The Zika virus, which is spreading with alarming rapidity in Latin America, is probably causing some pregnant woman who are exposed to it to have babies born with a birth defect called microcephaly. The babies are born with, or grow up with, abnormally small heads and may have a range of developmental problems. 

Advice from the World Health Organisation and national health services is that women should avoid getting pregnant for the time being. This is a problem in strongly Catholic Latin America, as the Catholic Church teaches that contraception is wrong. These countries also have highly restrictive abortion laws, often severely limiting and criminalising the practice. Calls by the UN for these restrictions to be lifted have not gone down well with the Catholic heirarchy, with Peru's Cardinal Cipriani likening it to Herod's slaughter of the innocents. 

The 'conservative' position of the Catholic Church when it comes to abortion and contraception is coming under attack. Secular writers are portraying the Church as a callous institution uninterested in the welfare of thousands of mothers and their potentially disabled children. 

However, many secular writers – and liberal Christians too – have failed to engage with the Church and haven't understand the theology behind its position. 

OK, so what is this theology?

Before we get to the specifics of abortion and contraception, it's important to understand the worldview behind the Catholic Church's approach to this. 

The foundation of the way that Catholics think about sex, and consequently abortion and contraception, is Natural Law. This is an ethical system first developed by the philosopher Aristotle and developed further by Christian ethicist and philosopher St Thomas Aquinas.

It first asks what our human nature is, and then looks to what guiding principles can be derived from this nature. 

The single guiding principle is this: "good is to be done and pursued, and evil is to be avoided". From this, all the primary precepts of how to fulfil the human purpose are derived.

These precepts are:

1. Protect and preserve human life

2. Reproduce

3. Educate your children

4. Know God

5. Live in society

That's a lot of theory. What does it actually mean?

For instance, in the context of marriage, it is good to have children because sex naturally results in pregnancy. Similarly, we shouldn't go around killing innocent people because of life's innate value, as we are made in the image of God.

What does this have to do with the Zika virus?

These primary precepts – which according to Natural Law are self-evident – are then prompts for secondary precepts, which are derived using practical reason.

One of the examples used by Aquinas in his Summa Theologica is "killing the innocent" because this directly goes against the primary precept to "protect and preserve human life".

This is where things begin to get a little interesting.

Most people will agree that taking innocent life is categorically wrong. Where the Catholic Church challenges the liberal consensus is on its view of what constitutes life, its value and when it begins.

The Catholic Church believes that "human life is sacred because from its beginning it involves the creative action of God and it remains forever in a special relationship with the Creator, who is its sole end. God alone is the Lord of life from its beginning until its end: no one can under any circumstance claim for himself the right directly to destroy an innocent human being" (Donum Vitae, 5).

The Catechism of the Catholic Church says that "human life must be respected and protected absolutely from the moment of conception. From the first moment of his existence, a human being must be recognised as having the rights of a person – among which is the inviolable right of every innocent being to life."

It holds a genuine belief that the abortion of a foetus is the destruction of an innocent life, and therefore a direct contradiction of the primary precept to protect and preserve human life.

What about microcephaly?

The legalisation of abortion has been the focus for many activists involved with the Zika virus outbreak, due to the potential effects the virus has on the unborn foetus.

The condition linked to the virus – microcephaly – causes babies to be born with abnormally small brains. Some are calling for the expansion of legal abortions in Brazil to include deformed foetuses and are condemning the Church for its 'conservative' position on the issue. However, the Church response is that just because someone might be born with a disability doesn't mean that their life is not worth living or that they are somehow disposable. The National Conference of Brazilian Bishops released a statement explicitly condemning the efforts of groups to legalise abortions in the case of deformed foetuses as "an utter disrespect for the gift of life."

On therapeutic abortions, Cardinal Oscar Rodriguez Maradiaga of Honduras, coordinator of Pope Francis' group of nine cardinal advisers, told La Tribuna: "therapeutic means curative, and an abortion doesn't cure anything, it takes innocent lives away".

Because of the belief that life is sacred, that it begins at birth and that it is a gift from God, the Catholic Church is not going to budge on this issue. It would be disingenuous for the Church to say that abortion is a legitimate response to the Zika virus when it holds that that would involve ending a life of infinite worth. Every pregnancy involves risk and there is always potential for a child to be born disabled, but his or her intrinsic value is not dependent on its health.

In fact, the Zika virus doesn't present any new theological challenges to the Church. It has always known that some babies might be born with disabilities, and always resisted calls to allow them to be aborted.  

And the reality is, 65 per cent of the Brazilian population is Catholic and 79 per cent of them do not want abortion legalised, according to a 2014 Ibope Institute poll.

So, the Catholic Church won't budge on abortion and the Brazilian population doesn't really want it to. What next?

What is crucial to the understanding of the Catholic Church in Brazil is that, although it does not see the solution in abortion, it is deeply concerned about the Zika virus, and with issues of health care and poverty more generally.

While activists have focused a lot of the conversation on abortion, there is a more interesting discussion to be had around contraception.

But I thought Catholics didn't like contraception either?

You are correct. Because the act of sex naturally has the potential for procreation there is a primary precept to procreate. The secondary precept bans contraception, except for natural forms, including abstinence and the dubious rhythm cycle.

So, they're not going to support contraception as a means of avoiding microcephaly either then?

You would have thought so, and you are right that it is not seen as the ideal; abstinence is seen as the best way to avoid getting pregnant in high risk areas.

However, the Arcbishop of Sao Paulo last week referred to the use of condoms as a "personal choice" in an interview with the BBC, and distinguished it from abortion because it "does not involve a formed life."

He is not a lone voice on this. For one thing, in contrast to the Brazilian people's affirmation of the Catholic position on abortion, 71 per cent of Catholics support contraception, according to a 2005 IBOPE study. Ninety four per cent support condoms as a way of preventing disease.

In 1972, the Mexican bishops recognised that Catholic conscience might require "responsible parenthood", particularly in the context of "a very real and excruciating emergency for most Mexican families – the population explosion".

Speaking on the AIDs crisis in a book-long interview and the use of condoms to combat it, Pope Benedict said that although it is not "a real or moral solution, but, in this or that case, there can be nonetheless, in the intention of reducing the risk of infection, a first step in a movement toward a different way, a more human way, of living sexuality".

So is the Catholic Church ready to endorse contraception?

That is unlikely. However, it is around the issue of contraception rather than abortion that there is room for a productive conversation. Birth control is an issue that does not directly concern the killing of an innocent life and is far more accepted by the Catholic laity. There is possibility of movement on this subject, whereas on the issue of abortion, if life is a God given gift, clearly it is never something that can be ended on "therapeutic" grounds.