Team:Wageningen UR/Background
Background
Emerging infectious diseases
Since the beginning of the 21st century, there hasn’t been a year that was without the threat of an epidemic [1]. Outbreaks of communicable diseases have steadily increased over the last 100 years [2]. This is mainly related to globalization, climate change and the exponential increase in population density. Of these communicable diseases, only a few develop into a full-scale epidemic, but consequences can be disastrous if they are not anticipated correctly.
Especially in developing countries, infectious diseases are the major cause of death and account for more than half of all deaths in children [3] and many young adults [4]. Loss of so many potentially healthy and productive years greatly affects the economy [4] and society as a whole. Examples such as the SARS epidemic of 2002, the influenza A pandemic of 2006 or the more recent Ebola epidemic of 2014 have shown that outbreaks can happen unexpectedly and quickly. Other examples are Zika virus, a viral disease causing major outbreaks in South and Central America, and African Sleeping Sickness, which is caused by Human African Trypanosomiasis (HAT) and has been endemic in African countries for many decades. These facts underline the necessity of proper surveillance and global communication for fast responses against possible threats.
When such an epidemic emerges, the main priority is curing patients of their infection. Diagnosis is critical here, as in order to cure a person one should first know which disease the patient is infected with. Moreover, diagnosis of potential patients is important as well, as this allows for proper treatment, limitation of further spread (e.g. quarantine) and monitoring the disease impact over time [4,5]. This is especially important when there are no vaccines available.
The development of a new diagnostic test
The development of an adequate diagnostic can be challenging as many aspects are required. This is especially difficult for point-of-care diagnostic tests. These tests are used in low resource areas such as tropical areas. As a guideline, the WHO has postulated the ASSURED criteria, highlighting the most important aspects. A diagnostic test should be Affordable, Sensitive, Specific, User-friendly, Rapid and robust, Equipment-free, and Deliverable to end-users [4].
Current diagnostics: Antibody detection tests
Diagnostic tests that detect antibodies against diseases in blood samples are widely used in the field as point-of-care diagnostics. These include antibody dipsticks and agglutination tests. Both of these tests rely on the detection of antibodies against a disease in the blood of the patient and are therefore called serological tests. These antibodies will agglutinate together with the antigen present in the test, giving a visible output. These tests are easy to handle and fast but have several drawbacks. Since antibodies are present in the body even after an infection has been fended off, these tests cannot distinguish between current and past infections. Moreover, due to cross-reactivity (antibodies that can bind to multiple disease markers), false-positive results are periodically observed [6]. For example, the Card Agglutination Test (CATT) for HAT. This test is small, fast and high throughput, but it needs refrigeration, electricity and it lacks specificity. Moreover, these serological screening tests yield 99 false positives for every true positive, meaning many people are unnecessarily sent to the hospital for further investigation [7]. In dipstick tests, there is no positive control available. A negative result might mean no infection or an incorrectly working test. We learned this from dr. Philippe Büscher, HAT expert at the Institute of Tropical Medicine of Antwerp.
Mantis will be suitable for point-of-care diagnosis and targets antigens directly. The presence of a disease-causing agent, either a virus or a parasite, can now immediately be confirmed. This way, a lower rate of false positives is achieved. Also, Mantis contains a positive control whereby the functioning of the device is confirmed.
Current diagnostics: Nucleic acid tests
Alternatively, nucleic acid-based tests have been developed. Here, the DNA or RNA of the pathogen is detected. These tests are mostly used for viral diseases, and can be very sensitive and specific [5]. However, for example the Zika virus, these nucleic acid tests are only recommended to be used together with serological tests, as a negative result does not exclude being infected [8]. Moreover, these tests need specialized laboratories, expensive equipment, well-trained personnel, and are generally unavailable in healthcare facilities in third-world countries [5]. Thus, nucleic acid tests are not optimal for use in tropical areas and remote places. Mantis is point-of-care, meaning it can be used even in low resource areas.
Point-of-care diagnostic tests in iGEM
Other diagnostic tests for the detection of infectious diseases, like viruses or HAT, have been created by previous iGEM teams (for example Pasteur_Paris 2016, Shenzhen_SFLS 2016 Cork_Ireland 2015 or Aberdeen_Scotland 2014). Contrary to these tests, Mantis is modular. This means it cannot just detect one disease, it can be easily adapted to any new emerging epidemic. This makes it very suitable to be used as an initial screening method in any epidemic or pandemic situation. As said before, Mantis is point-of-care as well. This means it can be used in the field by mobile teams, having little to no need for additional equipment and training. It does not need a laboratory environment to function as is the case with most nucleic acid tests. By detecting the pathogen directly instead of through antibody detection, we rule out more false positives. Finally, we took our project a step further than just the development of the test in the lab. We created a working 3D-printed device which includes GPS and data storage for easy disease monitoring and implemented this device in our roll-out plan.
Our approach
iGEM Wageningen 2017 set out to develop a diagnostic tool with the help of experts and health care organizations around the world. Not only does our device fit in the current diagnostic picture, but it excels in modularity. By altering components, the system can be adjusted to sense different targets or change the output of the device. Using this system, we aim to create an universal and standardized point-of-care diagnostic that helps anticipate and combat rising epidemics all around the world.
We use synthetic biology to create Mantis: a point-of-care diagnostic device that can detect disease antigens in blood samples. This whole-cell system can detect the pathogen, after which it emits a fluorescent signal. Below we discuss how Mantis improves upon current diagnostics. By providing a better ASSURED diagnostic, we do not only help the population by lowering casualties and economic losses, but also enable the local community to protect themselves from infectious diseases, without being dependent on the help of foreign countries or institutes.
Applications of Mantis
By developing Mantis, the Modular Antigen-based Test for Infectious diseases, we can contribute to containing and eradicating tropical infectious diseases. Mantis can be applied in all endemic situations. We focus on the intervening role in new outbreaks of tropical infectious diseases, but Mantis can be applied in alternative situations.
Surveillance of current outbreaks
Human African Trypanosomisis (HAT) is an infectious diseases caused by the parasitic protozoan Trypanosoma brucei and is transferred via the bite of the tsetse fly [9]. It is one of many neglected tropical diseases; a disease common in (sub)tropical third world countries with a lack of funding to control the epidemics [10]. HAT is, and has been, endemic in many African countries since the beginning of the 20th century. Although great efforts have been taken to contain the disease, resulting in a decline of new cases in the last decade, it was estimated that currently still over 70 million people in the sub-Saharan region in Africa are at risk of getting the disease [11]. The symptoms start with general infection symptoms, like headaches, fever and pain, but progress further to neurological disorders like a sleeping disorder, sensory disturbances and ultimately seizures, coma and death [10].
While the WHO targets HAT for elimination by 2020, there is still a great need for the development of a new, point-of-care test for both screening and surveillance [10, 12, 13, 14]. Since HAT is a neglected tropical infectious disease with a long history, we take it as a proof-of-principle for our diagnostic device to be applied to parasitic infections.
Chikungunya, or CHIKV, is an alphavirus that is transmitted via the mosquitoes of the Aedes genus. It is or has been endemic in almost all tropical parts of the world, and is slowly spreading to colder regions [15]. The symptoms after infection include fever, photophobia, headaches, joint and muscle pain and skin rash [16]. As many current infectious disease outbreaks involve viruses [1] it is important that Mantis can detect these as well. For this, we are using chikungunya as proof-of-principle.
Alternative applications
Apart from a point-of-care screening test during epidemic outbreaks of infectious diseases, Mantis can in principle be applied in other situations. We explored several of them.
Veterinary
As described before, HAT causes many deaths in Africa. This is caused by Trypanosoma brucei gambiense and T. b. rhodesiense. However, related parasite species like T. b. brucei and T. congolense can infect livestock. This causes Animal African Trypanosomiasis (AAT) that results in major economic losses in the affected countries [9]. Our test can be used for veterinary purposes as well. However, since the social and economic impact will be less significant, we focussed on human testing.
Vector control
HAT is transmitted by the tsetse fly. In order to reduce the spread of the disease, surveillance of vector populations can be valuable. Moreover, the other form of HAT, caused by Trypanosoma brucei rhodesiense, is difficult to eliminate not only by the lack of available screening kits, but even more by the vast amount of animal reservoirs which serve as an intermediate for disease transmission. A key part to control T. b. rhodesiense HAT is the monitoring of the domestic reservoirs infected by the parasite, as well as reduction of the tsetse fly population [17]. For viral diseases, like Zika and chikungunya, vector control is also a very important factor, since these diseases are transmitted by mosquitoes. Since the Mantis device is equipped with GPS data storage, it would be suitable for vector monitoring and spread. However, we found out that a modular tool like Mantis is not the top priority within vector control, hence we decided to focus our project on human screening. You can read why on our Integrated Human Practices page.
There are thus several opportunities for our modular test to be used in the field. For our integrated human practices, we emphasized on applying our device for screening during new disease outbreaks. How we got to this idea, you can read in our timeline. In the roll-out plan, you can read how our device will be implemented in the situation of an epidemic and thereafter.
References
- World Health Organisation, “Disease outbreaks by year“ http://www.who.int/csr/don/archive/year/en/ retrieved on 23 oct 2017
- Smith, Katherine F., et al. "Global rise in human infectious disease outbreaks." Journal of the Royal Society Interface 11.101 (2014): 20140950.
- Kent, Mary Mederios, and Sandra Yin. "Controlling infectious diseases." Population Bulletin 61.2 (2006): 1-20.
- World Health Organization. "World Health Organization outbreak communication planning guide." (2008).
- Mabey, David, et al. "Tropical infectious diseases: diagnostics for the developing world." Nature Reviews Microbiology 2.3 (2004): 231-240.
- Lemass, Darragh, Richard O'Kennedy, and Gregor S. Kijanka. "Referencing cross-reactivity of detection antibodies for protein array experiments." F1000Research 5 (2016).
- Büscher, P., Cecchi, G., Jamonneau, V., & Priotto, G. (2017). Human African trypanosomiasis. The Lancet.
- Centers For Disease Control and Prevention (CDC), “Diagnostic Tests for Zika Virus” https://www.cdc.gov/zika/hc-providers/types-of-tests.html. Retrieved on 25 October 2017
- Alsan, Marcella. "The effect of the tsetse fly on African development." The American Economic Review 105.1 (2014): 382-410.
- World Health Organization. “WHO | Human African Trypanosomiasis.” WHO. World Health Organization, 2016.
- Simarro, Pere P., et al. "Estimating and mapping the population at risk of sleeping sickness." PLoS neglected tropical diseases 6.10 (2012): e1859.
- Chappuis, François, et al. "Options for field diagnosis of human African trypanosomiasis." Clinical microbiology reviews 18.1 (2005): 133-146.
- Büscher, Philippe, and Stijn Deborggraeve. "How can molecular diagnostics contribute to the elimination of human African trypanosomiasis?." Expert review of molecular diagnostics 15.5 (2015): 607-615.
- Aksoy, Serap, et al. "Human African trypanosomiasis control: Achievements and challenges." PLoS neglected tropical diseases 11.4 (2017): e0005454.
- Morin, Cory W., Andrew C. Comrie, and Kacey Ernst. "Climate and dengue transmission: evidence and implications." Environmental health perspectives 121.11-12 (2013): 1264.
- Weaver, Scott C., and Marc Lecuit. "Chikungunya virus and the global spread of a mosquito-borne disease." New England Journal of Medicine 372.13 (2015): 1231-1239.
- Rock, Kat S., et al. "Quantitative evaluation of the strategy to eliminate human African trypanosomiasis in the Democratic Republic of Congo." Parasites & vectors 8.1 (2015): 532.
