Cienciaes.com: Cruella Legionella | Science Podcast

2021-08-02 19:48:51

This week we are going to revisit an episode of an epidemic outbreak in Spain that, fortunately, only remained an outbreak and did not constitute a major problem. It is an infectious outbreak by the bacterium Legionella pneumophila, which happened in the region of Murcia in the summer of 2001. Listen carefully, because what I was saying at that time will surely remind you of certain things that are happening today. In mid-July 2001 he said the following:

Here is a summary of the article:

The outbreak of Legionella pneomophila that took place in the Murcian capital has once again sowed alarm and raised concerns among citizens.
The bacterium that causes legionnaires’ disease rose to prominence in 1976, where it preyed on the 200 members of a Legionnaires’ convention (hence its name) in Philadelphia, USA. Thirty-four of them died. From that date, Legionella has spread throughout the world.
The question that the warned reader will ask is: why was the disease declared in 1976 and not before? Is the disease caused by a new species of bacteria, unknown to date, that could have arisen due to the irresponsibility of some scientists in manipulating microorganisms by playing sorcerer’s apprentices?
The explanation lies in the interaction of a bacterium, probably much older than the human species itself, which has taken advantage of a change in the environment that man, with his intelligence or stupidity, has caused.
Legionellas are fragile bacteria that cannot last long in the open air, or rather, in open water, and they need to infect and enter other cells to survive and reproduce. The usual host of this parasite is an amoeba, a unicellular microorganism also typical of aqueous media. The Legionella is allowed to be phagocytized, that is to say “eaten”, by this cell, but the bacterium has learned to avoid being digested by the amoeba and, on the contrary, uses it to reproduce inside it. When reproduction reaches a high number of bacteria, the amoeba dies, ruptures and releases its bacterial load abroad, which will seek new hosts to reproduce.
Technological progress that has brought us air conditioning, hot water, saunas, yacusis (or however you want to write that in Spanish), has also provided new ecological niches where, if not cleaned and maintained correctly, the Legionellas They can reproduce freely. Cooling towers in large buildings, in particular, use water for cooling, and the warm, moist air that is replaced by cold air is released to the outdoors in the form of aqueous aerosols. These, like a cloud, are suspensions of small water droplets, some of which carry a dangerous bacterial load inside.
Unprotected citizens can breathe in these aerosols and thus carry the bacteria into their lungs. Heavy smokers are more likely to have this happen because the cilia in the lung, which prevent particles from entering the lung, are damaged. One more reason to quit smoking, now. Once in the lung, the bacteria begin to reproduce, now we will explain how. After a few days of incubation, the patient begins to experience symptoms: high fever, shortness of breath, chills, dizziness and cough with thick sputum, on occasions. If not treated immediately, the disease can lead to death, which may be the result of an induced misdiagnosis because the symptoms of legionellosis are similar to those of the flu.
What does Legionella do in the lung to cause us so much trouble? Exactly the same as it does in its natural habitat: find a cell that it can colonize in order to reproduce inside it. Of those we have many in the lung. These are the macrophages of the pulmonary alveoli, cells of the immune system that are there precisely to prevent infections by engulfing, that is, eating, any microorganisms that may reach the body through the airways. As with the amoeba, Legionella allows itself to be engulfed by the macrophage and once inside it reproduces. This process produces two phenomena. First, macrophages, which detect the infection, flock to the lung, which instead of helping, can make the disease worse because the bacteria find more cells in which to reproduce. On the other hand, these cells release substances that, in an attempt to harm the bacteria, also damage the lung itself. Legionella, in turn, also produces harmful substances that help it colonize more cells and also damage the lung. Thus, Legionella did not appear, as if by magic, in 1976. What appeared around that time was a change in the environment, the formation of aerosols, which favored its expansion. One more lesson on how environmental modification can affect us all for good or bad.

What has happened since then?

Research on Legionella has remained at good levels since the bacterium was identified in the Legionnaires’ convention outbreak in 1976. This is a good indication that the public health problem posed by Legionella is still relatively far from being resolved. . In Spain, before and after the outbreak in Murcia in July 2001, which is the largest in the world, there have been other less intense outbreaks that also caused deaths. In Spain, the first occurred in Benidorm, Alicante province, in 1980. In 1996, there was also a serious outbreak in Alcalá de Henares, Madrid province, with 224 affected and 10 deaths. Other outbreaks after this one thankfully never reached its level of severity. However, according to a report by Diario Veterinario, published in 2020, the cases of legionellosis in Spain, far from decreasing, are increasing, and this despite the containment measures that are used.

Some information that would complete the data mentioned above may be of interest. First of all, more than 50 species of bacteria of the genus Legionella are known today. L. pneumofila is the one that causes 90% of the cases of infection, but four other species are responsible for the remaining 10% of the infections. About 80% of cases occur in people older than 50 years, and about 65% are men.

The sources where the Legionellas can be located are very diverse. It has been documented that Legionella can be found in air conditioning towers (which was the origin of the Murcia outbreak), swimming pools, showers, ice machines, refrigerators and refrigerated cabinets, spas, hot springs, dental equipment not properly sterilized , and even car windshield washer fluid.

Perhaps the most interesting discovery about this bacterium is the one recently published this month in which I record this, July 2021, by a group of researchers from the universities of Zurich and Basel, in Switzerland. Researchers are studying the molecular mechanisms by which bacteria decide that it is time to kill the cell they inhabit, because it is already too old or weak, and go in search of new host cells. Bacteria do this through the process called quorum sensor, which leads them to change the way their genes work and become different and more pathogenic bacteria than those that inhabit the cell interior.

The quorum sensor is the ability of many species of bacteria to communicate their status and at the same time detect the status of neighboring bacteria in a population. This allows bacteria to make molecular decisions by consensus or by democratic majority by modifying the functioning of genes to act on their situation and change it in their favor. This quorum sensor consists of a complex mechanism that is not completely known in the case of Legionella. Their knowledge could allow the development of drugs and antibiotics that interfere with their functioning and prevent Legionella from leaving the cells in search of new ones, spreading the infection and, on the contrary, dying inside its host, which would thus become a prison sentenced to life imprisonment.

As I said, research on Legionella and many other dangerous bacteria continues, and this must be the case if we want to, firstly, fully understand their biology and, secondly, act on them to prevent them from harming us. There is no vaccine against Legionellosis, which would certainly be welcome.

Jorge Laborda (08/02/2021)

Works by Jorge Laborda.

Your defenses against coronavirus