Step One

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Create a new 500x200 document with a resolution of 150, fill it with white. Now go to Filter > Noise > Add Noise and change the amount to 180%, the distribution to gaussian, and check monochromatic.

Step Two

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Go to Filter > Noise > Median and set the radius to 4, click ok.

Step Three

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Choose Filter > Stylize > Glowing Edges and change the edge width to 1, the edge brightness to 10, and the smoothness to 10.

Step Four

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Now hit ctrl+u and check colorize, play around with the settings until you find something you like.

Step Five + Final Result

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Find an image that you would like to insert your infection in. Copy your step four image. Now, on the image you want to paste into, use the magic wand tool to make your selection. Go to Edit > Paste Into and transform your newly pasted image to your liking. Good luck