency, many bacterial diseases have been re-emerging, such as cholera and plague in India One of the most alarming phenomena in bacteria is the spread of antibiotic resistance.

Although bacteria have a continuous evolution with mutations, they also have means of spreading their genetic material laterally between species through interchange of plasmids or integrons 46 — This capacity to share genetic material is not a phenomenon restricted to antibiotic resistance but an efficient way of handling different adverse environmental circumstances in nature as well 49 , In the same manner, lateral transfer may occur of virulence genes 48 , and integration of toxin gene elements from phages seems to commonly occur in Escherichia coli , although the toxins are not always expressed to the same amount Most studies seem to show that the acquisition of antimicrobial resistance genes in bacteria do cause a comparative disadvantage compared with non-resistant bacteria in the absence of antibiotics, but studies of some genes have shown no difference, or even the opposite.

A longer evolution together with a resistance gene may lower the costs for the bacteria Fungal infections are emerging not only among plants, where they have long been an important cause of losses, but also among fishes, corals, amphibians, bats, and humans In fact, fungal infections are contributing to the majority of extinction events that are known to have been caused by infectious diseases 52 , Many fungi further have the possibility to persist as free-living spores In addition to the fungi that directly infect humans and animals, fungi that produce toxins can cause disease indirectly.

Fumonisins and aflatoxins are toxins produced by different moulds, mainly Fusarium and Aspergillus species, and the growth of these fungi is promoted by climatic circumstances and bad storage conditions 54 , The toxins have severe health impacts on humans and animals, and the costs of diseases and of the condemned crops are high 56 , Climate changes are likely to affect the impact further Even though part of the increased reports of parasitic disease may be due to previous underreporting, the incidence does seem to be increasing.

Large parts of the industrialized countries have managed to reduce the burden of many parasites, whereas in many countries multiple chronic infections are common An emerging problem in parasites is increasing resistance, which cause many drugs to be ineffective In the analysis by Taylor et al.

There are, however, other infections of importance among animals. Chronic wasting disease in cervids is spreading in North America and affects cervid populations, but is believed to have low zoonotic potential New strains of atypical scrapie in sheep and the detection of other new transmissible spongiform encephalopathies have also caused increased concerns, both for emergence within animal populations as well as for their possible zoonotic implications Infections transmitted directly between individuals are dependent on the contact rate between susceptible and infectious people, and thus subsequently on the population density and the mixing of populations.

Direct transmission of zoonotic diseases requires contact between animal hosts and humans, as in the case of rabies transmission, but transmission can also occur in the other direction. Close contact increases risk of transmission from pets or livestock to their owners, and the growing demands for exotic pets 63 with subsequent increased trade further increases risk for introduction of new pathogens.

Food- and water-borne pathogens are the major contribution to the billions of annual diarrhoea cases that occur Increases in food-borne transmission may be an effect of the difficulties in handling the manure from animal production safely, as this can be a source of many zoonotic pathogens This is an issue both for small-scale farming where there may be no systems to handle manure at all, and in industrialized systems where the sheer amount of manure produced daily causes management problems.

In addition, increasing water scarcity and water pollution in the future 65 may cause increased risks for decreased food safety. Although arboviruses can be transmitted by a wide range of arthropods, mosquitoes are the most important from a veterinary and medical point of view and may have been parasitizing on mammalian blood for million years Disease from vector-borne pathogens often occurs as spillover events, as the pathogens generally circulate between reservoir hosts and the invertebrate vectors without causing apparent disease.

However, many vectors are not specific in their requirements of their feeding hosts and may feed on other animals. These opportunistic, oligophilic vectors can thus transfer a pathogen from a reservoir host to animals or humans where disease occurs. Often these new incidental hosts are less capable of amplifying the pathogen and are epidemiological dead ends. The complex nature of vector-borne transmission makes it difficult to predict how changes will affect the incidence.

Temperature affects both the longevity, the incubation period within the vector, abundance, behaviour, and the reproduction cycles of the mosquito and thus warmer climates may lead both to increased transmission as well as reduced, when the lifespan of the mosquito is reduced below the time required for the virus to replicate The essence is that any factors that contribute to shorter incubation periods, increased mosquito abundance, increased proportion of suitable hosts, or increased vector survival will increase the disease transmission.

The opportunistic behaviour of many vectors can cause them to change their feeding according to the host availability, and even mosquitoes with a strong preferences for humans will feed on other hosts if they are abundant enough Presence of multiple species can, in theory, have both a diluting effect, where the feeding on other species decreases the proportion of vectors feeding on the target species for a disease, and an amplifying effect where the access to multiple feeding hosts cause an increased abundance of vectors The dilution effect of other animals has been used in zooprophylaxis, when a species, often cattle, is used to divert mosquitoes away from another species, but this does not work if the vector abundance is increased The concept of Susceptible-Infected—Removed SIR has been used to model infectious diseases since it was proposed in the s.

The model is, however, simplified, and for more appropriate modelling it may be necessary to include a category of exposed and latently infected Generally, the spread of infectious diseases is promoted by all factors that increase the contact rate, especially between susceptible and infected individuals; create more susceptible individuals; and increase the time of infectiousness Actions causing the opposite will thus reduce the spread.

Often there are multiple steps before an action taken by humans converts into increased risk for disease, which may cause a delayed increase of incidence Fig. Because the disease dynamics of SIR is essential and basic to epidemiology of humans, animals, and plants, all factors proposed by the literature are listed here according to their effect on these categories. Thus, for the purpose of this framework, the factors: 1 increasing the number of susceptible individuals, 2 increasing the risks of exposure, and 3 increasing how infectious the infected individual is, are considered factors increasing the risks for disease emergence.

A new population can become at risk for an infection if a new pathogen is transferred to a previously uninfected area. This both can occur over a distance where a pathogen is brought by anthropogenic means, with an infected individual, in a vector, or in contaminated products, and it can be a slow progression into neighbouring areas, by animal, human, or vector movements; or through trade. Cultural exchange may also cause a population to adopt new habits and acquire new risks.

Furthermore, the number of susceptible individuals can be increased if the existing population in an area where a pathogen exists are increasingly immunosuppressed. This may occur in well-developed countries with increasing proportions of ageing citizens and increasing obesity-related diseases, and advanced medicine with subsequent iatrogenic immunosuppression; or in poorer nations where vaccination programmes cannot be supported and large parts are immunocompromised due to undernutrition or chronic infections It is also possible that a new species constitutes the new population at risk, if a pathogen makes a host jump.

The risk for a host jump is increased by all factors that force different species into contact with each other. The changes in land use and social drivers leading up to these changes may however be complex. The framework showing factors contributing to increased susceptible populations is shown in Fig. A major factor in the risk of exposure to a pathogen already in place is the pattern of interaction between individuals, which depends on the population density and behaviour.

Increasing urbanization, as well as intensified animal keeping, increases exposure. For vector-borne pathogens, the risk of exposure is dependent on the abundance of vectors, as well as the likelihood that these will feed on the appropriate host.

Because of the variety of vector habitats and the adaptability of vector species, it is difficult to exhaustively list all factors that may contribute to increases.

Pathogens causing infections through food and water are likely to be influenced by social factors, and by climate changes. A framework showing factors contributing to increased exposure is shown in Fig.

How infectious an individual is following an infection, and for how long time, is dependent on factors in the infected individual, on the pathogen, and the possibility in veterinary and medical care to cure the infection. A framework showing factors contributing to increased infectivity is shown in Fig. The manner in which anthropogenic activities affect the pathogen dynamics is not always evident and may have several steps. It is also necessary to remember that, because of the stochastic nature, the same scenario might not occur at two occasions, even though circumstances are apparently similar.

If a pathogen is dependent on a vector or a reservoir, the pattern may become more complex. Most changes done to existing ecosystems are done deliberately, often desired for economic or other reasons.

It must be remembered that many drivers of disease sometimes are associated with decreased spread of other diseases, or bring other benefits. In fact, many suggested drivers of disease are promoted by governments and society because of their clearly visible and desired positive effects on livelihoods and economies. Although globalization brings along opportunities for knowledge transfer, cultural and scientific exchanges, and rapid aid responses, the increasing globalization has also been suggested to be a reason for increased transfer of pathogens into new areas.

Historically, major transition periods when people travelled, and a mixing of populations were achieved, have been followed by large disease outbreaks and spread of pathogens This has been especially marked when travel is accompanied by large-scale societal dislocation as is the case for wars, and colonialization. In addition to human travels, millions of animals are transported annually, both legally and illegally, and only a minor portion is subject to disease control This may also affect wildlife, and trade with exotic and pet animals is most likely one of the causes behind the global spread of amphibian chytridiomycosis Moreover, pathogens do not necessarily need to be transported within a host but can also be transported in, for example, ballast water, in the example of cholera In summary, globalization has both desired and undesired effects.

On the other hand, it is essential for today's trade and economies and highly desired by the part of the world's population with economic means for travelling. Deforestation is often the result of the economically important logging industry; but it may also be a deliberate act to use a previously forested area for habitation, industry, or other purposes.

It often brings human inhabitants into the deforested area needing food, and bringing their livestock. Deforestation often creates more larval habitats, increasing the number of vectors All pregnant women should be tested and all babies should be vaccinated. Doctors recommend that your child get three doses of the Hepatitis B shot for best protection.

Typically, your child will need one dose at each of the following ages:. The Hepatitis A vaccine was developed in and since then has cut the number of cases dramatically in the United States. Hepatitis A is a contagious liver disease and is transmitted through person-to-person contact or through contaminated food and water. Vaccinating against hepatitis A is a good way to help your baby stay Hep A-free and healthy! Doctors recommend that your child get two doses of the hepatitis A vaccine.

Rubella is spread by coughing and sneezing. It is especially dangerous for a pregnant woman and her developing baby.

If an unvaccinated pregnant woman gets infected with rubella, she can have a miscarriage or her baby could die just after birth. Also, she can pass the disease to her developing baby who can develop serious birth defects. Make sure you and your child are protected from rubella by getting vaccinated on schedule.

Doctors recommend that your child get two shots of the MMR vaccine. Your child should get one dose at each of the following ages:. Hib mostly affects kids under five years old. Before the vaccine, over 20, kids were infected each year. Of these kids, one in five suffered brain damage or became deaf. Even with treatment, as many as one out of 20 kids with Hib meningitis dies.

Get your child vaccinated to help them beat the odds! Doctors recommend that your child get four doses of the Hib vaccine. Did you know your child can get measles just by being in a room where a person with measles has been, even up to two hours after that person has left? Measles is very contagious, and it can be serious, especially for young children. Because measles is common in other parts of the world, unvaccinated people can get measles while traveling and bring it into the United States.

Doctors recommend that your child get two doses of the MMR vaccine. Infants 6 to 11 months old should have one dose of the MMR shot before traveling abroad. Infants vaccinated before 12 months of age should be revaccinated on or after their first birthday with two doses, each dose separated by at least 28 days.

Whooping cough, or pertussis, is a highly contagious disease that can be deadly for babies. Whooping cough can cause uncontrollable, violent coughing, which often makes it hard to breathe. In babies, this disease also can cause life-threatening pauses in breathing with no cough at all. Whooping cough is especially dangerous to babies who are too young to be vaccinated themselves.