Nepal floods: How DNA identification of bodies works

DNA testing helps identify bodies that may be unrecognisable due to mutilation and decomposition.

Police personnel in protective suits carry the body of an unidentified victim of the flash floods for storage at a crematorium in Kathmandu, Nepal [Dar Yasin/AP]

More than a week after a glacial collapse near the Langtang Lirung mountain peak set off devastating floods in Nepal and Tibet, sending a deluge of rocks, mud and water to the valleys below, forensic experts are working to identify bodies.

More than 1,270 people have been killed, and more than 4,700 are still missing, authorities said on Thursday . On Friday morning, reports emerged that two of the hundreds of workers trapped in tunnels at hydropower projects along the affected rivers had been rescued.

list 1 of 4 Exclusive access as the search for Nepal’s tunnel workers intensifies

list 2 of 4 Photos: Symbolic funerals held in Nepal for missing flood victims

list 3 of 4 Rescue efforts continue as Nepal-China flood death toll rises to 1,280

list 4 of 4 Families perform symbolic funerals for missing Nepal flood victims

Meanwhile, authorities are using DNA testing to try to identify hundreds of bodies that have left morgues overflowing. Officials are urging first-degree relatives – fathers, mothers, sons, or daughters – of those reported missing to provide fresh blood samples for DNA profiling, police have said.

For missing foreign nationals, a first-degree relative (also a father, mother, son, or daughter) abroad can also undergo DNA profiling in their home country and email the results to Nepal Police for comparison. Hundreds of DNA samples have so far been collected from relatives.

The samples collected are being sent to the Nepal Police Forensic Science Laboratory and the Nepal Academy of Science and Technology.

So why is DNA identification important in the aftermath of the floods and how does it work?

Why is DNA testing needed?

In Nepal’s capital, Kathmandu, forensic teams are working to identify bodies – but many have been found in a state of decomposition, said Al Jazeera’s Jessica Washington, reporting from a DNA testing facility in the city.

“Forensic teams on the ground told us that there are some things that can help with the identification process, such as tattoos and jewellery, but many bodies were found in such a state that it is very challenging to identify them,” said Washington.

Decomposition is why DNA testing becomes essential, say experts: mutilated bodies often become unrecognisable, especially after prolonged submersion in water.

DNA profiles can be generated from blood, soft tissue, bone and teeth. According to Kerstin Montelius, a molecular biologist at Sweden’s National Board of Forensic Medicine, DNA material can still be extracted from bone even if most of the tissue has decomposed.

“Visual identification might be impossible at an early stage of the process, with confusion as a result,” Montelius told Al Jazeera. But, she cautioned, “DNA degrades, too, and circumstances set the decisions.”

How does DNA testing work?

The globally recognised framework for managing and identifying disaster victims is Interpol’s Disaster Victim Identification (DVI).

DNA molecules contain the information all living cells in the human body need to function, and apart from identical twins, who share almost the same DNA, each person’s DNA is unique. As such, it can be used to identify disaster victims or missing people.

As a part of the DVI process, human remains are inspected by specialists to detect as much biometric data as possible.

“There are three primary methods of identification that have shown to stand by themselves with a high score of probability in the identification process: DNA comparison, fingerprints and teeth comparison,” Montelius said, adding that the method chosen depends on the circumstances.

When a direct DNA profile of the missing person is available – for example, a missing person’s DNA sample can be taken from personal items such as toothbrush or hairbrush – the unidentified body’s DNA profile is compared with that of the missing person to see if they match.

However, sometimes there are “no fingerprints of the victim anywhere, or it could be difficult to find information on the teeth at the dentist’s”, said Montelius.

In such cases, DNA profiles can also be collected from victims’ next of kin, said the molecular biologist. In Nepal, that is being done through blood samples.

Once the data is collected, a team of specialists compares and reconciles the two sets of information – from the next of kin, as well as the human remains found – to identify the victims.

This can be done in one of several computer systems on the market, with the system able to suggest matches for the DNA expert to scrutinise, said Montelius.

Identification can be declared if there is a 100 percent match between the two sets of data.

Are other countries helping?

India has sent a 19-member forensic team that began a DNA sample analysis alongside their Nepali counterparts at the Nepal Police Central Forensic Science Laboratory and the National Forensic Science Laboratory, according to the Indian embassy in Nepal’s capital.

“The team is working to expedite the processing of DNA samples in Nepal for the identification of those affected by the recent flash floods,” the embassy said.

China has also sent a second contingent of DNA identification experts, alongside a third batch of emergency relief supplies, the state-run Xinhua news agency reported on Thursday.

DNA检测有助于识别因残缺和腐烂而无法辨认的尸体。

在尼泊尔加德满都，身穿防护服的警察人员将一具身份不明的山洪遇难者遗体抬往火葬场存放。[Dar Yasin/AP]

一周多前，朗塘里隆山峰附近的冰川崩塌引发尼泊尔和西藏的毁灭性洪水，大量的岩石、泥浆和水涌入山谷，法医专家正在努力辨认遇难者遗体。

当局周四表示，已有超过1270人遇难，超过4700人失踪。周五上午有报道称，数百名被困在受灾河流沿岸水电站隧道中的工人中，已有两人获救。

列表 1/4：独家报道，尼泊尔隧道工人搜寻行动正在加紧进行

图2/4：尼泊尔为失踪洪灾遇难者举行象征性葬礼

（共4条记录中的第3条）尼泊尔-中国洪灾死亡人数升至1280人，救援工作仍在继续

列表 4/4：尼泊尔洪灾失踪者家属举行象征性葬礼

与此同时，当局正利用DNA检测技术试图确认数百具遗体的身份，这些遗体已使停尸房不堪重负。警方表示，官员们敦促失踪者的直系亲属——父亲、母亲、儿子或女儿——提供新鲜血液样本进行DNA分析。

对于失踪的外国公民，其在国外的直系亲属（父母、子女）也可在其本国进行DNA检测，并将结果通过电子邮件发送给尼泊尔警方进行比对。目前已收集到数百份来自亲属的DNA样本。

采集的样本将被送往尼泊尔警察法医科学实验室和尼泊尔科学技术院。

那么，为什么在洪水过后进行DNA鉴定如此重要？它是如何运作的？

为什么需要进行DNA检测？

据半岛电视台记者杰西卡·华盛顿在尼泊尔首都加德满都一家 DNA 检测机构报道，法医团队正在努力辨认尸体，但许多尸体已经腐烂。

华盛顿说：“现场法医小组告诉我们，有些东西可以帮助进行身份识别，例如纹身和珠宝，但许多尸体被发现时的状态使得身份识别非常困难。”

专家表示，尸体腐烂是DNA检测变得至关重要的原因：残缺的尸体往往会变得无法辨认，尤其是在长时间浸泡在水中之后。

血液、软组织、骨骼和牙齿都可以提取DNA。瑞典国家法医委员会的分子生物学家克斯汀·蒙特利乌斯表示，即使大部分骨骼组织已经腐烂，仍然可以从中提取DNA。

蒙特利乌斯告诉半岛电视台：“在早期阶段，目视识别可能是不可能的，这会导致混乱。”但她也提醒说：“DNA也会降解，而且具体情况也会影响最终的决定。”

DNA检测的原理是什么？

国际刑警组织的灾难受害者识别（DVI）是全球公认的灾难受害者管理和识别框架。

DNA分子包含人体内所有活细胞正常运作所需的信息，除了拥有几乎相同DNA的同卵双胞胎外，每个人的DNA都是独一无二的。因此，DNA可以用于识别灾难遇难者或失踪人员。

作为 DVI 流程的一部分，专家会对人类遗骸进行检查，以尽可能多地检测生物特征数据。

蒙特利乌斯说：“目前有三种主要的识别方法，它们在识别过程中具有很高的概率，可以独立发挥作用：DNA 比对、指纹比对和牙齿比对。”他还补充说，选择哪种方法取决于具体情况。

当能够获得失踪者的直接 DNA 图谱时——例如，可以从失踪者的牙刷或梳子等个人物品中提取 DNA 样本——将身份不明尸体的 DNA 图谱与失踪者的 DNA 图谱进行比较，看看是否匹配。

蒙特利乌斯说，但有时“受害者身上根本找不到指纹，或者在牙医那里很难找到牙齿信息”。

这位分子生物学家表示，在这种情况下，也可以从受害者的近亲那里采集DNA样本。在尼泊尔，这项工作是通过血液样本进行的。

数据收集完毕后，一个专家团队将比较和核对两组信息——来自近亲属的信息以及发现的人类遗骸的信息——以确定受害者身份。

蒙特利乌斯说，市面上有很多计算机系统可以做到这一点，这些系统能够向 DNA 专家推荐匹配结果，供其仔细审查。

如果两组数据完全匹配，则可以确定身份。

其他国家是否在提供帮助？

据印度驻尼泊尔首都大使馆消息，印度已派出一支由 19 名成员组成的法医小组，与尼泊尔警察中央法医科学实验室和国家法医科学实验室的尼泊尔同行一起，开始对 DNA 样本进行分析。

“该团队正在努力加快尼泊尔境内DNA样本的处理速度，以便识别近期山洪暴发的受害者，”大使馆表示。

据新华社周四报道，中国还派出了第二批DNA鉴定专家，以及第三批紧急救援物资。