Question

Which of the following causes plague?
A. Salmonella typhimurium
B. Trichinella spiralis
C. Yersinia pestis
D. Leishmania donovani

Answer 1

Hint: Several microorganisms are pathogenic to animals, plants and humans. They cause serious diseases and in extreme condition, they may also cause the death of the infected organism. Microorganisms such as bacteria, viruses and fungi cause the infection by transfer through contaminated food sources, through air and by transmission and contact with the infected organism.

Complete answer:
A variety of microorganisms like bacteria, virus and fungi are responsible for pathogenesis and causing death of the infected organism. These organisms are often referred to as the pathogens. A pathogen is an infectious agent or microorganism which can cause disease. A pathogenic agent can invade a host through numerous ways.

In other words, a pathogen agent may be described in terms of its ability to enter the live tissues, colonize and ability to produce toxins which can cause several changes in the host and lowering the defence mechanism of the host.

> Salmonella typhimurium is a type of bacteria which is the causative agent of typhoid fever. The bacteria infects the intestinal tract and the blood. It is a type of gram negative bacterium and infects humans. The symptoms began to appear after six to thirty days after exposure. The important symptoms are high fever, abdominal pain, headaches and mild vomiting accompanied by general weakness.

> Trichinella spiralis is a nematode parasite which is found in rodents, pigs, bears and also in humans. It causes the disease trichinosis. It is also referred to as the pork worm as the infection reaches humans due to consumption of undercooked pork. The onset of symptoms occurs from about twelve hours to two days after ingestion of undercooked meat. The parasite after entering the intestinal tract provokes an immunological response and symptoms include vomiting, sweating, and diarrhoea. The symptoms can also increase to cause muscular pain, breathing difficulty, low pulse and blood pressure.

> The causative agent of leishmaniasis or kala-azar is Leishmania donovani . It is an intracellular parasite and belongs to the genus Leishmania, a group of hemoflagellates. It is a blood parasite and infects the spleen, liver and the bone marrow. The parasite is transmitted through sand fly. The clinical symptoms include high fever with enlargement of spleen and liver and heavy skin pigmentation. If not treated properly, the disease causes death.

> Plague is caused by coccobacillus bacterium Yersinia pestis. It is a type of facultative anaerobic bacteria which infects humans through the oriental rat fleas. The disease plague has a high mortality rate and mostly spreads through rats and fleas. The flea bite transmits the bacteria into the blood system of humans. The important symptoms include high fever with decreased immune response and formation of swollen, black skin sores.

Hence, The correct answer is option (C).

Note: The pathogenic bacterium Yersinia pestis is the causative agent for different types of plague. Plague is a deadly disease which is transmitted in human beings through fleas bite, rodents or through domesticated animals like dogs and cats. The disease plague occurs in three different forms which are bubonic plague, septicemic plague and pneumonic plague. All the three types of plague are highly infectious and can cause death.