Ans. is 'a' i.e., Caused by Human Herpes Virus-3 o Chickenpox is caused by varicella zoster virus (Human Herpes Virus-Ill or Herpes simplex tvpe-III).Chicken poxo Causative agento Portal of entryo I. P.o Infectious periodo Secondary attack rate is higho Age group- varicella zoster virus (Herpes simplex type III)- Respiratory tract or conjunctiva- 10-21 days.- 2 days before and 5 days after the onset of rash.- 90%-5-9 Yrs.o C/Fs - has two stagesPre-eruptive stagefever, back pain, malaise, shiveringEruptive stageRash is symmetrical, mostly on flexor surface.Centripetal in distributionMainly On trunk, less common on arms and legPalms and soles are not usually affectedThere is rapid evolution of rashRash is plemorphic, that is, all stages of rash (Papule, vesicle and crusts) may be seen simultaneously.Disease is more severe in adults than in children.Differences between smallpox and chickenpoxSmallpoxChickenpox1 Incubation:About 12 days(range : 7-17 days)About 15 days(range : 7-21 days)2. Prodromol symptoms :Severe.Usually mild.3. Distribution of rash:a) Centrifugalb) Palms and soles frequently involved.c) Axilla usually freed) Rash predominant on extensor surfaces and bony prominences.a) Centripetalb) Seldom affectedc) Axilla affectedd) Rash mostly on flexor surfaces.4. Characteristics of the rash:a) Deep-seatedb) Vesicles multilocular and umbilicatedc) Only one stage of rash may be seen at one time.a) Superficialb) Unilocular; dew-drop like appearance.c) Rash pleomorphic, i.e., different stages of the rash evident at one given time, because rash appears in successive crops.d) An area of inflammation is seen around the vesicles.d) No area of inflammation is seen around the vesicles.5. Evolution of rash:a) Evolution of rash is slow, deliberate and majestic, passing through definite stages of macule, papule, vesicle and pustule.b) Scabs begin to form 10-14 days after the rash appears.a) Evolution of rash very rapid.b) Scabs begin to form 4-7 days after the rash appears.6. Fever:Fever subsides with the appearance of rash, but may rise again in the pustular stage (secondary rise of fever).Temperature rises with each fresh crop of rash.