An aHUS Trigger- S. Pneumoniae

Most of the aHUS community are aware that aHUS is the result of predisposing genetic factors ,some known some not yet known, and precipitating conditions, or triggers , of the disease coinciding. Streptococcus Pneumoniae ,or S Pneumoniae, or even pneumonococcus  is one such trigger.

S. Pneumoniae are bacteria , first identified long ago by Louis Pasteur in the 19th century. There are over 90 types of the bacteria, some inhabit our  nasal cavities and rarely, if ever, do any harm. Some invade the body and cause serious illnesses such as pneumonia, sepsis and meningitis. These illnesses are predominantly seen in very young children and much older adults.

Some of the bacteria are more virulent than others. Just less that 10% of the different strains of the bacteria cause around 66% of the incidence of streptococcal infections. Some of the bacteria have capsules around them, these are the ones that can cause most problems to the immune system.

Complement plays a vital part in the immune response to invading bacteria but some strains of streptococcus have developed chemical evading techniques on the surface of their capsules and the bacteria can avoid the attack on them, The attack comes from something in doctors’ speak called “phagocytosis”.  Effectively the bacteria gets eaten. Click here to see an illustration of phagocytosis in action.

The incidence of invasive pneumonococcal disease (IPD)  is rare , just less than 100 per million of the population are affected each year in western world countries. That would mean over 30,000 cases in USA and 50,000 cases in Europe each year. Over 90% of them children.  This level of incidence however reveals the success of vaccination against IPDs. Just a couple of decades ago there were 10 times that level of incidence.

The annual incidence of aHUS is around 0.5 per million,and so it is much rarer . A small number of aHUS incidents are triggered in patients experiencing an IPD.

So for these unfortunate individuals not only do they suffer the consequences of sepsis or meningitis, but they also have the impact of a TMA to contend with. It is  a version of aHUS sometimes called SP-HUS.

SP-HUS was first identified nearly 50 years ago as being something which is different to HUS caused by a virus Escherichia coli  or E. coli

Treatment for HUS depends on what is accessible including dialysis , plasma therapy or eculizumab.

Treatment for SP-HUS from IPD requires antibiotics too , but success is being limited by antibiotic resistant strains of S. Pneumoniae.

In its research agenda ( more info here) the aHUS community has identified predisposing and precipitating factors as something to be catalogued and understood, particularly their risks between individuals.

S. Pneumoniae triggered aHUS is very rarely likely to happen*. Vaccination has reduced the risk for all patients, so no less for those with complement dysregulation issues too. Those known to be predisposed to aHUS have an opportunity to protect themselves from a trigger.

More research is needed on genetic and other characteristics of those who have encountered this trigger in their aHUS onset. It could  help others with risk based prevention strategies.

*In the unlikely event that someone  who has experienced SP-HUS should read this  blog they would be welcome to write something about it. Contact the alliance at info@ahusallianceaction.org.