With the serious migrant situation continuing to unfold across Europe, and the continuing movement of migrant populations across borders in North America, I am frequently asked if international refugees and other international migrants are factors in the dissemination and possible introduction of infectious diseases into their destination countries. The basic answer is quite easy: Of course they can be factors, and frequently are! But this simplistic answer only addresses one facet of a multifaceted and complex situation. The more complete answer is that human migrants of all sorts have always been and always will be accompanied by their parasites and pathogens. I expounded further on this in my presidential address to the American Society of Parasitologists a few years ago, excerpted here:

Trichuris trichiura egg Image/David Bruce Conn
Trichuris trichiura egg
Image/David Bruce Conn

“At first glance, no other species, throughout any of Earth’s history, seems to come close to rivaling the capacity of Homo sapiens for dispersal and colonization of new habitats. The exceptions, of course, are the other species that we intentionally, or unintentionally, take with us as we disperse. These include the plants, animals, and microbes that we take with us as sources of food and fiber—the livestock, the fish, the poultry, and so on. Also included are the parasites—those that live on and in us, those that live on and in the species that we move around with us, and especially those that use both we and our food animals and companion animals as hosts. Since there are apparently more parasitic organisms than free living, these parasites must be actually the ultimate invasive species, using their lowly human and synanthropic animal hosts as vehicles for their own dispersal. Except for the pets or companion animals, we don’t really want to take the other species with us. But we have no choice—we have to eat. And we certainly don’t want to take the parasites with us. But we seem to have no choice here either—the parasites are just too adaptable, too ingenious, too good at staying with us despite our greatest efforts to leave them behind.” (Link to full article here)

So, the next question is often whether this dissemination of disease is a valid and prudent reason for closing borders and otherwise preventing entrance of refugees and other migrants. My answer to that is also easy: Of course we should never fail to assist fellow humans in need just because they may be sick, and thus may bring sickness to us. Again, this is simplistic, and requires further elaboration.

This universal reality that pathogens disperse with their human hosts is no more true of refugees than it is for most other groups, except that refugees might have been living in situations in which they are more likely to have common diseases because of such factors as poor hygiene, poor nutrition, or poor access to healthcare. This, of course, is no fault of their own, and as humanitarians it is up to the rest of us to work globally to improve the health of all people. We should do it for those who are sick, as well as for ourselves so that we do not also fall victim to the diseases. And, it is also a reality that international refugees make up a very small percentage of international migrants, from tourists to those traveling for business, to those traveling for international sporting events, and more. All can and do bring their diseases with them.

But, we must act wisely, recognizing that all sorts of challenges confront every country in determining the best immigration policies. There are health concerns, as well as concerns over violence, crime, stress on job markets, insufficiency of housing, shortage of food and other essentials…. and the list goes on. In many ways, the health concerns are the easiest to address, and are perhaps the most important to address given the fact that parasites and pathogens, as living organisms, will always be driven to disperse in any way they can. This is why we must engage in global health activity at all times, working together as a “humanosphere” to improve access to good health. Sometimes, it is best for such joint efforts to ensure global public health by enacting strategic disease-containment measures such as temporary quarantines or suspension of travel by those who are carrying pathogens. However, stopping dispersal of disease is not a good long-term reason to deny legitimate and peaceful human migration; to the contrary, it is a reason to ensure that migrants have immediate access to available diagnostics and treatments for their diseases. To avoid or minimize spread of infectious agents, it is also a reason ensure that such humanitarian action is integrated with complementary availability of preventive measures, diagnostics and treatment for the host populations who will take their new neighbors into their communities.

My laboratory has recently released a review and perspective of some actual circumstances of infectious diseases being imported and, in some cases, disseminated by international adoptees and refugees immigrating to the United States. The most common diseases reported in recent years through 2010 have included Chagas’ disease, giardiasis, microsporidiosis, hepatitis, measles, pertussis, tuberculosis, malaria, intestinal helminths, syphilis, and others. (Link to full article here). New situations in the last three years and in the near future will likely include Chikungunya, Zika, and others. Many of these diseases have been with us before, some never have been banished, and others are still to come for the first time. In all cases, we must recognize that the pathogens – not the infected people – are the villains to be recognized and stopped or controlled. Then, when both immigrants and their newfound neighbors are all more healthy, we can find more energy to work together to deal with the political, economic, legal and criminal challenges.

Prof. Dr. David Bruce Conn is a biomedical scientist who has conducted research, taught university students, and advised governments and industries about parasitic and other infectious diseases, invasive species, and environmental health for 40 years. (Disclaimer: Dr. Conn is a senior advisor to the U.S. Department of State on issues of health and foreign policy, but the contents of this post are his own views and do not officially represent any unit of the U.S. federal government).