Viruses typically invade our bodies through an opening. Think gastrointestinal flu, COVID-19, AIDS. Our bones, however, are normally protected from any outside exposure, so they should be safe, right?

The short answer is yes and no. Of course, knowledge is power, and we need both right now, so here is a nuanced answer.

Patients with smallpox frequently complained of bone pain. Epidemics in Prague in 1891-1892, in Boston a decade later, in the Philippines a few years after that, and in India in the 1940s led investigators to conclude that bone and joint changes appeared in approximately 1 percent of infected adults and 5 percent of infected children. The elbows were affected in 80 percent of cases, hands, and wrists in 20 percent, other areas less commonly. Over half of these patients had more than one joint affected. In children, the affliction frequently halted the development of growing bones, leaving some remarkably short.

The good news is that the World Health Organization declared the worldwide eradication of smallpox in 1980. This came about by vaccinating populations with smallpox’s less virulent cousin, cowpox, imparting immunity to both. (Cow in Latin is vacca, hence the origin of the word vaccine). In areas where most people had been vaccinated, infections became rare, and routine immunization ended in the US and Western Europe in the early 1970s and worldwide in 1986.

People also got bone infections from chickenpox, but those were most likely caused by bacteria that entered the bloodstream through itchy skin blisters and scabs. Fortunately, chickenpox has become extremely rare since the advent of a vaccine in the 1990s.

The same is true for two other viral diseases that many people, myself included, tend to confuse: German measles and measles, also known respectively as rubella and rubeola (as if that clarifies things). Rubella causes milder symptoms than rubeola, but when the rubella virus passes from a pregnant woman to her fetus, the devastation includes heart defects, learning disabilities, and bone weakening, especially around the knee.

Rubeola, conversely, made patients more miserable at its onset, but it usually left bones alone. Fifty to eighty years later, however, some people developed Paget’s disease, also known as osteitis deformans, which, even without much knowledge of Latin, suggests its nature: excessive bone breakdown followed by disorganized new bone formation. Investigators have recently found a rubeola virus protein in the bone-remodeling cells in people with Paget’s disease. To study the possible link further, the researchers genetically engineered mice to harbor this viral protein in their bone cells. The mice developed Paget’s disease. On a positive note, the human incidence of Paget’s disease of bone has declined in recent decades, which coincides with the introduction of a rubeola vaccine in 1969.

Other viruses can cause aching muscles and swollen joints but do not seem to affect bone. Notorious ones of this sort cause dengue fever. It is also known as breakbone fever because it causes excruciating muscle aches. One victim-related, “You don’t die from it, but you wish you could.” There are five forms of this virus, and surviving one form imparts long-term immunity from it but not the other forms. A vaccine that covers four of the varieties is available. Dengue viruses still infect almost 400 million people annually, mostly in Africa and South America. It is lethal for one person in ten thousand (40,000 per year), most often young children, whose immune systems are not fully developed.

So back to the question, do viruses infect bone? And more broadly, are there lessons here to apply to the current COVID-19 pandemic? Yes and yes. Some viruses historically have affected bone, but there are vaccines available to prevent such diseases entirely. COVID-19 causes muscle aches, but nothing so severe as those encountered with breakbone fever, and only time will tell whether the novel coronavirus will cause bone manifestations, which may not be revealed for decades. A vaccine will become available against COVID-19, and we can hope that one form will suffice in contrast to the multiple forms needed to prevent dengue fever.

Certainly, the current pandemic is devastating on many levels, but here is some perspective. Smallpox vexed people for well over 2,000 years and killed 300 million people in the twentieth century. The Spanish flu killed up to 100 million people worldwide and nearly 700,000 Americans in just a few years. Ordinary seasonal influenza kills 300,000 to 650,000 people a year, including 60,000 Americans. Dengue fever is agonizingly painful and kills young children. Until the 1950s, the causes for these drastic diseases were unknown, no testing was available, and there were zero intensive care units and respirators. So despite present and fully justified concerns, we (including our bones) have a lot to be thankful for.

Stay immunized. Stay separated. Stay safe.

Roy A. Meals is an orthopedic surgeon who blogs at About Bone. 

Image credit: Shutterstock.com