January 27, 2014
CRE and TRSV: A Tale of Two Infections
By Michael D. Shaw
With winter hard upon us here in the Northern Hemisphere, our thoughts often turn to colds and flu—those usually temporary, if miserable afflictions. While we humans are only too aware of our frailty against microscopic invaders, we sometimes forget that they can still be lethal. Likewise, we sometimes lose sight of the fact that lethal infections can also affect our smallest animal friends, such as the honeybee.
Which brings us to two very different lethal infections: CRE (carbapenem-resistant Enterobacteriaceae) and TRSV (tobacco ringspot virus).
First, let’s unpack the term “CRE.” So-called beta-lactam antibiotics (and this includes many common ones such as penicillin and its derivatives) all contain a structure referred to as a beta-lactam ring in their molecule. They kill the bugs by inhibiting synthesis of the cell wall. However, some bacteria produce the enzyme beta-lactamase, which breaks down the ring, and therefore the antibiotic itself. Interestingly, the enzyme has been around since the dawn of time, and is not specifically an adaptation to the antibiotics.
Now, carbapenems are a type of antibiotic that can foil the beta-lactamase enzyme, owing to a carbon atom being substituted for a sulfur atom in the ring. Enterobacteriacae is a family of bacteria that includes Escherichia coli and Klebsiella pneumoniae. For several years, carbapenems have been used as the antibiotic of last resort for infections of Enterobacteriacae.
At some point, perhaps in the 1980s, bacteria containing enzymes that could also destroy the carbapenem ring were first identified, although they were virtually unknown in the United States before 1992. Thus, we have carbapenem-resistant Enterobacteriaceae, or CRE. With the last resort antibiotic being knocked out, it is no exaggeration to say that CRE are a serious threat to public health. Indeed CRE infections have been associated with mortality rates as high as 50 percent.
CRE infections tend to occur in health care settings. According to the CDC, patients whose care requires devices such as ventilators, urinary or intravenous catheters, and patients who are taking long courses of certain antibiotics are most at risk for CRE infections.
Infection control expert and friend of this column Lawrence Muscarella, PhD has followed CRE infections for years, including the recent largest in US history outbreak, at Advocate Lutheran General Hospital in Park Ridge, IL. According to the hospital, the infections could be traced to improperly processed GI endoscopes. As a result, the hospital changed from high level disinfection to ethylene oxide gas sterilization of the scopes, and claims that this solved the problem.
Maybe. Muscarella wonders how rigorously that contention has been validated, and has further concerns regarding individuals who could be “colonized” with CRE, but remain asymptomatic. Do we have a reincarnation of Typhoid Mary, walking around with CRE? Do we have, as he puts it, a “microbial time bomb”? More than that, can CRE colonize (but not infect) a well patient, who undergoes a colonoscopy? There’s a scary thought, and one that probably won’t be studied any time soon.
Moving on to TRSV, this rapidly mutating RNA virus is a nasty plant pathogen. Aided by its nematode vectors, TRSV affects many species, with bud blight of soybeans being the most significant. If that weren’t bad enough, all indications are that TRSV is the cause of bee colony collapse disorder. First identified in 2006, the main symptom is either no or very few adult bees present in the hive; a live queen is there, but there are no dead bees. Often there is still honey in the hive, and immature bees are present. Varroa mites, a virus-transmitting parasite of honeybees, have frequently been found in affected hives.
A new study published by the American Society for Microbiology determined that pollen-borne TRSV was replicating inside the honeybees and spreading to the Varroa mites, which infect other bees. The researchers note that traces of the virus were detected in every part of the bees examined, except their eyes.
As you might expect, the Greenie fear entrepreneurs were trying to pin the blame for the collapse disorder on pesticides—in this case neonicotinoids. But a pathogen cause was always more logical, and now it seems quite likely. Only don’t hold your breath waiting for the anti-pesticide crowd to walk back their claims.
In the meantime, if you really want to be scared about something, consider what could happen if TRSV “host shifts” to humans. According to the referenced study: “Emerging and reemerging diseases that result from pathogen host shifts are a threat to the health of humans and their domesticates. RNA viruses have extremely high mutation rates and thus represent a significant source of these infectious diseases.”