Zika fever is a horror. It’s a mosquito-borne disease that is almost undetectably mild in adults but in pregnant women can cause terrible defects in their babies. There is no cure, and none in sight. We can be grateful that the mosquito species that carry the disease do not range in much of Europe, nor in most of Asia. But the fever has already crossed the Pacific from Africa to South and Central America and threatens to spread north to the USA. Like most mosquito-borne diseases it is primarily an affliction of the poor. There is nothing wrong with the taste of rich people’s blood, but they can afford running water, air conditioning and protective netting, which all cut the risk of mosquito bites. If those fail, the rich can simply move away from the areas where the disease is endemic. No one who can help it lives in a malarial marsh.

Zika is frightening enough in its effects but what’s almost worse is its unexpectedness. It caught the world’s public health agencies by surprise, and its dangers were only detected by accident in Brazil when there was a sudden surge in the number of babies born with undeveloped heads and brains, a condition known as microcephaly. We are still not sure of the nature of the link between microcephaly and the fever. It seems clear that there is one, but the mechanism is unknown and may involve another factor besides the virus. Because Zika has been known only in countries where the rates of infant mortality are high and record keeping for the most part dreadful, there is little material for comparison.

One lesson from this crisis is that the global health community must be on the alert for dangers that are hard to imagine and so even harder to detect. An epidemic like Ebola is much easier to detect, however hard to get under control. Some of the early reactions smack of panic. Several Latin American countries are advising that women avoid pregnancy for several years and it’s difficult to imagine any gesture more futile. It makes excellent sense for pregnant women to avoid putting themselves in danger of infection, but for women who are already in danger of infection to avoid pregnancy is an entirely different strategy, and it’s not going to work.

Poor women in poor countries have very little control over their own fertility. Their lives and their bodies are too often controlled by men. That’s a deep-rooted social fact, which cannot be worked around by simply handing out contraceptives. Women everywhere should have choice and agency over their own bodies, and hormonal contraception such as the pill does need to be much more widely available. But westerners can’t assume that other women will make the choices we would prefer: that’s rather the point about giving other people choice. Poor women will make the same choices as rich ones do only when their incentives to do so are the same. The word “family” in “family planning” is not just padding. So a change to fewer, later babies is one that requires a transformation of a whole culture, in which men become convinced of its merits quite as much as women do.

The other choice not available in this situation is safe and legal abortion. The diagnosis of microcephaly in the womb is not possible without ultrasound equipment even in countries were abortion is reasonably cheap and widely available, and it can’t be made early. What will almost certainly happen instead is a rise in neonatal mortality – infanticide by deliberate neglect or ruthless action – in all those countries where the virus rages. This is tragic and dreadful but those babies will not be saved until a reliable, cheap and easily distributed vaccine becomes available. That will not happen for years, if it ever does. In the meantime, the best defence is an attempt to eradicate the disease-bearing mosquitoes from around human settlements. It’s slow, unglamorous and not entirely effective – but it is entirely necessary. Heroic medicine makes better copy, but in the end it is public health which saves more lives.