I’m doing some research on Morocco’s history during the early 17th century, and more specifically the chaos leading to the fall of the Saadians Dynasty. One of the main causes, if not the main, is the death of the sultan Ahmad al-Mansur in 1603. He is known as a Sultan even though he claimed the title of caliph (who is considered as an Islamic Emperor) after conquering the Songhai Empire in eastern Mali (which no other Moroccan ruler has attempted before or since) and stopping the expansion of the Ottoman Empire in West Africa. His vision of forming an Islamic Caliphate led him to divide his kingdom between his three sons making each one of them a Sultan after his death. Unfortunately for him, things didn’t go as expected.
First, by the end of the sixteenth century, the kingdom was hit by a deadly plague. The first wave of the epidemic struck between 1597 and 1598, disturbing his rule. As preventive measures al-Mansur abandoned his palace in Marrakech and ruled from tents in the countryside.
Between 1599 and 1601, the plague and its fatalities abated but resumed the next year. In 1602, his favorite son Al-Shaykh (ruler of Fez) rebelled against him with the intention of taking the throne. Forced to leave his tents in the countryside, al-Mansur headed to Fez with his army to fight his son. He managed to stop the rebellion and Al-Shaykh was imprisoned. Al-Mansur who was ruling from tents outside the city of Fez, which was the most hit by the plague, got infected and died in 1603.
Zaydan who was left with the power in Fez was recognized as a successor by local notables. But the notables of Marrakech did not recognize him and proclaimed Abu Faris. The three sons started a civil war that, with the help of the plague and the famine, plunged the country into years of darkness and chaos.
Now onto the question, Al-Mansur raised an army to attack his son in 1602, and after his death, his sons raised multiple large armies to attack each other with the armies reaching sometimes 40,000 men. While the plague ended in the year 1608, with the years 1598 & 1603 considered the worst years of that plague wave (I've read in some sources that the sultan before his death have replaced his guards and servants with slaves so things were pretty bad) and considering that by 1598 the plague took the lives of at least 450,000 Moroccans:
How was the plague affecting the armies, and how were they dealing with it while marching to war?