Tosari Virus Fever

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About This Module 

Topics: Human health, epidemiology, pathogens (viruses), modes of transmission, re-emerging disease

Grade levels: 9-12


Students investigate a fictional outbreak of Tosari Virus Fever in Bangladesh. They work to identify the disease transmission method in an effort to control and contain what looks to be a re-emerging disease outbreak.

Learning Objectives 

To better understand the ways infectious disease can be transmitted, students should be able to:

  • Compare and contrast different disease transmission methods.
  • Identify ways to avoid infection by pathogens that use direct and indirect transmission methods.
  • Describe how viruses cause disease.
  • Explain how knowing the mode of transmission impacts epidemiology processes and the prevention and control of disease.
  • Apply knowledge of epidemiological methods and disease transmission to solving a disease outbreak.
  • Explain how a virus may change to infect new different hosts.

Next Generation Science Standards

Standards Aligned to PBL Modules

Important Note! 

Do not have your students watch the video “Hunt for the Next Plague” if you are using this module. This problem-based learning module incorporates into the scenario transmission methods and vectors from a Nipah virus outbreak. While obviously completely accurate for scientific content (based on an actual outbreak), your students will recognize the viral “story” and know how the virus is being transmitted.

After students work through the problem, you can show the video for its excellent example of applying epidemiological methods to a disease outbreak. It is also an excellent way to showcase scientists at work solving real problems. The scientists in the video have varied careers, and they have worked for years studying outbreaks in different locations around the world. They solve the Nipah outbreak and also come up with novel ways to prevent future outbreaks from the same source.

Scenario (with possible answers) 
Female scientist using microscope to analyze samples.
Analyzing microscopic samples. Image: CDC

“Have you read these reports? This looks pretty bad.”  You and your colleague, Maria, just got some information about a new assignment.  It looks like you are both on your way to Bangladesh to investigate the emergence of a disease outbreak occurring there.

In your work with the National Institutes of Health (NIH) you have investigated many different diseases and outbreaks. Each one is a challenge, but this one seems to be particularly disturbing.

You have just skimmed the first few paragraphs, and what you read is chilling.

“You know what this looks like, right? Are you thinking the same thing? Tosari?”

Maria looks pretty grim. “Yes, I thought the same thing.  But, how? We haven’t had an outbreak of Tosari in years and that was 2,100 miles from Bangladesh! How is it just popping up over 2,100 miles away? And in humans right off the bat?”

“Ok,” you say to Maria, “Let’s go through this info and then we can start to plan our next moves. It looks like we can do a lot of prep work before we even get there. The field investigators with the Bangladesh Infectious Disease Unit in Dhaka have sent a few patient interviews.  Maybe we can sort things out and get some clues to how this virus—if it’s even Tosari—is being spread this time. ”


Map showing the location of Bangladesh
Location of Bangladesh. Bordered by India and Myanmar in South Asia.

After reading the briefing information and data, you look at Maria and hope the preliminary reports are wrong. The reports—according to the symptoms— seem to indicate that an outbreak of Tosari Virus Fever is occurring in Bangladesh. You know the country is a hotbed of viral outbreaks. The environment, recurrent severe weather events, poverty, and social and cultural practices play important roles in fostering the spread of disease, but they’ve never had Tosari before.

Tosari Fever is a re-emerging disease that seems likely to be a major infectious disease given its rapid increase in the number of cases elsewhere in the world. If this is Tosari, you both know that time is a critical factor in containing the outbreak, but without known transmission methods or an effective vaccine, there is little hope of preventing or containing the disease quickly.

Of particular concern is the high mortality, or death rate, for this outbreak. Tosari Fever is an incurable, deadly disease. Victims become ill with a high fever and 48 hours later, they fall into a coma. Within one week, 7 out of 10 have died. The last Tosari outbreak, in Indonesia over 5 years ago, did not have this high mortality rate. What is happening in Bangladesh and how did the virus get there?

Investigators with the Bangladesh Infectious Disease Unit have already sent you some patient data and interviews so that your team can identify clues that may lead to the transmission method. Somewhere, embedded in the patient interviews are the clues you need in order to identify the transmission method of the Tosari virus in Bangladesh. You know that identifying the transmission method is key to prevention and containment. You also know that a disease can be transmitted in more than one way; identifying each transmission method is important.

The outbreak seems to be occurring in several locations. Cases have been reported in Faridpur, Tangail, Baliakandi, and other small villages and towns on the Padma and Chandana Rivers.  Cases have also been reported in the capital city of Dhaka, but those have involved family members who have come to take care of relatives who have been brought to the Dhaka hospital.

Given the ease and frequency of travel in today’s world, health officials at NIH, the Centers for Disease Control and Prevention (CDC), and the World Health Organization (WHO) are concerned that the deadly virus may spread to other countries.

Bangladesh is about as large as the state of Iowa. It is one of the poorest yet densely populated countries in the world. It has over 700 rivers and the world’s largest delta, the Bengal Delta, just to its south. The country often floods in the monsoon season which lasts from June to October. Natural disasters, such as floods, cyclones, and tornadoes occur every year. Severe floods are not uncommon.

You love your work and the travel to exotic locations. You have visited Bangladesh before; the people are wonderful and the country is beautiful! Hopefully, you can quickly resolve this outbreak and save lives.

Your Task

Review the Tosari Virus Fever information and patient interviews for clues to figure out how this disease may be transmitted. Knowing how the disease is transmitted will help identify prevention and control strategies and may possibly allow the outbreak to be controlled quickly.  You know you have to find answers quickly and accurately for your briefing to your colleagues at the NIH and CDC and for public health officials in Bangladesh anxiously awaiting some guidance.

   Use the following Guiding Questions to help you determine key information about the Tosari virus and to help you prepare your report to the NIH and CDC. Your report should include information about the virus, most likely transmission methods, and prevention and control measures that could limit and/or stop the outbreak from spreading. Be able to support your recommendations with evidence and information on viral diseases and transmission methods.

Guiding Questions:

1) What are the possible transmission methods for Tosari Virus Fever given the information in the description and the patient information and interviews? After reading the patient interviews, make a list of every possible transmission method based on patient information provided.

Possible student answers:

  • person-to-person
  • poisonous palm tree sap
  • infected tree sap
  • infectious disease at the market
  • insect or other vector in the jungle carrying disease
  • water borne

 2) Of course, no official decision will be made until scientific evidence from laboratory testing is available.  However, you can now narrow the transmission methods you listed to the most likely methods. Give your reasons for eliminating any transmission method.

  • person-to-person—possible. Infected people in the villages were around other people who then got sick. Other family members got sick after one member was sick.
  • poisonous tree sap—Unlikely. People have been drinking the tree sap for a long time and never got sick. Other people drank this tree sap and didn’t get sick.
  • infected tree sap—possible. If the tree sap was infected with a pathogen, then people who drank the tree sap may become infected. But, person-to-person would also have to occur if people who did not drink infected tree sap also got sick.
  • infectious disease at the market—Unlikely. People in the village who never went to the market at all got sick. People in the villages got sick first.
  • insect or other vector in the jungle carrying disease—possible. The jungle has a lot of different vectors. But, the vectors would have been there for a long time and people wourld have been getting sick with Tosari Virus Fever in other outbreaks. However, could something else have happened that would have changed this?
  • water borne—Unlikely. Although some of the victims of this disease worked near water, people in the capital who visited family members in the hospital also got sick. (All cases in Dhaka started in the hospital.)

Therefore, the most likely transmission methods are:

  • person-to-person
  • infected tree sap
  • insect or other vector in the jungle carrying disease

3) How could each of the most likely transmission methods be tested to find out if it could be spreading the disease in Bangladesh?   

person-to-person—test patients to find out if the pathogen is present.

infected tree sap—test the tree sap for the presence of the pathogen

insect or other vector in the jungle carrying disease—test a variety of vectors linked to the tree sap for the presence of the pathogen

4) Which transmission method is your top choice?  You may list more than one if the patient interviews suggest more than one method, but only if you think they are equally responsible for the spread of infection. Defend your choice.

infected tree sap—Two patient interviews report a link to the date palm sap. It is likely that the sap is contaminated with Tosari virus, but how did it get there?

vector associated with the tree sap—The fruit bats come to drink the tree sap and could contaminate the sap with a pathogen.

person-to-person—People not associated with the villages, the jungle, or tree sap are still getting sick. Although this has never happened with Tosari, viruses can mutate and have the capability of infecting new hosts.

5) There are more clues in patient interviews than just symptoms and locations. Did you notice anything that a few of the patients have in common?  Could this possibly be important to figuring out how to stop the spread of this disease?

Two patients report a link to the date palm sap.

One patient reports that bats are a nuisance at night because they fly at the date tree sap gatherers and try to bite them. Another patient harvests the date palm sap from trees right outside his village.

5) Laboratory testing can take weeks depending on the type of test. Public health officials want to begin prevention, control, and containment measures as soon as possible so new cases, illness, and deaths are kept to a minimum. Often, prevention and control measures are instituted before test results are obtained. Based on the transmission methods, what prevention and control strategies will you and your team suggest to public health officials?

In this outbreak, Tosari Virus Fever is most likely spread by a vector possibly infecting tree sap. Villagers should cover the containers used to collect the tree sap so that a vector cannot contaminate the sap.

People should avoid contact with bats who are vectors of Tosari Virus Fever.

Additional Notes 


The scenario has two NIH scientists saying that although a Tosari outbreak occurred in Indonesia years ago, it has never occurred in Bangladesh. They question whether the Bangladesh outbreak could be Tosari because Tosari was not known to infect people. And how did it get 3,000 miles from any known Tosari reservoir? Your students may need some further explanation of how a virus is capable of both.

The virus was always in both places. Environmental factors and demographics played a role in the virus jumping from the fruit bat to humans in Bangladesh. The people moved closer to the rain forest where the bats lived and started to collect the date palm sap from date palm trees in the forest and very near the village. The villagers collected the sap to eat and to sell; the bats had come to eat the juice that leaked from the trees where the villagers had sliced into the trees and installed jars to collect the sap. The bats ate the sap and contaminated the jars and sap with Tosari-infected saliva and urine. The people drank the sap from the jars and got sick.

The virus was in both places—Indonesia and Bangladesh—but there were different strains of the virus. The Bangladesh virus was more virulent and more deadly and had jumped from bats to humans and more disturbingly then jumped from human to human.

Sample Rubric 

Information about constructing and implementing rubrics for problem-based learning strategies can be found in Developing Rubrics in the Teacher Professional Development section.


Invite your county or district public health officer or an epidemiologist from a local university (or both) to talk to your classes about how public health is monitored in your area.

► Have your students complete another problem-based learning module that focuses on an outbreak. The Outbreak!  module uses an interrupted case study approach that allows your students to work an outbreak step-by-step, receiving reports and alerts throughout their work.

► Watch the Frontline PBS documentary “Outbreak” which details the 2014-2015 Ebola epidemic in West Africa. The video describes how it may have started, what caused it to spread through several West African countries, and how mishandling of key epidemiological practices resulted in thousands of deaths. It also details the epidemiologic investigative process used in the outbreak.

NOTE: Be sure to watch this video before showing it to your class.  At times, this video is difficult to watch. It shows people who have contracted Ebola and it presents desperate conditions in medical camps built to deal with Ebola cases. It is an excellent video that highlights the different factors, including social, cultural, political, and economic issues that influence the efforts of dedicated medical professional in trying to stop the epidemic, but it may not be suitable for all classes.

Access the Frontline Outbreak! video at You can also access the teacher and student Study Guide from this site.

► For a more personal perspective on disease investigations, have your students watch the NOVA 14:40 minute “Zika: The Untold Story”. This interesting and well-narrated video describes the discovery of the Zika virus in 1947 in Uganda by Alexander Haddock and the subsequent study of the virus by his grandson, Andrew Haddock. The video describes Zika’s recent re-emergence as a dangerous viral infection. Access the video at

Additional Resources 

Additional resources about emerging and re-emerging diseases can be found:

in the Key Resources section in the Pandem Disease Center at

in the Tosari module background materials (Internet Resources for Emerging and Re-emerging Diseases) at