Septicemic plague is one of the three main forms of plague. It is caused by Yersinia pestis, a gram-negative species of bacterium. Septicemic plague is a life-threatening infection of the blood, most commonly spread by bites from infected fleas.
Like some other forms of gram-negative sepsis, septicemic plague can cause disseminated intravascular coagulation, and is almost always fatal when untreated (the mortality rate in medieval times was 99–100 percent). However, it only occurs in a minority of cases of Yersinia infection, so that fewer than 5,000 people a year acquire the disease. It is the rarest of the three plague varieties; the other forms are bubonic and pneumonic plague.
However, septicemic plague may cause death before any symptoms occur. Also, the above symptoms are common to many human illnesses, and are not considered diagnostic of any form of plague.
Human Yersinia infections most commonly result from the bite of an infected flea or occasionally an infected mammal, but like most bacterial systemic diseases, the disease may be transmitted through an opening in the skin or by inhaling infectious droplets of moisture from sneezes or coughs. In both cases septicemic plague need not be the result, and in particular, not the initial result, but it occasionally happens that bubonic plague for example leads to infection of the blood, and septicemic plague results. If the bacteria happen to enter the bloodstream rather than the lymph or lungs, they multiply in the blood, causing bacteremia and severe sepsis. In septicemic plague, bacterial endotoxins cause disseminated intravascular coagulation (DIC), where tiny blood clots form throughout the body, commonly resulting in localised ischemic necrosis, tissue death from lack of circulation and perfusion.
DIC results in depletion of the body's clotting resources, so that it can no longer control bleeding. Consequently, the unclotted blood bleeds into the skin and other organs, leading to red or black patchy rash and to hematemesis (vomiting blood) or hemoptysis (spitting blood). The rash may cause bumps on the skin that look somewhat like insect bites, usually red, sometimes white in the center.
Untreated septicemic plague is almost always fatal. Early treatment with antibiotics reduces the mortality rate to between 4 and 15 percent. Death is almost inevitable if treatment is delayed more than about 24 hours, and some people may even die on the same day they present with the disease.
Septicemic plague is caused by horizontal and direct transmission. Horizontal transmission is the transmitting of a disease from one individual to another regardless of blood relation. Direct transmission occurs from close physical contact with individuals, through common air usage, from direct bite from a flea or an infected rodent. Most common rodents may carry the bacteria and so may Leporidae such as rabbits:
Significant carriers of the bacteria in the United States include:
The bacteria are cosmopolitan, mainly in rodents in all continents except Australia and Antarctica. The greatest frequency of human plague infections occur in Africa. The bacteria most commonly appear in rural areas and wherever there is poor sanitation, overcrowding, and high rodent populations in urban areas. Outdoor activities such as hiking, camping, or hunting where plague-infected animals may be found, increase the risk of contracting septicemic plague, and so do certain occupations such as veterinary or other animal-related work.
A doctor or veterinarian will perform a physical exam which includes asking about the medical history and possible sources of exposure. The following possible test could include:
Starting antibiotics early is a first step in treating septicemic plague in humans. One of the following antibiotics may be used:
Lymph nodes may require draining and the patient will need close monitoring.
In animals, antibiotics such as tetracyline or doxycycline can be used. Intravenous drip may be used to assist in dehydration scenarios. Flea treatment can also be used. In some cases euthanasia may be the best option for treatment and to prevent further spreading.
In 2015, Taylor Gaes, a 16-year-old in Larimer County in northern Colorado, contracted septicemic plague after being bitten by a flea that had bitten a rodent on his family's rural property. Only three people in Colorado contracted the bacteria in the previous thirty years.
Septicemic plague was the least common of the three plague varieties that occurred during the Black Death from 1348 to 1350 (the other two being bubonic plague and pneumonic plague). Like the others, septicemic plague spread from the East through trade routes on the Black Sea and down to the Mediterranean Sea.
Major port cities such as Venice and Florence were hit the hardest. The massive loss of working population in Europe following the Black Death, resulting in increased economic bargaining power of the serf labour force, was a major precipitating factor for the Peasants' Revolt of 1381.
Septicemic plague is a zoonosis, a disease that generally is acquired by humans from animals, such as rodents and carnivores. Goats, sheep and camels also may carry the bacteria. Cats rarely develop clinical signs but can be infected. Areas west of the Great Plains of North America are one region where plague-infected animals commonly occur. Plague-infested animals are found in many other countries as well, especially in developing countries where health controls are not effective.
Animals that commonly carry plague bacteria are largely rodents and Leporidae, but carnivores sometimes also become infected by their prey. Prey animals are not immune to the disease, and outbreaks of various strains of plague, such as sylvatic plague, have on occasion devastated populations of black-tailed prairie dogs and black-footed ferrets.
Plague has been active in black-tailed prairie dog populations since the 1960s. In the United States outbreaks only occur in the western States and they are devastating, with mortality rates near 100% because the animals have no immunity to the plague. Survivors are the ones that happened not to become infected and colonies that recover from a plague outbreak remain at risk.
Because black-footed ferrets prey on black-tailed prairie dogs, wild ferret populations also fall victim to sylvatic plague. An outbreak can kill nearly 100% of ferrets in a population, and surviving ferrets commonly face starvation because the prairie dogs are their main prey. Spray-and-vaccinate campaigns have aimed at preventing the spread of the plague among these animals.
Similar septicemic problems occurs in many countries across the world, especially in developing countries where spending on health systems is very low and health controls are not effective.