MERS (Middle Eastern Respiratory Syndrome) has now spread to 16 countries since first appearing in Saudi Arabia in 2012. MERS causes similar symptoms as SARS (Severe Acute Respiratory Syndrome) -- including a fever, cough, and shortness of breath -- but is nearly three times as deadly with a 30% fatality rate. Both MERS and SARS are caused by coronaviruses, which can infect both humans and animals.

The MERS coronavirus. Source: Wikimedia Commons.

More than 500 cases of MERS have now been reported worldwide, with the U.S. reporting its first case in April. That's a sharp rise from last November, when only 153 cases were confirmed across nine countries. The WHO recently stated that the spread of MERS is a "serious concern" but not yet an "emergency," stating that it did not "see increased evidence for person-to-person transmissibility."

However, a recent report from Columbia University, King Saud University, and EcoHealth Alliance confirmed that the MERS virus originated from camels and could possibly be spread by touch like SARS. SARS infected over 8,200 people and killed 775 during a 2002-2003 outbreak.

There are no approved vaccines or treatments for MERS, but three biotech companies -- Inovio Pharmaceuticals (NASDAQ:INO), Novavax (NASDAQ:NVAX), and Nanoviricides -- are currently developing vaccines for the disease.

Inovio's approach to MERS: Synthetic DNA
Back in November, Inovio announced that preclinical tests of a vaccine for MERS showed "robust and durable" immune responses in mice.

Like most of Inovio's other pipeline candidates, the experimental MERS vaccine was constructed from synthetic DNA which is thought to be potentially safer than traditional vaccines. Synthetic DNA vaccines replicate the virus' DNA footprint to elicit an immune response, but they are not alive, cannot replicate, and cannot spread within host cells. Inovio's MERS vaccine reportedly induced levels of antibodies and T cells -- both crucial in clearing infections caused by the virus -- to rise in mice.

Inovio does not have any marketed products. Its most advanced treatment, VGX-3100, is currently in phase 2 trials for cervical dysplasia -- abnormal changes to surface cells on the cervix that can lead to cervical cancer. Inovio plans to release top-line data from that trial in mid-2014, which is considered the next big catalyst for the stock.

Inovio's most notable partner is Roche (OTC:RHHBY), which signed a deal worth up to $412.5 million with the company last September to co-develop two therapeutic vaccines for prostate cancer and hepatitis B.

Novavax's approach to MERS: Recombinant DNA
Novavax, which mainly focuses on producing vaccines for influenza and RSV (Respiratory Syncytial Virus), has also been developing an experimental MERS vaccine. However, like Inovio's vaccine, Novavax's vaccine hasn't advanced beyond animal trials yet.

Like Inovio, Novavax also avoids using weakened or killed viruses in its vaccines. Whereas Inovio creates vaccines with synthetic DNA, Novavax pieces together viruses with recombinant DNA, piecing together DNA from various sources (usually surface proteins of a virus or pathogen) to create customized vaccines to elicit specific immune responses.

Novavax's most prominent backer is the U.S. government. In March 2011, the Office of Biomedical Advanced Research and Development Authority awarded Novavax a contract valued up to $179 million to develop recombinant vaccines for the prevention of seasonal and pandemic influenza.

In late April, Novavax reported positive top-line data from a phase 2 trial for its RSV-F vaccine for women of childbearing age, causing shares to rally 18% in a single day. The stock has rallied nearly 100% over the past 12 months.

Nanoviricides' approach to MERS: Bind and dismantle
Nanoviricides is smaller than Inovio and Novavax, but it offers a radically different way of combating MERS.

Rather than develop vaccines, Nanoviricides is developing drugs that bind to viruses with virus-binding ligands in an effort to dismantle them. On May 5, Nanoviricides announced that its experimental MERS vaccine, built on that virus-binding technology, was ready for animal testing.

Nanoviricides currently has six main pipeline candidates for influenza, eye viral diseases, HIV, herpes, and dengue -- but none of these candidates have advanced to clinical trials yet. Investors should also note that unlike Inovio and Novavax, Nanoviricides is not backed by any major pharmaceutical or government collaborators.

The Foolish takeaway
Inovio, Novavax, and Nanoviricides are three companies to watch as health officials across the world struggle to understand MERS. If any of these treatments show promise, they could receive accelerated approvals due to the urgent need to treat the disease, especially across the Middle East. Of course, it's important to note that all three of these companies are clinical (or pre-clinical) stage biotechs, so they are not for the faint of heart, and investors may be better served staying on the sidelines and watching these companies.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.