(Adds new cases of dairy herds and humans infected)

July 22 (Reuters) - The H5N1 bird flu virus has spread

to dairy cows in the United States, raising concerns about its

spread to humans.

Since 2022, bird flu in the U.S. has infected 168 dairy

herds, 7 people who were exposed to poultry, 4 people who were

in close contact with infected cattle, more than 100 million

chickens and over 9,500 wild birds.

The following is a timeline of the current outbreak in the

country:

July 19

The U.S. Centers for Disease Control and Prevention on

Friday confirmed two additional cases of bird flu in Colorado

poultry farm workers in addition to four previously confirmed

human cases in the state this year.

The health agency also said preliminary results from blood

samples collected from 35 people who work in dairy farms in

Michigan with infected herds did not show neutralizing

antibodies specific to the H5N1 virus, an indication that the

disease was not present in a wider group.

July 15

Oklahoma became the 13th U.S. state to detect bird flu in

dairy cows, the U.S. Department of Agriculture confirmed.

July 2

The U.S. government awarded $176 million to Moderna ( MRNA )

to advance development of its bird flu vaccine.

June 7

Wyoming became the 12th state to report an infected dairy

herd.

June 6

Minnesota became the 11th state to report an infected dairy

herd.

June 5

Bird flu outbreak in dairy cows expanded to a 10th state as

Iowa reported its first infection in a herd.

May 30

A third U.S. dairy worker tested positive for bird flu in

2024 after exposure to infected cows, and was the first to

suffer respiratory problems. The infection was the second human

case in the state of Michigan.

May 22

Another human case of bird flu is confirmed in the U.S. with

the infection of a dairy worker in Michigan. It is the second

case in humans this year after the virus was detected in cattle.

April 26

Colorado became the ninth U.S. state to report an infected

dairy herd.

April 25

Colombia restricted the import of beef and beef products

coming from U.S. states due to bird flu in dairy cows.

April 24

The U.S. government said it will require dairy cattle moving

between states to be tested for bird flu.

April 23

The U.S. Food and Drug administration said it had found bird

flu virus particles in some samples of pasteurized milk, but

said the commercial milk supply remains safe due to

pasteurization.

April 11

South Dakota became the eighth U.S. state to find avian

influenza in a dairy herd, after the U.S. Department of

Agriculture (USDA) reported infections in North Carolina, Texas,

Kansas, Ohio, Michigan, Idaho and New Mexico.

April 4

Bird flu dairy cow outbreak widened to a dairy herd in Ohio.

April 2

Mexico's agriculture ministry said it was taking

preventative measures to increase surveillance and reinforce

inspections of U.S. livestock imports after bird flu was found

in dairy cattle there.

April 1

The second known human case of bird flu in the United States

is reported in a person from Texas who had contact with dairy

cows presumed to be infected with the virus.

The virus was detected in dairy cattle in New Mexico,

Michigan and Idaho, along with Texas and Kansas.

March 25

The USDA said samples of milk collected from sick cattle in

Kansas and Texas tested positive for avian flu, but the nation's

milk supply was safe.

Dec. 12, 2023

Egg producer Cal-Maine Foods ( CALM ) said it had

temporarily ceased production at a facility in Kansas after some

of the flock tested positive for avian flu.

Nov. 3, 2023

Arkansas, a major U.S. chicken producer, reported its first

outbreak of lethal avian flu in a commercial poultry flock in a

year.

Oct. 6, 2023

The United States detected its first case of avian flu on a

commercial poultry farm since April, in a flock of 47,300

turkeys in Jerauld County, South Dakota.

April 14, 2023

The U.S. government said it was testing four potential bird

flu vaccines for poultry, after more than 58 million chickens,

turkeys and other birds had died in the nation's worst outbreak

ever.

March 20, 2023

Some of the world's leading makers of flu vaccines say they

could make hundreds of millions of bird flu shots for humans

within months if a new strain of avian influenza ever jumps

across the species divide.

Oct. 7, 2022

Avian flu infected a commercial flock of breeding chickens

in Arkansas, widening an outbreak of the disease in the southern

region.

Nationwide, more than 47 million birds have been killed by

avian flu or culled to control its spread this year in the

nation's worst outbreak since a record 50 million birds were

wiped out in 2015.

April 29, 2022

The first known human case of H5N1 bird flu in the United

States appeared in a person in Colorado, who was involved in

culling birds at a commercial poultry facility.

March 7, 2022

More than 22 million commercially raised U.S. chickens and

turkeys have been killed since February 2022 due to outbreaks of

a highly lethal type of bird flu.

March 4, 2022

A bird flu outbreak is reported in a commercial flock of

chickens being raised for meat in Stoddard County, Missouri,

taking the spread of the virus to 10 commercial chicken and

turkey farms in four states.

Feb. 9 , 2022

The USDA reported an outbreak of highly pathogenic avian flu

in an Indiana turkey flock, the nation's first case in a

commercial poultry operation since 2020.