The men of Israel indulge in sexual immorality with Moabite women and are led into idolatry. God sends a plague because of their disobedience. (See 2 Pet 2:15, Jude 11, Rev 2:14 for New Testament insights into Balaam and his involvement in the Israelite downfall.)

As the plague is associated with the men having forbidden sexual relations, Luke favours a sexually transmitted disease (STD) as its cause. This STD seems to be fatal within a few days to a week since Paul, almost certainly referring to this plague, tells us that 23,000 of the 24,000 people died on one day (1 Cor 10:8).

All the STDs we know of today (eg HIV, syphilis, gonorrhoea, chlamydia, chancroid, lymphogranuloma venereum, granuloma inguinale, trichomoniasis, herpes and hepatitis B) either did not exist in the ancient world or are not fatal within the time period specified.

However, patterns of disease and human susceptibility to infections 1500 years BC may have been different from today. One only has to think of South American Indian tribes being decimated by viral infections to which the Spanish Conquistadors who carried them were resistant. We may, therefore, be dealing with an STD which was particularly virulent in the Israelite population. We could alternatively be dealing with a now unknown STD or an infective agent transmitted during close contact but by another route.

Whatever the infective aetiology we can be sure that had Israel obeyed God's pattern of life-long exclusive sexual relationships (Gn 2:24) the plague would never have started. Jesus explained the full extent of this creation ordinance in the New Testament (Mt 19:1-12). In the present day the World Health Organisation is advocating a biblical pattern of sexual relationships to halt the spread of HIV. God isn't a killjoy - there are good reasons behind his laws!