Brazil is investigating another four new potential cases of highly pathogenic avian influenza (H5N1) in wild birds, according to authorities from the state of Espirito Santo, where Brazil's first ever cases were confirmed this week, reported Reuters.

After the birds showed symptoms consistent with H5N1, samples were taken from the four, all of them from the Thalasseus acuflavidus species (Cabot's terns), according to a statement from Espirito Santo's Agriculture, Supply, Aquaculture and Fisheries agency on Friday.

The samples are being processed by a reference lab of the World Organization for Animal Health (WOAH) in the city of Campinas. State authorities expect to get test results back sometime next week.

As part Brazil's National Avian Influenza Surveillance Plan, Espirito Santo said it is mapping out "focus areas" and inspecting properties, public or private, where birds can be found.

A case of the highly infectious avian influenza on a farm usually results in the entire flock being killed and can trigger trade restrictions. Detection among wild birds does not spark bans under WOAH guidelines.

Espirito Santo is Brazil's third biggest egg producing state and Brazil is the world's biggest chicken exporter.

The birds whose samples are now being processed were captured in the municipalities of Nova Venecia, Itapemirim, Linhares and Vitoria, Espirito Santo authorities said.

Some 26 birds being kept at Espirito Santo's rehab center for wild species, Ipram, were culled to contain potential transmission, the statement added.

Ipram is where the weakened shore birds were taken before Brazil announced its first cases of highly pathogenic avian influenza on Monday.

The virus arrived in South America through migratory birds. Normally, these animals will only spread bird flu for around five days but the virus' presence in small sea life the birds feed on may have enabled its broader spread this year.