Sample Student Case Study

 

Mike, a 35 year-old man came to his primary care doctor in upstate New York presenting with symptoms of weakness and fatigue. Mike continues to say that he had a headache, fever, and chills a day or two ago, and has had less energy since. The physician wisely asks for recent travel activity and Mike describes the quick trip that he and his wife took to her parent’s home in India about 2 weeks ago. The trip was planned last minute following the death of his wife’s cousin. The only up side of the trip was the delicious chicken that was prepared by his in-laws, whom own a chicken farm. His wife does not have similar symptoms. Upon hearing the story about the chicken, the doctor’s eyes light up, he prescribes amoxicillin, an antibacterial medication, and takes a blood and urine sample to be sure. Later that night the doctor reviews the blood and urine and the only abnormality he sees is extremely high levels of hemoglobin in the urine, he assumes it to be a mistake and takes no action. The next day, Mike returns with a fever, chills, and jaundice in his eyes. Identical to the symptoms he had 2-3 days ago but more intense.

 

1. Based on the original prescription that the doctor wrote, what did he suspect was the disease?

 

The doctor believed that Mike had Typhoid fever, caused by Salmonella enterica bacteria that can be found in poultry. The doctor prescribed an antibacterial to fight this infection, but it looks like he made the wrong diagnosis…

 

1. When Mike returns to the doctor, another blood test is taken and analyzed quickly to reveal a multiple protozoan aplicomplexans in the blood smear. What is the new diagnosis and what is the causative agent based on the new lab results?

 

The new diagnosis is Malaria. Malaria is caused by Plasmodium. There are four species of Plasmodium that can cause malaria. In India, the most prominent is P. vivax, followed by P. falciparum, the causative agent of most severe malaria.

 

1. How did Mike get this infectious disease? And what about this diseases life cycle and pathogenesis caused the cyclic symptoms?

 

Mike got Malaria from a bite from an infected female Anopheles mosquito. Upon biting Mike, the mosquito injected sporozoites of Plasmodium into his blood. The sporozoites travel to the liver where they undergo schizogony (multiple mitoses to create up to 64 nuclei) over a 1-2 week incubation period. These cells then rupture and release many merozoites (one nuclei) into the blood. Merozoites penetrate erythrocytes and undergo schizogony again. Further incubation inside of the erythrocytes takes 2-3 days before rupturing and causing symptoms, thus explaining the cyclic symptoms. The symptoms are due to the immune response to the malaria parasites, erythrocyte debris, and toxins. While the Plasmodium are inside erythrocytes they are not detected by the immune system because RBCs do not have MHC complexes and cannot present antigens.  In addition, lab detection can also be avoided due to the cyclic Plasmodium life cycle.

 

1. During the first visit to the doctor, Mike showed signs of the infectious disease. Mike’s previous symptoms of fever and chills, his current symptoms weakness and fatigue, followed his lab results should have led to the diagnosis in part B. What do the initial lab results and symptoms reveal about the infectious disease?

 

The initial lab results indicated extremely elevated levels of hemoglobin. This lab result is characteristic of lysing erythrocytes. During the Plasmodium life cycle, erythrocytes lyse simultaneously, and hemoglobin is excreted in the urine. This loss of hemoglobin leads to the symptoms of weakness and fatigue because oxygen transport in the blood is diminished. After erythrocyte lysing, the infectious merozoites the find new erythrocytes to invade and thus can avoid detection if sample is collected between the 2-3 day cyclic cycle.

 

1. Mike’s wife contacted the same infectious pathogen, but she does not have any symptoms of the disease and never will. How is this possible?

 

Mike’s wife has sickle cell trait. In India, sickle cell disease is prominent 10-20%, so sickle cell trait is also prominent. Individuals with one sickle cell gene produces abnormally shaped hemoglobin (type S) that cause sickle shaped erythrocytes. This change in shape allows the erythrocytes to resist penetration from the Plasmodium pathogen, thus increasing the individual’s resistance to malaria.

 

1. (bonus) The doctor prescribes an antimalarial drug chloroquine to combat Mike’s P. vivax malaria, but it does not treat Mike’s malaria. Very annoyed at his current doctor, Mike seeks out a doctor in Canada that prescribes him another medication and cures his symptoms with one dose. Why did chloroquine not work to treat Mike’s malaria? What did the Canadian doctor prescribe that worked so well? (hint: the American doctor is not allowed to prescribe this medication)

 

Although chloroquine is the treatment of choice for P. vivax malaria, there is increasing resistance to this medication throughout parts of India and Asia. After switching doctor’s Mike was prescribed artemisinin, a traditional Chinese herbal treatment that is relatively new to the Western world. The drug is given in combination with other antimalarial drugs to avoid Plasmodium acquiring resistance to this effective medication. Unfortunately, artemisinin is not approved for use in the US or UK.