<prompt> Cyclic trend is shown by -Polio epidemicRabiesInfluenza pandemicMalaria  <response>: Ans, is c i.e., Influenza pandemic Periodic fluctuationso Periodic fluctuation may be -Seasonal trendCyclic trendSeasonal trendo Some diseases show seasonal variations.o These changes are related to environmental conditions e.g., rainfall, overcrowding, humidity etc.o Examples are -i Measlesii Varicella chicken pox- Early springiii Upper respiratory tract infection - Winteriv GIT infection including poliov Cerebrospinal meningitisvi Rubella - late winter and springvii Dengue - in IndiaCyclic trendo Some diseases occur in cyclic spread over a short period of time which may be week, days, months or years,o This is due to naturally occuring variation in herd immunity.o A build up of susceptible is again required in the herd before there can be another attack,o It may be due to antigenic variations as occur in influenza,o Examples - Epidemic ofi Measlesii Rubellaiii Pandemic of influenza- every 2-3 years- every 6-9 years- every 10-15 yearsLong term or secular trendso The term secular trend implies changes in the occurrence of disease over a long period of time, generally several years or decades.o There may be progressive increase or decrease in the occurrence of disease,o Examples -CHD, lung cancer, and DM have shown a consistent upward trend in developed countries.TB, typhoid fever, diphtheria and polio have shown a declined trend in developed countries. 