could someone explain that to me pls, why i have to use present perfect in this sentence.
He was thought … the disease in Hong Kong.
to catch
catching
to have caught
Alternatively , would that be possible to use infinitive in this sentence?
For ease of exposition, let T be the time when “He was thought to…” happened (i.e. the time when the person/people in question thought that thing). In your sentence, “to have caught” is presumably indicated because he caught the disease before time T.
You could say “He was thought to catch fish regularly”, in which case “catch” is concurrent with time T. However, “He was thought to catch the disease in Hong Kong” scarcely makes any sense because one can’t envisage his catching the disease concurrent with time T.
In this case, saying ‘he was thought to […]’ indicates the fact that it is definite that he doesn’t have the disease now. The present perfect agrees with this in that the event happened sometime between when ‘he was thought to’ and the present. You MIGHT use ‘to catch’; however, it’s best to use the most tense-correct verb(s), in this case ‘have caught’.
Thanks to both of you