Urban pigeons, a potential health risk


Recently a friend argued that Paul McCartney is not a good guitarist. Hey, it's not even on the Top 100 list of Rolling stone, in which his former teammates George Harrison (in 11th place) and John Lennon (55) do appear.

My answer was: McCartney is not a good guitar player, compared to who? The list of Rolling stone, even assuming a rigorously objective value (which is not the case), it only shows that there have been at least 100 better guitarists in the world than the former Beatle. How many millions of guitarists are worse that he? Disqualifying McCartney from the position of an amateur is at least presumptuous, but above all it is to lose sight of the perspective of the context: many bands in the world, even among those who criticize him, would like to have a guitarist like Paul McCartney.

And what on earth does Paul McCartney have to do with pigeons and zoonoses (diseases transmitted from animals to humans)? You may wonder. To assess McCartney's skill with the guitar, or the risk of transmission of pigeon diseases, with proper perspective, it is essential to place the object of assessment in context: compared to what? Yes, pigeons can transmit diseases to humans, and in fact it happens. But What is the real risk? How often does it happen?

Image by Craig Cloutier / Flickr / CC.

Let's go back to the study at the University of Basel that I quoted yesterday. The authors combed the data and have the answer: Between 1941 and 2003, the total documented cases of human infections caused by pigeons was… 176. In 62 years, 176 cases. Do you know how many people die in a traffic accident in just one year, specifically in 2013, the latest data published by the World Health Organization? 1,250,000 Even assuming that the 176 cases of pigeon infections had ended in death, which is not the case, we could estimate that in a year more than 446,000 times more people die on the road than because of the pigeons. Which suggests that we should be 446,000 times more concerned about the health risk of cars than pigeons.

Of those 60 pathogens that pigeons could transmit to us, there are only documented cases of transmission to humans for seven of them. None of them, none, of Campylobacter (That bacterium present in more than two thirds of Madrid pigeons analyzed in that alarming alarmist study that I mentioned yesterday). Most of them, from Chlamydia psittaci Y Cryptococcus neoformans. The authors of the Swiss study concluded: “although domestic pigeons pose a sporadic risk to human health, the risk is very low, even for humans involved in occupations that put them in close contact with nesting sites. ”

But let's return to the results of the study on Madrid pigeons. Apart from in this species, where else can we find the Chlamydia psittaci and the Campylobacter jejuni? Regarding the first, and although psittacosis is known as parrot disease because of its first description in these animals, the truth is that it is very common in birds: According to a 2009 review written by Belgian researchers, it has been described in 465 species. And among them, you can already imagine that the bird is more directly related to the consumption habits of infinity of humans: the chicken, or the chicken.

For example, a 2014 study on Belgian farms found that in 18 of 19 facilities analyzed the psittacosis bacteria was present, or rather bacteria, since recently other related species that also cause the disease have been discovered. Periodically investigations, such as one carried out in 2015 in France, discover that the disease has jumped from chickens to farm workers. Luckily, psittacosis is cured with antibiotics. And although the transmission from person to person is possible, it is very rare. Turkeys can also be a source of contagion: the authors of the 2009 review cited that this bacterium is endemic in Belgian turkey farms, and therefore it is probably also in many other countries.

But also Campylobacter jejuni, the other microbe detected in Madrid pigeons and that can cause diarrhea in humans, is raised very comfortably in poultry farms. In 2017, a study of faecal samples in Dutch facilities found a prevalence of this bacterium of 97% in laying hen farms, and 93% in those raising chicken for meat. The authors verified that in more than a quarter of the cases the microbes expand to the soil and surrounding waters, and cited the fact that 66% of cases of campylobacteriosis in humans originate in chickens, followed by 21 % caused by cattle. Pigeons do not appear as a source of any contagion.

Of course, with all of the above, there will be someone tempted to conclude that the pigeons in particular, but also the birds in the broadest sense, are "rats with wings." Well, and although most cases of registered campylobacteriosis come from chickens, these animals are not really the greatest possible source of infection with these bacteria: a new review published precisely a few days ago reminds us that “The species of Campylobacter they can be commonly isolated in faecal samples collected from dogs and cats. ”

That is to say, the bacterium whose presence in the pigeons was so crowded (or chirped?) By that study in Madrid is very common in dogs and cats, who takes their dog to the park looking suspiciously at the pigeons, should Know that possibly your own animal is a carrier of this bacterium. Of course, as I have insisted, the risk of contagion in any case is really low. However, it is appropriate to quote the author of the new review: "Contact with dogs and cats is a recognized factor of human campylobacteriosis, and therefore people who live or work in close contact with dogs and cats should be advised of the zoonotic organisms that these animals can release. ”

In fact, Campylobacter It is far from the only dangerous pathogen that can be found in the most popular companion animals. If we said yesterday that pigeons can transmit 60 diseases to humans, The US Center for Disease Control (CDC) lists 41 pathogenic organisms that dogs and cats could infect people, including bacteria, viruses, fungi and parasites, but clarifying that it is a selective list, not exhaustive.

Now, and in case there was someone inclined to think that pigeons, birds in a broader sense and companion animals are "rats with wings or legs", it should be added that neither house animals are the only possible source of contagion. Today, the school that does not take its students to visit a farm-school is rare. Well, in 2007 a review in the United Kingdom collected numerous cases of disease outbreaks caused by excursions to these enclosures, and discovered that many common zoonoses are also present in farm-schools.

With all this it is not a matter of alarming about any risk of contagion from contact with animals, but quite the opposite, to explain that the real danger of contracting a disease due to pigeons is similar to that caused by any other animal that lives with us, and that in any case the risk is very low, as long as the recommended hygienic measures such as hand washing are respected.

But it should be remembered that even for pets strictly under veterinary control, as required, Some experts point out that a dog's lick can lead to our living tissues, such as wounds, eyes or mucous membranes, pathogenic microbes that their tongue or snout have collected before other undesirable places: "Dogs spend half their lives stuffing their noses in dirty corners and sniffing excrement, so their snouts are full of bacteria, viruses and germs," ​​said virologist at Queen Mary University in London John Oxford.

Max Pixel image.

Of course, in case there is a nihilist willing to ensure that pigeons, birds more broadly, companion animals and all animals in general are "rats with wings or legs", It is essential to clarify that the main source of infection of infectious diseases in humans is none other than humans themselves. These infections are commonly transmitted among us by routes such as breathing sprays or contact with contaminated surfaces, but let's not forget that "human bites have higher infection rates than other types of wounds" because "human saliva It contains up to 50 species of bacteria, ”recalled a 2009 review.

Are we doves, birds in the broadest sense, companion animals, all animals in general and humans in particular "rats with wings, legs or legs"? It would be quite unfair to rats, I recover what I told in this blog four years ago about a study that analyzed the presence of pathogens in New York rats:

Fourteen of the rats studied, about 10% of the total, were completely free of dust and straw. 23% of the animals had no virus, and 31% were free of bacterial pathogens. In fact, among all the possible situations that combine the number of viruses with the number of bacteria, that of zero viruses and zero bacteria turns out to be the most prevalent, the one with a higher percentage than the rest. Only 10 rats were infected with more than two bacteria, and none of the 133 with more than four. Only 53 rats had more than two viruses, and only 13 more than five. Taking into account that, especially at this time of the year, there is no human who is free from a flu (influenza) or a cold (rhinovirus), and adding the occasional fever and other herpes, some papilloma and hepatitis, in addition to Epstein- Barr that almost all of us carry or have carried (and not counting bacteriophages, endogenous retroviruses and others), It seems that after all we are not much cleaner than rats.

It turns out that finally not even rats are "rats with legs". And as I also told here, these rodents show in the laboratory studies a capacity for empathy with members of their own species that sometimes we lack to humans. But if there are species there with surprising abilities, among them are also the pigeons: before looking at them with disdain, Know that these animals are able to distinguish Bach's music from Stravinsky's. How many humans can do the same?

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The infectious diseases that pigeons can transmit to humans is not something common since direct contact with this bird or with its droppings is necessary, one of the main routes of transmission.

But that does not mean that these animals do not transmit diseases through infectious agents such as viruses, fungi and bacteria that cause allergies and respiratory ailments. These are the most common pathologies:

Psittacosis or Chlamydiosis

The Chamydia Psittaci bacterium is responsible for psittacosis, a disease usually transmitted by parrots, parakeets and parrots, although pigeons can also be infected and become transmitters of this bacterium to man by respiratory tract, nasal secretions, feces or tissues and pens, according to a publication of the Institute of Food and Agricultural Sciences of the University of Florida (United States).

This disease causes in men similar to pneumonia and influenza and even digestive ailments because this bacterium penetrates the body through the respiratory tract and spreads through the bloodstream to invade the lung, spleen and liver .

Psittacosis is a disease more common in people who are in direct contact with birds, such as those who work in poultry plants.

Pigeon droppings can be a route of infection of salmonella, a bacterial infection that can reach through contaminated food and even by clothes, explains Manuel Pizarro, professor of pathology at the Faculty of Veterinary Medicine Complutense University of Madrid and bird specialist.

The picture it causes in humans is fever, diarrhea, nausea, vomiting and abdominal pain.

It is an allergic reaction, a hypersensitivity to the feathers and fecal dust of the pigeons and is produced by a continuous exposure of an individual to these birds, such as those working in a hatchery performing house cleaning tasks.

It causes inflammation of the alveoli of the lungs and the symptoms are cough, shortness of breath, fever and chills. It can be confused with a cold.

Crytococcus Neoformans is a fungus that is located in the pigeon droppings. Actually the reservoir (where the fungus is lodged) is the soil with the excrement and not the animal.

According to the study of the University of Florida, the transmission is produced by inhalation of yeast similar to fungi, although it can occur occasionally by ingestion.

Humans can acquire this disease if they are in contact with the nests of the pigeons where parasites and lice of these birds are also concentrated.

Cryptococcosis in humans manifests as meningitis or meningoencephalitis and is usually preceded by a lung infection with cough, blood sneezing, fever and malaise.

The pigeons have acclimatized perfectly to the urban habitat where they install their nests in any roof or recess of the buildings of the cities or towns and where they feed in containers, landfills, wheat fields and cereals.

These birds can reproduce several times between the months of March and August and usually have one or two chicks at a time.

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Pigeons can transmit multiple infectious diseaseseven with fatal consequences for lung damage, pneumonia, hepatitis or brain condition, reported the Ministry of Health (Minsa).

"Their feathers, their droppings, among other agents of these birds, transmit fungi, bacteria and parasites"said Ana María Navarro, national coordinator of the Zoonosis Strategy of Minsa.

The most affected, according to the specialist, are children, older adults, people infected with HIV, cancer patients and diabetes because their defenses are diminished.

He explained that the greatest danger it is the direct contact to the excreta and the inhalation of the same in the form of microscopic dust.

The specialist indicated that there are reports of more than 40 diseases transmissible among which are: Salmonellosis, colibacillosis, cryptococcosis and histoplasmosis. In addition, pigeons are carriers of ectoparasites such as lice and ticks.


People affected by these types of diseases may have:

- Fever, chills, sweating, myalgia, anorexia.
- In digestive conditions it is manifested by vomiting, enterocolitis, headache, weakness.
- Acute infections accompanied by dehydration.


- Control the Proliferation of these birds decreasing food availability.
- Cleaning areas with pigeon droppings should be done with disposable gloves and appropriate clothing.
- Wash the area with plenty of water to avoid exposure to dust.
- It is not advisable that people who have their weakened immune system, perform that type of cleaning.
- Local authorities must issue ordinances and strengthen health education to prevent the proliferation of pigeons.


Pigeon droppings can be a route of salmonella infection, a bacterial infection that can reach through contaminated food and even by clothes, explains Manuel Pizarro, professor of pathological anatomy at the Faculty of Veterinary Medicine of the Complutense University from Madrid and bird specialist.

The picture that causes in humans is fever, diarrhea, nausea, vomiting and abdominal pain.

Allergic alveolitis

It is an allergic reaction, a hypersensitivity to the feathers and fecal dust of the pigeons and is produced by a continuous exposure of an individual to these birds, such as those working in a hatchery performing house cleaning tasks.

It causes inflammation of the alveoli of the lungs and the symptoms are cough, shortness of breath, fever and chills. It can be confused with a cold.