What is causing rare birth defects in Brazil? Health authorities of vast South American country have already declared that mosquito-borne Zika virus is behind the latest surge in microcephaly cases, but some health experts think the virus’ presence in the country doesn’t mean it caused the birth defect.

Last week, Mr. Arthur Chioro, health minister of the country, announced that Zika is undoubtedly behind microcephaly, but Arnold Monto, an epidemiologist at the University of Michigan, said even if Zika virus cases are rising in the country, it doesn’t mean it is causing microcephaly.

The investigation is still on and experts are trying to find a link between the virus and birth defects. It all started when a doctor in Brazil saw a dramatic surge in microcephaly among babies. The increase was followed by first outbreak of the tropical virus Zika.

Some experts say there is no link between the virus Zika and microcephaly as the region has experienced Zika outbreaks in the past as well. Microcephaly is a condition in which babies have smaller than normal head and often have a smaller brain. In some lab tests, the virus has been detected in the brain tissue some babies who took birth with microcephaly.

Dr. Ernesto Marques from the University of Pittsburgh said the investigation of microcephaly is no less than a murder case. Zika has killed many people in the past, but if it is causing microcephaly, is still to be found, Marques added.

“What you have so far, the victim is there, and you find a person right there that has a smoking gun in his hand. But you still need to close the deal”, Marques continued.

Investigators are facing some challenges as they don’t have substitute for humans to study the virus and its impact in detail.