Novel Pathogens Come Out of Old Stories

In late 2019, Chinese doctors noticed an unusual number of cases of acute respiratory distress syndrome (ARDS). ARDS can be caused by a wide variety of issues ranging from pancreatitis to brain injuries to severe pneumonia. The condition went through several layers of scientific description before we reached the point today where it is called COVID-19. With COVID-19, these layers happened in a matter of weeks, but the story of zoonotic coronaviruses goes back much further than that.

Today, the World Health Organization estimates that 75% of new diseases are zoonotic, that is, like the examples here, they are shared between animals and people. A growing understanding of the importance of One Health principles helps us be less surprised when these pathogens reach humans and more prepared to respond to them. One Health recognizes that the health of humans, animals and their shared environment is closely related.

Let’s look at the names and histories of three zoonotic pathogens: the viruses SARS-CoV-2 and HIV and the bacterium Bartonella bacilliformis. At first glance, the lengths of the histories of these pathogens seem very different: the first known record of B. bacilliformis is 2,000 years ago, while the first record of HIV is in 1981 and the first record of SARS-CoV-2 (the virus that causes COVID-19) is 2019. However, each of the newer pathogens has echoes that go back much further.

This wasn’t always expected to be the case. In 1972, microbiologists Macfarlane Burnet and David White predicted, “the most likely forecast about the future of infectious diseases is that it will be very dull.” This expectation was of course very wrong. And every disease that would come to the forefront since—ever-mutating coronaviruses, HIV, and more—already had their development underway in the environment when they wrote that.

For the three pathogens discussed here, the following animal relationships are important:

SARS-CoV-2	There was already an awareness that bats are a perfect host for novel human pathogens. Consequently, the environment has to be changed to reduce contact between bats and people.
HIV	HIV came from SIV, a virus that infects chimpanzees. Awareness of diseases shared between humans and primates means that more work is done to protect both from sharing diseases with each other.
Bartonella bacilliformis	An animal reservoir for this bacteria has never been found. There has even been some speculation this could be an unusual case where there is a plant reservoir, but that has never been found either. All we know is that it is carried and spread by sand flies (Lutzomia verrucarum) located in South American countries such as Peru, Ecuador, and Columbia.

There may be future diseases that we cannot even begin to imagine. But what we can imagine is that these diseases will likely come from places in the environment where humans and animals meet.

Could there be other diseases circulating unknown among us already? Researchers believe that Mycoplasma haemohominis, found in primates and humans and discussed previously in relation to bats, may be responsible for deaths whose cause is currently unrecognized.

An example of a surprising pathogen was H. pylori, responsible for many stomach ulcers and yet unknown until the early 1980s. H. pylori has also been linked to stomach cancers since its discovery. The American Cancer Society suggests about 2 out of 3 adults worldwide are infected with this bacteria, but the majority do not develop stomach cancer.

Although the exact mechanism in humans is unclear, it is thought that ulcers can lead to changes in the inner lining of the stomach that make cancer more likely. Furthermore, researchers have shown that H. pylori can convert nitrites from food or water into compounds that cause stomach cancer in lab animals. If we think of “stomach ulcer” as an alternative name for H. pylori, how many centuries back might the knowledge of H. pylori go?

The history of coronaviruses, HIV, and Bartonella bacilliformis each follow a similar path. At first, they were known by names for what scientists could describe at the time. Only later did it become clear exactly what the pathogen was, and then names for the pathogen and for the diseases it causes took their current form. These histories are listed below.

Human coronaviruses:

Name	Description
Croup	Croup, a barking cough that generally affects children and sometimes adults, was first described in 1765. It is now known to be associated with a variety of viruses, including the coronavirus HCoV-NL63.
B814	In 1965, the first description was given of a human coronavirus, B814. It was collected from the respiratory tract of an adult with the cold and proven to be the cause of the cold by infecting volunteers. About 20% of colds are caused by a few coronaviruses that continually circulate in the human population.
Infectious bronchitis virus of chickens	In the late 1960s, researchers discovered that a virus that infects chickens was similar to B814.
Coronavirus	Also in the late 1960s, the group of viruses was named “coronavirus” because of it’s crown-like appearance. By now viruses in this family had been discovered to be the cause of mouse hepatitis, transmissible gastroenteritis virus of swine and other diseases. In the years since, a variety of coronaviruses have been found in bats, but they’ve also been found in other animals including a whale. In 1975, coronavirus was officially accepted as a genus of viruses.
2003 severe acute respiratory syndrome outbreak	This illness was caused by the coronavirus SARS-CoV.
2012 Middle East respiratory syndrome (MERS) outbreak	These illnesses were caused by MERS-CoV. Partly because the disease was named for a region but was later not contained that that region, the next virus would not be named for a region.
2015 MERS outbreak in South Korea	Same as above.
2018 MERS outbreak	Same as above.
Acute respiratory distress syndrome (ARDS) cluster	At the end of December 2019, people associated with the Huanan Seafood Market in Wuhan, China began to get sick with a severe pneumonia called ARDS.
2019-nCoV	On January 7th, 2020 Chinese health officials announced they had isolated the pathogen responsible. It is named 2019 novel coronavirus.
Novel Coronavirus Pneumonia (NCP)	This is the name Chinese health officials gave the cluster observed in Wuhan, China.
SARS-CoV-2	On February 11th, 2020, the International Committee on the Taxonomy of Viruses announced the name of the novel coronavirus.
COVID-19	On February 11th, 2020 the World Health Organization announced that the name of the disease caused by SARS-CoV-2 is COVID-19. This name comes from “coronavirus disease 2019” but is not an abbreviation of that term, rather it is its own name.

HIV: 

Name	Description
SIV	In the 1920’s, colonialism brought merchant and sexual trade to the Belgium-controlled Congo. A variety of sexually transmitted diseases were noted, but not specified. Retrospective research traced several instances of Simian Immunodeficiency Virus (SIV) making the jump from chimpanzees to humans. Some of these variations remained endemic to the region, but one ended up traveling around the world.
Pneumocytis carinii pneumonia (PCP) cluster	This cluster of infections in previously healthy gay men was described in an article published by the CDC on June 5th, 1981.
GRID	A new disease called gay-related immune deficiency (GRID) was first noted in print on May 11, 1982.
AIDS	It quickly became apparent that the disease was not confined to gay men. The name of the disease was updated to Acquired Immunodeficiency Syndrome in a CDC publication on September 24th, 1982.
Retrovirus	Researchers at the Pasteur Institute discover a retrovirus that could be the cause of AIDS and published a report on May 20, 1983.
HTLV-III	Researchers at the US National Cancer Institute identify the retrovirus responsible for AIDS and named it. Another researcher separately identify the retrovirus and name it LAV.
HIV	On May 1st, 1996, the International Committee on the Taxonomy of Viruses announced that the virus previously known as HTLV-III and LAV will be called Human Immunodeficiency Virus (HIV). As additional varieties of HIV were discovered it became HIV-1.

Bartonella bacilliformis:

Name	Description
[Unknown]	Skin nodules caused by vasoproliferative disease appear on a carved human figure from South America that is more than 2,000 years old.
Peruvian Warts	This is a later name for the skin nodules caused by the disease.
Carrion’s disease	A periodic fever that appeared in the region was not connected with the skin nodules until 1885. In that year, Daniel Alcides Carrión Garcia infected himself from a nodule to prove the connection. He died and the disease was later named after him.
Oroyo fever	In 1905, as many as 10,000 workers on the La Oroyo-Lime railway in Peru died from a fever. Dr. Alberto Leonardo Barton Thompson found bacteria in their blood. At the time, the bacteria was considered a member of the genus Rickettsia.
Bartonella bacilliformis	In the early 1990s, the genus was split off from Rickettsia and named for Dr. Barton Thompson
Bartonellosis	The current scientific name for diseases caused by Bartonella species developed in the 1990s as other species of Bartonella were identified in patients with AIDS.

Conclusion

Novel viruses and bacteria tend to make the mainstream news only when an important medical discovery or an outbreak that affects large populations occurs. However, clinicians, veterinarians and researchers are constantly taking note of new disease manifestations and trying to understand the associated pathogens better. Understanding the history of pathogens and how they relate to others can be beneficial for developing better diagnostic tests and treatments.