| Case A | Case B |
Background: What is malaria? Malaria is a blood-borne pathogenic disease caused by protozoans of the genus Plasmodium spp., which is an internal parasite that preys on human red blood cells. It is common in tropical and subtropical regions and transmitted to humans via infected bites from Anopheles spp. mosquitoes. Approximately 500 million infections occur each year, and more than one million die from the parasite, many of whom are young children.
What causes malaria? Malaria is thought to have originated in tropical African and spread with ancestral hominids as they migrating across the globe, affecting populations from the Mediterranean to eastern China and all parts in between. Before the advent of modern science the causes of most pathogenic diseases were unknown, even if the symptoms were common. Malaria was often observed in individuals who lived and worked in or near marshy, estuarine habitats where mosquitoes breed; however, people did not associate the disease with insect bites, rather connecting it with the bad fumes that often arise from swamps as pockets of methane created by rotting vegetation. The name “malaria” is in fact derived from the Latin words for “bad (mala)” and “air (aria)” referring to these fumes, which ancients thought caused the disease.
There are four species of malaria-causing Plasmodium: P. falciparum, P. malariae, P. vivax, and P. ovale. Each of these species causes an individual variation of malaria.
| P. malariae | P. vivax | P. ovale | P. falciparum | |
|---|---|---|---|---|
| Disease variant | “Benign malaria” | “Tertiary malaria” | “Tertiary malaria” | “Cerebral malaria” |
| Endemic area | Southern Europe, Middle East, North Africa | Asia, Africa, & South America | West Africa & southeast Asia | Sub-Saharan Africa |
| Malignancy level | Low | Medium | Medium | Extreme |
| Mortality rate | None | Low | Low | High |
| Fever cycle | Every 4 days “quartan fever” | Every 3 days “tertiary fever” | Every 3 days “tertiary fever” | No cycle |
| Treatment | ? | Chloroquine | Chloroquine or Primaquine | Artemisinin |
| Recurrence | Infrequent | Possible | Possible | Often deadly |
What are the symptoms of malaria? Malaria is frequently mistaken for other, more pedestrian disorders, especially in areas where it is not endemic such as the United States and many European nations. Many of the symptoms are similar to those of the common flu and include: fever, chills, headache, general weakness, nausea, vomiting, muscle pain, cough, and/or diarrhea. Malaria is diagnosed by microscopic examination of blood, looking for the Plasmodium organisms in blood cells. Molecular biology techniques, such as PCR, and be used to make a more definitive diagnosis. Nested PCR may be used in a laboratory diagnosis. First a general primer set that should react with all Plasmodium species is used, which will amplify an approximately 1100 bp fragment. Then this product is used as a target for a second round of PCR with species-specific primers. The products expected with the specific primers are 205 bp for P. falciparum, 120 bp for P. vivax, 800 bp for P. ovale, and 144 bp for P. malariae.
What drugs are used to treat malaria? As with most diseases, the sooner malaria is treated, the better. The Centers for Disease Control recommend that treatment begins no later than 24 hours after the first symptoms occur. There are a variety of drugs available to treat malaria, the most common of which are synthetic, but chemically based on quinine, which is derived from the bark of the Cinchona tree (and commonly found in tonic water). This group of drugs includes: quinine, chloroquine, mefloquine, and primaquine. Other drugs used in the treatment of malaria are a combination of atovaquone and proguanil, a combination of sulfadoxine and pyrimethamine, the antibiotic doxycycline, and Artemisinin. Artemisinin is a lactone product of the Sweet Wormwood plant and has been used by Chinese physicians since 340 A.D.
Where may one contract malaria? One of the four species of Plasmodium that causes malaria can be found in most tropical and subtropical countries throughout the Old and New Worlds. Note that some areas that have historically been endemic areas (such as southern Europe) now pose very low infection risks due to eradication programs.
Case A. Sergio Román was glad to be surrounded by his family during the holidays. This would be the first Christmas without his older sister, Milagros, who died after contracting malaria during a missionary visit to Columbia. She was diagnosed when she returned to Puerto Rico with a high fever that came and went every few days. Milagros took the drugs they prescribed and seemed to recover, but a month later the fevers returned, and this time she did not recover. Sergio was frustrated because he did not understand why the drugs did not work for Milagros. Other members of the mission group, including Sergio’s younger sister, Rosario, had also become infected but recovered fully after the drug treatments. Both were treated with the same dosage of chloroquine. It did not seem fair that a disease that was supposedly eradicated from Puerto Rico many years ago should take such a toll on Sergio’s family. Milagros and her family had agreed to allow her blood samples to be used for research into drug resistant malaria.
Procedure: To determine which species of Plasmodium infected the two sisters, perform a nested PCR by first amplifying DNA isolated from their blood with a general Plasmodium primer set. Then use a second round of PCR, amplifying the first PCR product using species-specific primers.
Bioinformatics: SIngle nucleotide polymorphisms (SNPs) in the multidrug resistance gene pfmdr-1 have been associated with resistance to the drug treatments used for Milagros. Test DNA samples from Milagros and Rosario by using PCR with primers that will amplify regions containing SNPs. Compare the sequences of the PCR products by clicking on the fragments one at at time, exporting the sequences of corresponding bands to the Export field, and using MEGA to align them.
- Which species of Plasmodium infected the two sisters?
- Does the Plasmodium DNA isolated from Milagros appear to contain any SNPs that might be associated with drug resistance?
- Is there a different treatment that may have worked better?
- How would you explain why Rosario was able to recover from malaria but Milagros was not?
Case B. Jennie could not wait to tell her best friend the news. “You’re kidding me! Your dad actually bought you that ‘round-the-world’ ticket you’ve been asking for every birthday since you turned 18?” Synove looked at her best friend incredulously and continued, “I just can’t believe it!”
“Yup.” Jennie answered, looking a little smug. But then her face brightened as she smiled, telling Synove, “But, he said I couldn’t go alone. So he bought TWO tickets and told me to pick a friend to go with me! That’s you!”
“No way!” Synove shouted. “Where are we going to go?”
“Well, I thought we’d start off heading to Europe first just to get acclimated to traveling on our own. Maybe start in Paris and bike to southern Spain. Then cross the Straits of Gibraltar to Morocco and head down west Africa. Then we hop a flight Victoria Falls in Zimbabwe; safari in Botswana and Namibia; Cape Town; and up the east coast for a break in Dar es Salaam. From there we can fly to India and bum around a bit before heading to Thailand and Cambodia. Then we visit my extended family in Taiwan before catching a flight to Japan and from there back to Seattle. What do you think?” Jennie asked.
“Wow. Sounds great! Do we have to get any shots before we go?”
“I’m pretty sure, but I’ll ask my mom tonight.” Jennie said.
“Of course! A doctor would know…”
“Well girls, you’re going to need lots of shots before you go on this world tour of yours.” said Jennie’s mother. You’ll need Yellow Fever, Hepatitis A and B, Typhoid, Rabies, and Meningococcal. Jennie I know you’ve had it, but Synove, do you know if you were vaccinated for Polio as a child? If not, you’ll need that. For India, Thailand, and Cambodia you’ll probably need to get Japanese encephalitis too if you’re going to be in rural areas. You should probably get Dengue Fever immunizations too, just to be on the safe side. Good thing you’ve got about eight months before you leave. All these shots are going to take a while.”
“Mom, what about malaria? Do we need to worry about that?”
About a week after returning from their trip, Jennie began to feel ill. She was feverish, felt weak, had a headache, and just ached all over. Both she and Synove thought it was just the flu. But one afternoon, Synove couldn’t wake Jennie from a nap she was taking between classes and called an ambulance. Based on Jennie’s recent travels and her symptoms, the physician at the hospital orders a blood analysis, which revealed evidence of Plasmodium.
Procedure: To confirm that Jennie is infected with Plasmodium, perform a nested PCR by first amplifying DNA isolated from her blood with a general Plasmodium primer set. Then use a second round of PCR, amplifying the first PCR product using species-specific primers.
- Which species of Plasmodium infected Jennie?
- What treatment(s) would you recommend based on the diagnosis?
- What other advice would you have for Jennie? What is her prognosis?
- Is there anything the girls could have done to prevent infection?