Two new cases of the human plague have been confirmed in New Mexico Tuesday, according to health officials. » RELATED: Possible plague case in Georgia This year, New Mexico has seen three cases of the plague, the first of which was reported in early June. >> Read more trending news All three cases required hospitalization, according to the New Mexico Department of Health. Here are seven things to know about the plague: What is it? According to Atlanta-based Centers for Disease Control and Prevention, plague is a disease caused by the bacterium Yersinia pestis that affects humans and other mammals. » RELATED: Stray cat's plague death prompts 'fever watch' What is the history of plague? Historians and scientists have recorded three major plague pandemics, according to the CDC. The first, called the Justinian Plague (after 6th century Byzantine emperor Justinian I), began in A.D. 541 in central Africa and spread to Egypt and the Mediterranean. The “Great Plague” or “Black Death” originated in China in 1334 and eventually spread to Europe, where approximately 60 percent of the population died of the disease. » RELATED: The 'Black Death': Are gerbils, not rats, to blame for plague? Lastly, the 1860s “Modern Plague,” which also began in China, spread to port cities around the world by rats on steamships, according to the CDC. In 1894, French bacteriologist Alexandre Yersin discovered the causative bacterium, Yersinia pestis. Ten million deaths resulted from the last pandemic, which eventually affected mammals in the Americas, Africa and Asia. It was during this last pandemic that scientists identified infectious flea bites as the culprit in the spread of the disease. More about the history of plague. Where in the U.S. is human plague most common? Human plague usually occurs after an outbreak in which several susceptible rodents die, infected fleas leave the dead rodents and seek blood from other hosts. These outbreaks usually occur in southwestern states, particularly in Arizona, California, Colorado and New Mexico, according to the CDC. » RELATED: Lyme disease risks could increase after mouse plague, experts warn According to the World Health Organization, an average of five to 15 cases occur annually in the U.S. Since 1900, more than 80 percent of those cases have been in the bubonic form. Worldwide, there are approximately 1,000-3,000 cases of naturally occurring plague reported every year. More about plague in the U.S. How do humans and other animals get plague? Usually, humans get plague after a bite from a rodent flea carrying the bacterium. Humans can also get plague after handling (touching or skinning) an animal (like squirrels, prairie dogs, rats or rabbits) infected with plague. According to the CDC, inhaling droplets from the cough of an infected human or mammal (sick cats, in particular) can also lead to plague. » RELATED: Rare tick-borne illness worries some medical professionals What are the types of plague and their symptoms? Bubonic plague (most common) Tender, warm and swollen nymph nodes in the groin, armpit or neck usually develop within a week after an infected flea bite. Signs and symptoms include sudden fever and chills, headache, fatigue, muscle aches. If bubonic plague is not treated, it can spread to other areas of body and lead to septicemic or pneumonic plague. Septicemic plague Occurs when bacteria multiply in the bloodstream. Signs and symptoms include fever and chills; abdominal pain; diarrhea; vomiting; extreme fatigue and light-headedness; bleeding from mouth, nose, rectum, under skin; shock; gangrene (blackening, tissue death) in fingers, toes and nose. Septicemic plague can quickly lead to organ failure. Pneumonic plague (least common) Pneumonic plague, which affects the lungs, is the most dangerous plague and is easily spread person-to-person through cough droplets. Signs and symptoms (within a few hours after infection) include bloody cough, difficulty breathing, high fever, nausea, vomiting, headache, weakness. If it is not treated quickly, pneumonic plague is almost always fatal. » RELATED: What is Lyme disease and how to avoid it How is plague treated? Immediately see a doctor if you develop symptoms of plague and have been in an area where the disease is known to occur.Your doctor will likely give you strong antibiotics (streptomycin, gentamicin or others) to combat the disease. If there are serious complications like organ failure or bleeding abnormalities, doctors will administer intravenous fluids, respiratory support and give patients oxygen. How to protect yourself, your family and your pets against plague You and your family The CDC warns against picking up or touching dead animals and letting pets sleep in the bed with you. Experts also recommend eliminating any nesting places for rodents such as sheds, garages or rock piles, brush, trash and excess firewood. Other ways to protect yourself and your family include wearing gloves if handling dead or sick animals, using an insect repellent with DEET to prevent flea bites and reporting sick or dead animals to your local health department or to law enforcement officials. » RELATED: Ticks the season: How to prevent, find and get rid of ticks this summer Pets Flea medicine should be administered regular for both dogs and cats. Keep your pet’s food in rodent-proof containers and don’t let them hunt or roam in rodent habitats. If your pet becomes ill, see a veterinarian as soon as possible. More about plague at CDC.gov.