Death knell to dengue

• Can the Photodynamic Larvicide end dengue? 

• When the larvae feed on it, it is not a toxic substance, but it becomes toxic the moment it is exposed to sunlight.

As many as 100,212 Sri Lankans were victimized by the dengue menace last year, according to statistics provided by the Ministry of Health’s Epidemiology Unit. The number certainly has risen since 2018 amid various approaches taken to eliminate the breeding of Aedes Mosquitoes. Recently, a German Scientist visited the island to introduce a cheaper, non-toxic and biodegradable compound, which has proved to work on local mosquito larvae.  

Prof. Donat Peter Häder, a German botanist retired from the Department of Biology at the University of Erlangen-Nürnberg was accompanied by Prof. Lakshman Andradi, attached to the Department of Chemical and Biomolecular Engineering at North Carolina State University, USA. 

Then we went to Egypt and got involved with the largest pharmaceutical company near Cairo. We then started producing the material at a factory and used it in Burkina Faso. That was successful, and the other collaboration we had was in Brazil. We have been using it there for the past 20 years for malaria, dengue, Zika, and it also works against fish parasites - basically anything in the water.

Once reading through the chemistry of the compound, Prof. Andradi has invited his German colleague to test it on local larvae, knowing that dengue is a persistent menace. The trial compound was made at the Industrial Training Institute and was tested at the University of Kelaniya, Medical Faculty.

“Dengue is spreading in over 140 countries in tropics, subtropics and even Europe and colder countries,” cautioned Prof. Häder in an interview with the . “Close to half the population on this planet is liable to be infected by dengue as per WHO statistics. Hospitalization is about 250,000 per year and 2.5 per cent of them die. Malaria kills about a million people every year. At the university, we had a dark control room and one with light. The experiment worked under the light. For this trial, the compound was prepared using spinach leaves, but we needed to shift to another plant later. We can use any green plant, but the ideal thing would be to use something we throw away. Something not edible but available in large supply,” he added.   

This idea bore fruition at the University of Erlangen-Nürnberg. I first started with PhD and Master students to test the compound under lab conditions   

Prof. Donat Peter Häder      

Prof. Häder said this idea bore fruition at the University of Erlangen-Nürnberg. “I first started with PhD and Master students to test the compound under lab conditions.

Then we went to Egypt and got involved with the largest pharmaceutical company near Cairo. We then started producing the material at a factory and used it in Burkina Faso. That was successful, and the other collaboration we had was in Brazil. We have been using it there for the past 20 years for malaria, dengue, Zika, and it also works against fish parasites - basically anything in the water.  

At present, if a dengue case is found, an organophosphate pesticide usually mixed with kerosene or gasoline is used     

Prof. Lakshman Andradi

The main point is that it’s derived from chlorophyll, so we can use any plant material which could either be waste or any other plant which is not used commercially. Therefore the source could be very cheap and it is non-toxic as well. It’s extremely sensitive and could be used in low concentrations, on the order of 8.8 micrograms per ml,” he said.

The technique followed is similar to that used to kill cancer cells. “When you have cancer, a patient is injected with a substance which is taken up by cancer cells. It is then irradiated by laser rays or sunlight that very effectively kills cancer cells. Here the mosquito larvae take up the chlorophyll. When observed under a microscope one can see bright red fluorescence inside their intestines. We work together with a famous medical institute in Germany where we developed the idea of how to kill the mosquitoes. The cells lining the intestines are being disrupted, and that’s how they die. What you do is you get the material and spray it in an infected area. Mosquitoes don’t live in large lakes but small puddles, or inside a hole in a tree. So you spray in the evening and when the sun rises the next morning the mosquitoes are killed,” he explained.

Stressing on its benefits, Prof. Andradi said that at present, if a dengue case is found, an organophosphate pesticide usually mixed with kerosene or gasoline is used. 

This could be liberally sprayed anywhere, and it doesn’t cause any toxic reaction even if it’s sprayed on food. It doesn’t affect other organisms in the aquatic environment. You don’t want to kill the young fish. It’s specifically effective on mosquito larvae. It’s photodynamic as long as it’s in the tissue...

“Therefore, it cannot be liberally sprayed anywhere. If sprayed on food it kills other organisms it comes into contact with. It’s bad for pets also. But this compound could be liberally sprayed anywhere, and it doesn’t cause any toxic reaction even if it’s sprayed on food. It doesn’t affect other organisms in the aquatic environment. You don’t want to kill the young fish. It’s specifically effective on mosquito larvae. It’s photodynamic as long as it’s in the tissue and not exposed to sunlight. When the larvae feed on it, its not a toxic substance, but it becomes toxic the moment it is exposed to sunlight. Hence it’s a photodynamic larvacide,” Prof. Andradi explained.

Although Prof. Häder owns a US patent as well as a global patent for the compound, formalities would be time-consuming. 

On the one hand, several products have already dominated the local market and the compound has to be tested and approved by certain local authorities before it is available to the public.

Apart from that, several field tests need to be done, while observing any limitations and issues with shelf life. However, the scientific duo is positive about its progress given that the respective institutions are aware of its benefits and requirements within the prevailing conditions.