A disease that weakens bodys defense system against infection .

There are various diseases that weakens body's defence system against infection such as rheumatism, aids, hepatitis C etc.

For more information refer the link below:
https://www.meritnation.com/ask-answer/question/expert-please-answer-this-question-now-rheumatism-is-a/science/5376509

https://www.meritnation.com/ask-answer/question/why-aids-attack-on-immune-system-and-what-do-mean-by-a-synd/why-do-we-fall-ill/6832217