A method of detecting sub-clinical avian necrotic enteritis, the method comprising determining the level of at least one marker indicative for necrotic enteritis in avian fecal excrements, wherein an increased level of this at least one marker in comparison to a non-infected control is indicative for necrotic enteritis and wherein the marker is selected from a) polynucleotides which have a sequence identity of at least 80 %, preferably at least 85, 90 or 95 %, most preferably 100 %, to a polynucleotide which consists of at least 20, preferably at least 25, 40, 60, 100, 150, 180 or 200, consecutive nucleotides of the nucleotide sequence as depicted in SEQ ID NO: 1, b) polynucleotides which have a sequence identity of at least 80 %, preferably at least 85, 90 or 95 %, most preferably 100 %, to a polynucleotide which consists of at least 20, preferably at least 25, 40, 60, 100, 150, 180 or 200, consecutive nucleotides of the nucleotide sequence as depicted in SEQ ID NO: 3, c) polynucleotides which have a sequence identity of at least 80 %, preferably at least 85, 90 or 95 %, most preferably 100 %, to a polynucleotide which consists of at least 20, preferably at least 25, 40, 60, 100, 150, 180 or 200, consecutive nucleotides of the nucleotide sequence as depicted in SEQ ID NO: 4; d) polynucleotides which have a sequence identity of at least 80 %, preferably at least 85, 90 or 95 %, most preferably 100 %, to a polynucleotide which consists of at least 20, preferably at least 25, 40, 60, 100, 150, 180 or 200, consecutive nucleotides of the nucleotide sequence as depicted in SEQ ID NO: 5; e) polynucleotides which have a sequence identity of at least 80 %, preferably at least 85, 90 or 95 %, most preferably 100 %, to a polynucleotide which consists of at least 20, preferably at least 25, 40, 60, 100, 150, 180 or 200, consecutive nucleotides of the nucleotide sequence as depicted in SEQ ID NO: 7; f) polynucleotides which have a sequence identity of at least 80 %, preferably at least 85, 90 or 95 %, most preferably 100 %, to a polynucleotide which consists of at least 20, preferably at least 25, 40, 60, 100, 150, 180 or 200, consecutive nucleotides of the nucleotide sequence as depicted in SEQ ID NO: 8; g) polynucleotides which have a sequence identity of at least 80 %, preferably at least 85, 90 or 95 %, most preferably 100 %, to a polynucleotide which consists of at least 20, preferably at least 25, 40, 60, 100, 150, 180 or 200, consecutive nucleotides of the nucleotide sequence as depicted in SEQ ID NO: 9; h) polynucleotides (DNAs and RNAs) which are complementary to the sequences according to (a) to (g); i) polynucleotides (DNAs and RNAs) which are complementary to the sequences according to (h); j) polynucleotides which comprise the polynucleotides according to (a) to (i). a) polynucleotides which have a sequence identity of at least 80 %, preferably at least 85, 90 or 95 %, most preferably 100 %, to a polynucleotide which consists of at least 20, preferably at least 25, 40, 60, 100, 150, 180 or 200, consecutive nucleotides of the nucleotide sequence as depicted in SEQ ID NO: 1, b) polynucleotides which have a sequence identity of at least 80 %, preferably at least 85, 90 or 95 %, most preferably 100 %, to a polynucleotide which consists of at least 20, preferably at least 25, 40, 60, 100, 150, 180 or 200, consecutive nucleotides of the nucleotide sequence as depicted in SEQ ID NO: 3, c) polynucleotides which have a sequence identity of at least 80 %, preferably at least 85, 90 or 95 %, most preferably 100 %, to a polynucleotide which consists of at least 20, preferably at least 25, 40, 60, 100, 150, 180 or 200, consecutive nucleotides of the nucleotide sequence as depicted in SEQ ID NO: 4; d) polynucleotides which have a sequence identity of at least 80 %, preferably at least 85, 90 or 95 %, most preferably 100 %, to a polynucleotide which consists of at least 20, preferably at least 25, 40, 60, 100, 150, 180 or 200, consecutive nucleotides of the nucleotide sequence as depicted in SEQ ID NO: 5; e) polynucleotides which have a sequence identity of at least 80 %, preferably at least 85, 90 or 95 %, most preferably 100 %, to a polynucleotide which consists of at least 20, preferably at least 25, 40, 60, 100, 150, 180 or 200, consecutive nucleotides of the nucleotide sequence as depicted in SEQ ID NO: 7; f) polynucleotides which have a sequence identity of at least 80 %, preferably at least 85, 90 or 95 %, most preferably 100 %, to a polynucleotide which consists of at least 20, preferably at least 25, 40, 60, 100, 150, 180 or 200, consecutive nucleotides of the nucleotide sequence as depicted in SEQ ID NO: 8; g) polynucleotides which have a sequence identity of at least 80 %, preferably at least 85, 90 or 95 %, most preferably 100 %, to a polynucleotide which consists of at least 20, preferably at least 25, 40, 60, 100, 150, 180 or 200, consecutive nucleotides of the nucleotide sequence as depicted in SEQ ID NO: 9; h) polynucleotides (DNAs and RNAs) which are complementary to the sequences according to (a) to (g); i) polynucleotides (DNAs and RNAs) which are complementary to the sequences according to (h); j) polynucleotides which comprise the polynucleotides according to (a) to (i).