A novel model for malaria contagion involves the mechanism of a mosquito entering a residence where multiple people are sleeping in one room. The way that the infection spreads is that a mosquito bites an infected person and then moves over to bite an uninfected person, thus transmitting the disease vector. Someone at one time suggested the simple idea of placing mosquito netting over each bed, thus making it hard for a mosquito to (1) get through the netting, (2) bite a sleeping person, (3) get back through the netting, (4) get through the next sleeping person's netting, (6) bite that person, and (7) get back through that netting.

That's a 6-stage Markov chain (the 7th doesn't factor) with a small probability at each stage versus a 2-stage Markov chain with no netting at all.

I remember reading about this a while ago and have not been able to find a definitive citation, but this one is close

> Graves, P.M., Ngondi, J.M., Hwang, J. et al. Factors associated with mosquito net use by individuals in households owning nets in Ethiopia. Malar J 10, 354 (2011). https://doi.org/10.1186/1475-2875-10-354

I recall that the idea originally came about because someone was wondering why malaria is not prevalent in North America even though the climate is well suited for it. In fact [malaria was prevalent here early on](https://www.mosquitosquad.com/greater-dc/about-us/blog/2014/august/history-of-malaria-in-the-usa/) :

> "Changes in living also contributed to the establishment of malaria in America as people settled in towns and villages. Inhabitants were living in closer quarters, sharing space with domesticated animals and travelling less thus passing the disease onto family and neighbors. The growing of rice in pools of stagnant, shallow water commenced in the Carolinas, creating an ideal habitat for mosquitoes. Poor sewage and drainage also produced an environment for the parasites to live in and breed."

But then when the culture changed and family members got their own individual room to sleep in, the disease went away. At least that's the way I've heard it explained, and that's how the individual mosquito net idea was sold. Families in Africa and elsewhere still aren't wealthy enough to have multi-room homes but they can get the individual sleeping nets.

So the mosquito net stochastic model is an N-stage Markov chain run through a Mone Carlo simulation = MCMC.