The disease, also known as the sickness, is the cause of the disaster. It affects people over the age of 14 (or 16 if reading the US version). It is unknown for certain how the sickness works but, it's likely it is a parasitic infection and kids under 16 don't have it because they were not born when the parasites were in their "spore" stage and spread across the world. It is believed that the parasites originated from the Inmathger tribe in South America. When scientists discovered the tribe they carried the disease to the rest of the world, hidden in their blood. The parasites mimicked human cells and spread. (They even affected eggs and sperm and were passed down to the Twisted Kids.) After 14 to 16 years of hiding the disease "bloomed" to cause the outward symptoms of sickos. Nearly a year and a half after the "bloom" the sickos are massing for another potential "spore" stage. The parasites themselves are little worm-like grey bugs that exist in grey jelly, often stored in the brain.

Symptoms and other affectsEdit

Stages of the disease:

1) Basic fever symptoms such as cough, cold, blemishes, tonsillitis and a mild fever.

2) Blistering, swelling, boils, black nails, yellow eyes and grey skin. Loss of self control also occurs at this stage.

3) Burst eyes, warty tongue and a unrecognisable body. The disease causes necrosis and disfigurement.

4) Rupture of skin and organs, accelerated decomposition and necrosis, and ultimately death.


The disease is made worse by sunlight. It is revealed in The Fear that when an infected adult is exposed to the sunlight for a long period of time, the disease spreads faster and makes the victim explode. Some sickos can gain a resistance to the effects or wear things such as sunglasses to lessen the effects of sunlight. Most likely, the parasites are affected by strong UV radiation having past generations lived previously under a dense canopy in the rain forests.


In The Dead, it is described that eating children's flesh can make the sickness spread slower. Greg eats what he describes as "smoked meat", although it is really children's flesh. Drinking children's blood has a similar effect. Sickos have a clearness of mind after eating kids. In later books Wormwood explains that good blood will drive out bad blood. A few surviving children were born with an immunity to the disease and their resistances are key to making a cure.

Telepathy Edit

In The Sacrifice it becomes clear that people with the disease can communicate via telepathy or ultrasound. It is possible that the parasites are the cause of this. The frequency that is emitted by sickos is a high whining sound that only the girls could hear in The Sacrifice. In The End another louder sound is emitted by Paul while communicating with other sickos. Some sickos host stronger parasites and draw crowds of other sickos together with a hive mind. In The End Fish-Face says that she and her father nearly share a mind and can read each others thoughts.

The GreenEdit

The two stronger and more "sane" sickos (Wormwood and St. George) are obsessed by a great green and become convinced that they are angels that have been friends with wildlife. Their confused ramblings give an idea as to the origin of the disease. It may have originated from space as they say they fell from the sky and are fallen angels. The disease then worked its way up from fleas to birds to mammals and humans. (In The Enemy the monkeys in Reagent's Park are also affected.) They existed in the green, which was the jungle. An important thing to mention is that Wormwood and St. George both have split memories that they confuse. The past lives of the parasites and their own lives often get mixed up. The parasites might therefore have their own sort of self awareness or intelligence.

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