Although I don’t make that much use of them in my campaigns, disease spirits are among the biggest dangers in Glorantha. The average disease spirit has a POW of 16-17 and has about a 2/3rds chance of infecting an average person with an acute version of the disease they carry, and better than 1/3rd chance of the serious version.
The disease stays with the victim until the victim recovers, dies, or the spirit is forced out. If the victim dies, sometimes that creates a new disease spirit in addition to the original one. A dozen or so disease spirits released in a village can quickly spread into a pandemic.
Additionally, exposure to “pollution” can result in diseases.
Dealing with disease, and the risk of disease outbreaks, is the primary function of many Chalana Arroy temples. Healers treat the ill, fight disease spirits with their Rune magic, summon healing spirits, and the like. That’s where I suspect most of those Rune points get spent – not on Resurrection or Heal Body, but on Cure All Disease, Summon Healing Spirit, and Restore Health, and is why Healing Trance is more popular than Heal Body. The cult is big enough and numerous enough that diseases can be kept mostly under control, but it still might be the biggest killer in Glorantha (a point of pride to the Death goddess Mallia no doubt).
Now this is bad enough without broo and the Mallia cult, but they actively and intentionally release disease spirits, pollute streams and other sources of water, and so on. Mallia is hated and feared – and feared enough that many are willing to become involuntary members in order to not die. Fighting Mallia is something Orlanth and Yelm are in perfect agreement with!
And thus although death from childbirth and infancy is likely much lower in Gloranthan societies than the ancient world (one more reason people love Ernalda!), disease, war, and famine are much more prevalent than in modern societies. One more reason to fear Mallia (and Humakt and Daga), and one more reason to love Chalana Arroy, Ernalda, and Dendara!