We’ve heard that word a lot the past couple years.
Perhaps you’ve also heard the term “emerging infection.” According to the CDC, these are diseases “whose incidence in humans has increased in the past two decades or threaten to increase in the near future.” SARS-Cov-2, the virus that causes COVID-19, is considered an emerging infection, along with HIV, Influenza, Zika, etc. The ones I will be discussing in this article are some of the rarer ones, but in my opinion, the most interesting.
Ebola viruses belong to a group of viruses called filoviridae. Filoviruses form very long, filamentous shapes; the Ebolavirus specifically looks like a shepherd’s crook. Viral particles contain one molecule of single-stranded negative-sense RNA enveloped in a lipid membrane. New viral particles bud from the surface of the host cell.
There are five types of Ebola each named after where they originated: Zaire, Sudan, Bundibugyo, Tai Forest, and Reston. The first three subtypes are associated with the largest outbreaks in Africa.
Ebola viruses are known to cause hemorrhagic fever in humans. Symptoms include fever, headache, vomiting, diarrhea, and in severe cases, damage to blood vessels/hemorrhage. Mortality rates range from 25 to 90 percent, with an average of 50 percent. Death is normally caused by shock due to fluid loss rather than blood loss.
Ebola is a zoonotic virus, meaning it is transmitted from animals to humans. Ebola’s reservoir is particularly found in fruit bats. In West Africa, it is very common for people to kill and eat bats as bushmeat. Children also often play in the hollows of trees where these animals reside, making transmission via blood and feces extremely common.
There are no vaccines or treatments approved for the treatment of Ebola, however experimental ones are being tested. Ebola is considered a Class A bioterrorism agent; because it is so lethal, it must be handled in a Biosafety Level 4 laboratory, which there are very few of in the world.
Like Ebola, Nipah is a zoonotic virus; its route of transmission is from horses to bats to people, as well as from pigs to people. It is not a filovirus, rather a paramyxovirus, meaning that its shape is more circular, as they are enveloped particles.
Paramyxoviruses are known to cause respiratory infections, so Nipah patients often experience sore throat, respiratory distress, and fever. What’s even more interesting is that there are neurological manifestations of the disease as well, including encephalitis, or inflammation of the brain. This can cause seizures and, in severe cases, a coma. Most people who survive encephalitis have a full recovery, but their behavior and personalities are often altered. The case fatality rate for this disease is extremely high--around 40 percent to 75 percent.
This virus has been seen before in Malaysia, Bangladesh, and India. In these countries specifically, palm oil is often used; however, bats also inhabit these trees, greatly increasing the transmission of the Nipah virus.
There is currently no vaccine or cure, however there is current research going on to develop a vaccine before Nipah potentially ever gets out of hand.
Unlike Ebola and Nipah, Tularemia is caused by a bacterium, not a virus. This bacterium is Francisella tularensis, one of the most infectious agents known. If this bacteria is inhaled, it can cause severe respiratory and systemic disease that has a mortality rate of 30 percent if not treated with antibiotics.
This bacterium is naturally found in rabbits and hares, so this is often called rabbit fever. People can also become infected by flea/tick bites. Tularemia is not known to spread from one person to another.
This makes the transmission of Tularemia not very high, but what makes it scary is that it is classified as one of the highest risk bioterrorism agents. Research for this has already been conducted in Japan, the former Soviet Union, and the United States. This bacterium has been used for bioterrorism research because since it is already so commonly found in nature, it is easy to harvest and grow in a lab, and it is easily disseminated in aerosol form.
Like Ebola and Nipah, there’s research currently underway to develop a vaccine, but nothing has been released yet.
Chikungunya is a virus transmitted to humans by mosquitoes. It’s name is derived from the Makonde language which means contorted or bent, referring to the stooped appearance of its victims who suffer from severe joint pain.
Chikungunya is classified as an alphavirus belonging to the Togaviridae family. It’s an RNA virus surrounded by a lipid envelope; the viral particles are small and spherical.
Symptomatically, it’s similar to Dengue and other mosquito-transmitted viruses. Chikungunya is rarely a fatal disease, but the severe joint pain is often debilitating. It typically lasts a few days, but has been seen to last several weeks or even months.
The types of mosquitoes that carry this virus are prevalent in some areas of the United States, particularly Florida and Texas. Widespread transmission is unlikely, but local transmission in these areas is a possibility. There is no antiviral treatment for this disease, only symptom control. There is also not a vaccine yet, so the best preventative measures are insect repellants.
Diagnostic testing (RT-PCR) is currently being developed.