Globalization and infectious disease

Definition

Before 2019, the increased ease and frequency of international trade, travel, and migration raised concerns about the potential spread of infectious diseases. Many diseases, including cholera, yellow fever, Ebola, Zika virus, and communicable meningococcal illnesses, reemerged in the late-twentieth and early twenty-first centuries, attributed primarily to the speed of international travel. These concerns were compounded in 2019 with the advent of the COVID-19 pandemic. This rapidly transmittable coronavirus caused nearly seven million worldwide deaths between 2019 and 2023.

In the twenty-first century, outbreaks of severe acute respiratory syndrome (SARS) (2003), H1N1 influenza (2009), Ebola (2014-2016), Zika virus (2015), and SARS-CoV-2 virus (2019) demonstrated the pace at which epidemics could become globalized and the potential global economic impact. This produced an acknowledgment that newly identified infectious diseases must also be contained to prevent them from becoming pandemics. In 2007, the World Health Organization (WHO) warned new diseases were emerging at an unprecedented rate of one per year. However, control of infectious diseases and prevention of pandemics was identified to require monitoring of disease patterns, adherence to international regulations, reporting to world health authorities, and international response coordination when potential epidemics arise. The impacts of COVID-19 later demonstrated the global impacts when these controls were unsuccessful in containing the disease.

Background

The spread of infectious diseases through travel and migration has presented a problem for public health as long as humans have been mobile. The best known of these diseases is perhaps the plague, caused by the bacterium Yersinia pestis. Outbreaks of plague occurred numerous times in history, and already in the fourteenth century, it was recognized as an "imported" disease. Although the germ theory of disease and modes of disease transmission were as yet unknown, it was accepted that the disease was somehow transported by travelers and in goods arriving from plague-infected areas. This realization led to the establishment of a forty-day isolation period (or quarantine) to identify infected persons, which, however, did little to stop the spread of plague throughout Europe. In time, advances in medical knowledge, improvements in living conditions, and the development of vaccination programs helped reduce or eliminate some infectious diseases.

In modern times, controlling the spread of infectious diseases has become much more complicated, and the speed and frequency of worldwide travel have made communication of potential disease events a high priority. Diseases considered regionally controlled or eradicated are being reintroduced into these areas; new infectious diseases, such as viral hemorrhagic fevers, have the potential to travel around the world in less than twenty-four hours.

Migration

The extent of recent human migration has been a significant factor in the global spread of communicable diseases. According to the Pew Research Center, in 2020, the number of international immigrants was estimated at 281 million or over 3.5 percent of the global population. This was more than three times that number recorded in 1970. Migrant workers, refugees, and nomadic groups can transport endemic diseases as they travel, often exacerbated by the poor living conditions commonly afforded these groups.

Migration has spread infectious diseases, such as dengue fever, into areas where they were not previously seen and reintroduced diseases like tuberculosis into areas where they were previously controlled. Additionally, permanent migrants change the complexion of infectious disease patterns in the host country. Migration patterns typically move from developing nations to more prosperous areas. Residents of these impoverished regions generally lack adequate healthcare, nutrition, and sanitation, making them more susceptible to contracting infectious diseases and harboring pathogenic microorganisms.

Migrants who enter host countries through official means may be subjected to medical histories and physical screening to identify infectious and sexually transmitted diseases. Their movements may be tracked through travel documents and passports. Immigrants who have entered a country by unofficial (or illegal) means have not undergone such screening and may be principal vectors for infectious diseases. Undocumented immigrants are of particular concern because they are not screened, may fear seeking treatment for any diseases they have, and may contract additional pathogens during their journey into the host country.

Chagas’ disease, caused by Trypanosoma cruzi, is an infectious disease that has been globally spread to nonendemic areas. This organism is mainly transmitted by insects; however, it can also be spread through blood transfusions, organ transplants, contaminated food, and vertical transmission. Historically, Chagas’ disease has been endemic to Mexico, Central America, and South America. After the year 2000, however, it was identified and documented in the United States, Canada, Europe, Australia, Japan, and regions of South America not previously affected. An estimated 1 to 2 percent of Latin American immigrants to Europe and the United States may be infected with T. cruzi, exemplifying a tropical disease that is now a global health concern.

The rate of tuberculosis (caused by Mycobacterium tuberculosis) cases among native-born United Kingdom residents was consistently controlled throughout the first decades of the twenty-first century. The number of tuberculosis cases among immigrants living in the United Kingdom, however, was high because of migration. While the tuberculosis rate remained consistent at approximately 4 cases per 100,000 persons for the British-born population during this interval, the rate for migrants in the United Kingdom ranged from 80 to 102 cases per 100,000 persons (approximately 72 percent of total cases). A similar, though not as drastic, pattern was observed in the United States in 2008, in which the tuberculosis rates were 2 and 20 cases per 100,000 persons, respectively, for US-born and foreign-born residents. However, the WHO reported that tuberculosis infections spiked in 2023 to the highest new infection rate since 1995, with 8.2 million people newly diagnosed and 10.8 million total infected individuals.

Although there are real disease risks caused by migration, it is also important to recognize that the majority of immigrants are not substantial public health threats. Despite the claims of some politicians that immigrants, especially undocumented ones, are a major cause of infectious disease in the United States, there is no data proving such allegations. The US Centers for Disease Control and Prevention (CDC), which monitors diseases related to border crossings, has reported very few outbreaks directly connected to immigrants. Most health experts agree that cross-border travel, illegal or otherwise, shows no evidence of causing epidemics in the United States. Furthermore, the very nature of globalization means that immigrants are only one aspect of the increasingly interconnected global community, and other factors—such as food shipment or international travel—are just as risky in terms of infectious disease as immigration.

Global Travel

Air travel has become the fastest and most efficient means of infectious disease movement across the globe. In 2023, 7 billion passengers traveled by air worldwide, and of those, 1.8 billion traveled internationally. A trip from New York City to either Beijing, China, or Mumbai, India, can be completed in about twenty-four hours. This is less time than the incubation periods of many communicable diseases. Many infectious diseases of concern are spread through airborne pathogens such as influenza, SARS-associated coronavirus, and M. tuberculosis). These are ideally suited for transmission in a contained aircraft cabin.

The SARS epidemic provides a model of international airborne pathogen transmission within an aircraft cabin. Although it did not result in a catastrophic pandemic, this disease demonstrated how an outbreak could quickly spread to multiple countries (in this case, thirty-seven) by international travelers. The disease itself has an incubation period of approximately seven days before symptoms appear, allowing it to unknowingly be transported anywhere worldwide. The index case was a Guandong, China doctor who flew to Hong Kong in early 2003. The doctor had previously treated patients in Guandong with a respiratory illness that was, at the time, unidentified. While staying in Hong Kong, the doctor transmitted the disease to several other guests staying at the same hotel. One international business traveler subsequently transmitted the disease to twenty-two other passengers during air travel. All these transmissions occurred within days and before the onset of any symptoms of the disease in the persons who were infected.

Also of concern are diseases that are considered to be controlled or eradicated in a region that are imported back into the area. Measles was considered to be eliminated from the United States in 2000 because of a vaccination program that began in the 1960s; however, since this time, there have been periodic outbreaks of measles because of international travel. In the first six months of 2008, 131 measles cases were reported to the CDC, which was about twice the number reported on average per year from 2000 to 2007. Most (89 percent) of the cases during the 2008 outbreak could be linked to international outbreaks.

At the time of this outbreak Measles remained very common in China, Southeast Asia, and, to a lesser extent, Europe. Travel to these areas or contact with foreign visitors accounted for only 17 of the 131 US cases; association with these infected persons within the United States accounted for an additional 99 cases. The source of transmission for the remainder was unknown.

Most people who contracted measles during this outbreak (91 percent) were either unvaccinated or had unknown vaccination statuses. In addition, 80 percent were under twenty years old, indicating that an increasing number of children were not being vaccinated because of religious objections or other reasons. Measles is highly contagious. It quickly resurfaces in the United States when vaccination rates decline because it is still so prevalent in the rest of the world. The 2008 measles outbreak, with the highest infection rate in the United States since 1996, illustrates the potential reemergence of an infectious disease that is considered controlled, particularly in areas with low vaccination rates.

However, further outbreaks in the twenty-first century proved more problematic. While some years experienced lower infection rates, measles infections in the US reached 220 in 2011, 667 in 2014, 1,274 in 2019, and 284 in 2024. Globally, measles cases also increased, with India, Russia, Ethiopia, and Iraq reporting over 8,000 cases in 2024. Pakistan had the highest number of infections, at over 14,300.

Infectious Disease Control

The spread of infectious diseases has been recognized as a threat to global health for several hundred years. Various health agencies have recognized this and endeavored to engage in international cooperation. The first cooperative effort to control cholera, plague, and yellow fever began in Europe in 1851, when the first International Sanitary Conference (ISC) was convened. By the mid-nineteenth century, the international shipping trade and the growth of transcontinental railroads had successfully swept the cholera epidemic throughout Europe. National regulations and quarantine were inconsistent and ineffective; cooperation among nations was the only method of monitoring and controlling disease propagation with minimal interference in international trade. Over the next century, these efforts resulted in international, legally binding regulations for international travel and transport. The ISC issued a series of regulations and gave rise to four international health agencies: the Pan American Sanitary Bureau (1902), the Office International de l’Hygiène Publique (1907), the Health Organisation of the League of Nations (1923), and WHO (1948). By 1951, these agencies had converged into WHO and issued the International Sanitary Regulations by the World Health Assembly. These international regulations expanded on the treaties issued by the ISCs.

Since the early 1950s, WHO has been pivotal in monitoring and controlling the spread of infectious diseases worldwide. The International Sanitary Regulations aimed to control smallpox, typhoid fever, relapsing fever, yellow fever, cholera, and the plague, establishing standards for reporting international travelers and goods possibly carrying infectious diseases. WHO subsequently revised the regulations to include eradicating smallpox and focusing on yellow fever, cholera, and plague. These regulations were replaced by the International Health Regulations in 2005 (revised in 2007 and amended multiple times, including in 2022), which took a broader, more fundamental approach to protecting public health. The focal points are on preventing the global spread of infectious diseases with minimal interference in international travel and trade, and on stringent reporting policies regarding any health situation that threatens public health. WHO also has programs to help member states track and respond to outbreaks that can potentially develop into large-scale epidemics.

Developed countries, especially those successful in the eradication and control of various infectious diseases, have attempted to institute health regulations on international travelers, migrants, and imports. In response to health threats posed by human migration, some receiving countries have implemented restrictions on incoming migrants from areas with endemic infectious diseases of concern. These may include health screening, proof of vaccination, and potentially, quarantine. However, border control policies are rarely effective because of the sheer volume of persons who cross international borders over any period and because of the undetermined number of undocumented immigrants around the world. Even if it were possible to examine each person at a border crossing, diseases in the incubation stage could not be detected.

Noncatastrophic epidemics such as the SARS outbreak in early 2003 provide healthcare agencies with models of the global spread of infectious diseases. Using these models and other techniques of epidemiology, the pattern of disease transmission can be predicted, allowing for the design of action plans in the event of a future infectious disease outbreak. SARS was the first example in the twenty-first century of an infectious disease outbreak that was tracked and contained by disease control measures. At the onset of the epidemic, little was known about the virus except that it could be spread by airborne transmission, that there was a fatality rate of about 10 percent, and that there were no vaccines or curative agents available. The release of public information and a global disease alert issued by WHO allowed potential travelers to be aware of the threat and to change their plans to avoid air travel or visiting areas in which SARS was identified. These actions had a substantial negative economic impact, but contact with infected persons could be minimized. Closely followed hygienic measures prevented the extensive spread of the disease among healthcare professionals. Furthermore, establishing the infectivity and incubation period of the virus facilitated tracking those persons who were infected and those who had been exposed.

In preparation for the Olympic Winter Games in Vancouver, Canada, in 2010, Canadian health authorities used known disease patterns from other mass human gatherings, such as the Hajj and the G-20 summit, to create a plan to identify and manage any potential infectious disease outbreaks. Before the Games, Canada had developed a Global Public Health Intelligence Network, a surveillance system that enabled them to acquire real-time information on potential disease threats (such as mumps, measles, and Norwalk-like virus) through the Internet. In conjunction with projected air-traffic patterns, health authorities developed models of potential patterns of infectious disease distribution. Had any infections been identified, alerts could have been issued to officials at the Games. Health officials in the native countries of visitors and athletes would also have been notified to prevent travelers from bringing any infectious diseases back from the Games to their home countries.

Beginning in 2019, the global experience with the COVID-19 coronavirus provided a stark demonstration of how the disease could be quickly transmitted throughout the planet. In mid-December 2019, patients in the Chinese city of Wuhan began to exhibit pneumonia-like symptoms that did not react to conventional forms of treatments. By the end of December 2019, the World Health Organization in China was made aware of an apparent form of pneumonia of an unknown cause that was causing patients to experience shortness of breath and high fevers. These cases seemed to be concentrated in Wuhan. By mid-January 2020, the SARS-CoV-2 virus had been reported outside of China in neighboring Asia countries. On January 20, 2020, the first laboratory-confirmed case of COVID-19 was reported in the United States in the state of Washington. Eleven days later, COVID-19 had been declared a public health emergency in the United States. On March 11, 2020, COVID-19 was declared a global pandemic after spreading to 114 countries. By June 2020, the number of COVID-19 cases in the United States was over 2 million. At the close of 2024, over 1.1 million Americans had died from COVID-19, and an estimated 110 million were thought to have contracted the virus in some form. However, vaccinations significantly decreased the mortality rate of the disease beginning in 2021. Over 80 percent of the US population was estimated to have received at least one dose between March 2021 and May 2023.

Impact

Migrants coming from developing nations typically require more health and social services and can place a tremendous burden on health services in host countries. In some receiving countries, migrants make up a majority of the population. For example, in the United Arab Emirates, immigrants make up more than 80 percent of the population. WHO recognizes that migration is not a temporary phenomenon, and that high migration rates significantly impact the nature of diseases and healthcare systems of the host countries. Therefore, it urges receiving countries to make migrant health a high priority, stressing that the health of the native population is affected by the health of migrants and their children. However, migrants have specific medical, genetic, and cultural healthcare requirements, and the cost of providing this migrant-specific care cannot be estimated.

In addition to the impact of infectious diseases on the cost of health services, they also have a surprising impact on the global economy. This is particularly true for infections in which the modes of transmission are not definitively known. In the case of SARS, which was a relatively mild outbreak, the cost to the global economy was estimated at $30 billion to $100 billion. Most of this cost was borne by the travel, tourism, and other industries. Most of this deficit was absorbed by countries that continue to rely primarily on travel and tourism for their income. On a microlevel, however, people lost their jobs and their incomes. The long-term consequences of global disease outbreaks are often continued poverty and substandard living conditions, creating ideal conditions for further outbreaks.

To prevent a catastrophic pandemic, the WHO has established regulations for monitoring, reporting, and responding rapidly to any infectious disease events. The fundamental goal for WHO and other global health agencies is to provide access to healthcare for all, with the expectation that improved health in poor areas will result in less disease transmission and overall positive global health outcomes. The human population continues to grow, focusing more on preventing the human-to-human transmission of communicable diseases.

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