Glossary entry (derived from question below)
English term or phrase:
challenging
Portuguese translation:
estímulo
English term
expert in patents; chemical engineer
Native in: Portuguese 
Works in: English to Portuguese, French to Portuguese
challenging
Exposing an animal to a prototype vaccine is known as "challenging".
Oct 16, 2008 12:57: Maria Meneses Created KOG entry
Proposed translations
Norway
Salvador Scofano and Gry Midttun
Engineer:Oil&Gas/Electron/Finan/Law/HSEQ
Native in: Norwegian 
, Portuguese
Works in: English to Portuguese, Norwegian to Portuguese, Portuguese to Norwegian, and 19 more.
teste de resposta (ou de reação), teste da vacina
| agree |
Catarina Maia
: Teste de resposta/reacção à vacina
4 mins
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Obrigado pela observação
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| agree |
Roberto Cavalcanti
48 mins
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Obrigado
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| agree |
Lucio C P Soluchinsky
3 hrs
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Obrigado
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| agree |
Carlos Quandt
20 hrs
|
translator + journalist=flawless writing
Native in: Portuguese
Works in: English to Portuguese, French to Portuguese, Portuguese, and 1 more.
é um desafio/estimulante
| agree |
Adam Prus-Szczepanowski
: Diria que é um "desafio"
1 min
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Obrigada, Adam
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| agree |
Sara Sousa Soares
: concordo! http://cascavel.cpd.ufsm.br/tede/tde_oai/oai2.php?verb=GetRe...
9 mins
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Obrigada, Sara!
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| agree |
Ligia Dias Costa
15 mins
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Obrigada, Lígia
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| agree |
Soraia Martins
29 mins
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Obrigada, Soraia
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| agree |
Sonia Heidemann
4 hrs
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Portugal
Affordable high quality and dedication
Native in: Portuguese (Variant: European/Portugal)
Works in: English to Portuguese, French to Portuguese, Spanish to Portuguese
provocar / provocação
Segundo o IATE, "challenge" neste caso específico significa "provocar". Ver também ligações.
http://www.spaic.pt/download.php?path=pdfs&filename=LB_2000_0_46_Cenarios_medido-cientificos.pdf
United States
Marlene Curtis
Native in: Portuguese , English
Works in: English to Portuguese, Portuguese to English
controverso/controvertido
Portugal
Maria Teresa Borges de Almeida 
30+ years translating EU documents
Native in: Portuguese (Variant: European/Portugal)
Works in: English to Portuguese, French to Portuguese, Spanish to Portuguese, and 1 more.
melindroso
Brazil
PT/EN Translator - ABRATES Certified
Native in: English (Variants: UK, British) , Portuguese (Variant: Brazilian)
Works in: Portuguese to English, English to Portuguese
Discussion
Um profissional da matéria deu-me uma resposta que me parece correcta: estímulo (de resposta imunitária) ou reforço no caso de ser dado uma segunda vez