Mice Footpad Injection: Introduction, Test Requirements, Test Procedure, Application and Keynotes

Introduction of Mice Footpad Injection

Mice footpad injection is an important route of inoculation in mice models of disease and immunology.  Mice Footpad Injection or inoculation is a common experiment in Leprosy. As M. leprae cannot be cultured in-vitro but does grow on the footpads of mice, a conventional mouse colony was introduced to perform culture and sensitivity testing of M. leprae. In 1982 a nude mice colony was introduced to facilitate new drug trials for leprosy. Swiss Albino mice are the most common in practice.

 Test Requirements for Mice Footpad Injection

• 26G hypodermic needle
• 1 ml syringe
• Gloves
• Goggles
• Apron
• Mask
• Sprit cotton
• Suspension for inoculation ( test organism/ drug)
• Disposal bucket
• Mice (Swiss Albino mice or nude mice)

Test procedure of Mice Footpad Injection

1. Fill the syringe with an appropriate amount of suspension for inoculation. The maximum volume that can be injected into a footpad is 50 µl.
2. The mice are placed in a restraint tube with one hind foot isolated and extended by grasping the skin above the stifle.
3. Wipe the foot with a spirit swab to remove debris prior to injecting.
4. Grasp the toes of the extended foot prior to releasing the skin at the stifle.
5. Inject subcutaneously into the center of the hindfoot forming a small bleb at the injection site.
6. Once the suspension has been delivered, remove the needle and observe for bleeding.
7. Give light pressure to the puncture site if bleeding occurs.
8. Return the mice to the cage.
9. Enter the data in the datasheet.
10.  Check the inoculated mice daily for a week ( depending on the nature of your experiment).

Applications of Mice Footpad Injection

• Mice foot inoculation of M. leparae for cultivation and drug testing.
• They are also the experimental animal models for new drug trials of leprosy.
• To study Viral-Induced Neuroinflammatory Responses.

Keynotes on Mice Footpad Injection,

• Only one hind foot is preferred and thus never inject both hind feet.
• Nude mice maintenance is cumbersome since they are highly sensitive.
• The needle is injected just off the midline parallel to the vessel to avoid rupturing the blood vessel that runs the length of the foot.
• Patients are selected for Mycobacterium tuberculosis culture and sensitivity on the following criteria-

1. Untreated new patient: Borderline Lepromatous (BL)/Lepromatous leprosy (LL) who have a bacteriological index (BI) > 3+
2. Relapsed patient: BL/LL who have BI > 3+
3. Patient not responding to therapy: BL/LL who have BI > 3+
4. Defaulter

• The mice must be closely monitored for signs of pain, level of food consumption, and for normal ambulation.
• Self-mutilation can occur with the foot being chewed off. This is a sign of chronic pain. Any mouse demonstrating self-mutilation should be monitored by the animal house representator or the veterinary staff immediately.
• The mice must be euthanized when the lesion or tumor reaches the protocol endpoint or interferes with the mice’s ability to ambulate or reach food and water.

Further Readings

• https://link.springer.com/protocol/10.1007/978-1-62703-481-4_12
• https://www.researchgate.net/publication/7065440_The_mouse_foot-pad_technique_for_cultivation_of_Mycobacterium_leprae
• https://www.jove.com/t/61121/mouse-footpad-inoculation-model-to-study-viral-induced
• http://ila.ilsl.br/pdfs/v55n4s1a08.pdf
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2464360/