Infectious diseases

Infectious diseases – Statistics

Even though the mortality rates caused by infectious diseases have decreased, the number of deaths caused by pathogens and parasites is only falling slowly: from 1990 with 16 million deaths per year until 2010 with 15 million deaths per year, the number of deaths has only fallen by 1% per year.

The World Health Organization (WHO) predicts 13 million deaths by infections and further 10 million deaths - more than currently die from cancer - worldwide by drug resistant infections by 2050, unless action is taken. The majority of these deaths are caused by only a few pathogens.

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From 1990 with 16 million deaths per year

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until 2010 with 15 million deaths per year

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The rising antibiotic resistance and the lack of new antimicrobial agents decelerates the reduction of deaths caused by infections. Within the last 50 years, only two new anti-bacterial drugs have been developed, both antibiotics against Staphylococcus and other gram-positive organisms (with pre-existing resistance).

Tuberculosis is re-emerging

Previously controlled diseases such as tuberculosis are beginning to re-emerge, bringing with them highly antibiotic-resistant M. tuberculosis strains.

Acute and chronic infections

Bacteria can sleep
Bacteria can "sleep"

A well-adapted pathogen which lives in balance with its host, causing only minimal harm may cause chronic infections. Bacteria causing chronic infections are able to 'sleep' and persist for a long time without needing anything but space. Even antibiotics can't harm them since they don't divide or metabolise anything. Only if the host’s immune system weakens do the bacteria eventual wake up and trigger disease.

This might happen, if an acute infection is on its way. This kind of infection is distinguishable through its rapid and dramatic onset. Among the most dangerous acute infections are respiratory infections, which lead to high mortality rates, in particular in children in developing countries (~ 4 million deaths in 2002), followed by the chronic infection HIV and the acute infection diarrhoea.

Pseudomonas aeruginosa
Pseudomonas aeruginosa

The worldwide distribution of antibiotic-resistant bacteria is a fundamental threat to mankind.

The particularly dangerous highly-resistant bacteria are found in hospitals. Here, these bacteria, e. g. Pseudomonas aeruginosa, meet weakened immune systems and can result in death. Each year, 2.5 million infections occur in hospitals, including 90,000 deaths in Europe alone. The patients enter a vicious cycle of taking antibiotics to fight against the infection or as a prophylaxis, destroying the protective microbiome and promoting the development of further resistance, thus creating more superbugs which eventually kill the host because neither the immune system is able to combat them, nor is any effective antibiotic left to administer.

Healthy people, who have an intact microbiome, can only be infected if they are invaded by a 'big army' of an infectious agents (viruses or bacteria in most cases). In this case, the immune system and the microbiome have to recruit their 'soldiers' to fight the infection, but until the fight is over, we (the hosts) are sick in bed while the battle rages on.

The situation is different for immune-deficient people, also meaning a damaged microbiome.

In this case, merely a few bacteria or viruses are sufficient to cause infection; these bacteria might even be living on that person already. Immune-deficient patients either suffer from a chronic disease, such as HIV, autoimmune disorders or cancer and most often include infants, pregnant woman and elderly people or people whose damaged microbiome is still regenerating after antibiotic therapy from the previous weeks or months.

Antibiotics weaken your immune system
Antibiotics weaken your immune system

That's right, an antibiotic-therapy that may have cured an acute infection earlier (if it was caused by bacteria) but that also weakens the patient's ability to fend off the next pathogen as it has killed the good commensal bacteria, which are the best defence against invading pathogenic bacteria. For a person with an intact microbiome, hundreds of thousands of bacteria have to invade to cause an infection, whereas for persons who underwent antibiotic therapy, only a few bacteria are enough to induce serious infection. This phenomenon has been observed in humans as well as in experiments on mice.

People who have taken antibiotics some time before a wave of infection are more likely to become infected (in fact, to a near lethal degree) than those who haven't taken antibiotics before.

Back in the 1950s, Marjorie Bohnhoff and C. Phillip Miller observed this event during a series of experiments conducted to investigate the gut microflora of mice. They infected the mice with Salmonella enteritidis, a causative agent for heavy diarrhoea in humans. In order to cause an infection in healthy mice, they needed to inject as many as 100,000 bacteria. A second group of mice received an antibiotic (Streptomycin) before infection, and they got salmonella a few days later. For these mice only 3 bacteria were enough to induce infection! This is a 30,000-fold difference! The scientists further investigated on this subject and found similar results with different antibiotics. Even if the antibiotic-administration had already taken place weeks before, still only a few bacteria were enough to induce infection.

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