The Initiation of Infection and the Cause of Disease (Part 3): Disseminated and Opportunistic Infections

In the field of infectious diseases, two of the most dreaded types of infection are disseminated infections and opportunistic infections. Without these two forms of infections, most diseases would easily be resolved. Co-infection is another complication, but we’ll discuss that at another date.

Disseminated infections are infections that spread away from the point of primary infection. For instance, the point of primary infection might be the lungs, but the microbes, toxins produced or immunological response might get to the heart, liver and other organs as well. Disseminated infections are the opposite of localised infections, which are infections that do not spread beyond their primary sites of infection.

Much about disseminated infections has already been discussed in this article; kindly read through it. I will try and focus on opportunistic infections; even though it had also been discussed in this other article, I will try to relate the topic to the present discussion. Opportunistic infections are those infections that occur due to the immunocompromicity of an individual. Like their names imply, they are infections that use the opportunity that the immune system is down to quickly colonise a part of the body system and establish infection.There are so many ways this could happen, and we will systematically look at them.

One, as written in this article on the normal microbiota that live on/in our body, sometimes, their loss or reduction (largely due to indiscriminate uses of antibiotics) can lead to an external microbe colonising the organs they left. Also, if one of these indigenous microbiota survives the attack of antibiotics, its sudden growth and proliferation can be disastrous.

Let me make it more practical. In our guts, we have several gut microbes collectively called coliforms. Examples of these coliforms are Escherichia, Serratia, and Citrobacter, Enterobacter and Klebsiella. They exist in our gut in a mutualistic form of relationship, and they compete among themselves for space and nutrients; this helps to keep their numbers in check, leading to a sort of balance. They are also recognised by our immune system as part of self, so they usually don’t get attacked. However, a reduction or loss in the numbers of any of them will automatically lead to an increase in the numbers of the rest due to lack of competition and availability of space. Once this happens, the balance is tipped, and infection occurs. The abuse/misuse of antibiotics is a also primary cause of this, which can kill the residential microbes, paving way for colonisation of ingested, large microbial load of external microbe, for instance, Salmonella typhi.

This also happens in the skin, which contains over a thousand species from about 20 groups of bacteria. And since the skin has three main ecological areas namely sebaceous, moist, and dry, the kind of microbiota found in some areas are different from other areas. A loss or reduction of the residential microbes in an area can lead to colonisation of that area by the other microbes, leading to infection. This is why Staphylococcus, a microbe present on the dry and sebaceous parts of the skin, can cause infection if it replaces Lactobacillus, another microbe found in the moist areas of the skin like the genital area.

Even in the genital areas, where Lactobacillus (a bacterium that makes the genital area of female acidic) co-exist with Candida (a yeast-like fungus), a reduction or loss of Lactobacillus through aggressive washing (called a particular name here in Nigeria), will lead to the population of Candida exploding. This is the primary cause of Candidiasis (yeast infection in the vagina, oral thrush in the mouth). The last part of that statement also points out that if a microbiota from an area of the body, gets to another part of the body, it can also cause infection if the area is conducive enough for it.

Let me stop here. Other future articles will talk about the rest. From now till then, stay healthy. Cheers.

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Updated: February 24, 2021 — 12:00 am

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