(Bloomberg) -- McDonald’s, 7-Eleven and mayonnaise-maker Kewpie are just some of the firms in Japan contending with the worst-ever global outbreak of bird flu. 

Of 100 listed restaurant companies in Japan, 18 had suspended egg-related items as of March 5, according to Teikoku Databank. Fewer hens led to a near-doubling in the wholesale price of the farm staple to 327 yen ($2.37) a kilogram in February from the year before, the research firm said on Tuesday.

That means McDonald’s Holdings Co. Japan Ltd.’s Teritama Muffin is off the menu. The breakfast sandwich, which combines egg, sausage and teriyaki sauce, is typically offered in spring each year. The fast food giant has also warned it could temporarily halt sales of hamburgers that contain eggs if supply disruptions persist.

Japan is just one of many countries wrestling with an outbreak that’s sent egg prices skyrocketing in the US and caused a shortage of baby chicks in China. At a time of heightened inflation fears around the globe, the unprecedented spread of the disease is yet another reminder of the grim impact of pandemics on markets for food.

Japan confirmed its first case in October, beginning the earliest bird flu season the country has seen, according to the agriculture ministry. The disease has spread to over half the nation’s prefectures, forcing the cull of some 15 million birds, the ministry said.

7-Eleven, owned by Seven & i Holdings and one of the many convenience stores ubiquitous across Japan, suspended the sale of some egg products in January. Other measures have included swapping in vegetables for eggs in its tuna sandwiches, as well as increasing the portion of meat in its ham and egg offering.  

Condiment-makers Kewpie Corp. and Ajinomoto Co. have said they’ll raise prices from April for products like mayo and tartar sauce amid the surge in costs of one of their key ingredients. 

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