The 1929–1930 psittacosis pandemic, also known as the psittacosis outbreak of 1929–1930 and the great parrot fever pandemic,^[2] was a series of simultaneous outbreaks of psittacosis (parrot fever) which, accelerated by the breeding and transportation of birds in crowded containers for the purpose of trade, was initially seen to have its origin in parrots from South America. It was shortly found to have spread from several species of birds from several countries worldwide to humans between mid 1929 and early 1930. Diagnosed by its clinical features and link to birds, it affected around 750 to 800 people globally, with a mortality of 15%. Its mode of transmission to humans by mouth-to-beak contact or inhaling dried bird secretions and droppings was not known at the time. The cause, Chlamydia psittaci, which usually remains dormant in birds until activated by stress of capture and confinement, was discovered after the pandemic.

Cases of psittacosis were reported in mid 1929, in Birmingham, United Kingdom, and linked to parrots from Buenos Aires, Argentina, where an ongoing outbreak of the disease had led to cautioning bird owners to declare their sick parrots. The origin of the outbreak in the Argentine city of Córdoba was traced to an import of 5,000 parrots from Brazil. Although the Argentine parrot trade was stopped, a number of birds were illegally sold on to visitors at its seaports, with the consequence that psittacosis was transmitted to several countries.

In November 1929, reports of cases among an Argentine theatrical group in Córdoba made it into the local press. In January 1930, when cases of an atypical pneumonia in one family, with the death of their parrot, appeared in Maryland, United States, a link was made to the story of the theatrical group, and "parrot fever" made headlines in the American press. Following further cases, bans on parrot trades were implemented, and subsequently cases were reported in several other countries, including Germany, France and Australia. The origin was understood to have been the importation of green Amazon parrots from South America. Later, the principal source of the disease in the U.S. was domestic lovebirds raised in Californian aviaries.

The impact of the outbreak on the U.S. Hygienic Laboratory, with 16 of its workers affected, including two deaths, led to the formation of the National Institute of Health.

In 1880, physician Jakob Ritter described a cluster of seven people with atypical pneumonia connected to his brother's household in Germany. The outbreak was at the time not linked to sick exotic birds: 12 finches and parrots confined in the study of the house in Uster, Switzerland. Three of the seven affected people died, including Ritter's brother and the metal-worker who visited the home to fix the bird cage. Ritter detailed the natural history of the disease, and, noting its similar features to typhoid and typhus, he called the disease "pneumotyphus" and proposed that the birds might be the vectors.^[3][4][5] Subsequently, further similar outbreaks with a coincidence of exposure to birds appeared in other parts of Europe, including Paris in the 1890s, where it killed one in three affected people. The outbreaks ended following bans in bird trading. Subsequently, greater efforts were made to find the cause of the disease, but without success. The disease in birds was named psittacosis in 1895 by Antonin Morange. Prior to the 1929 outbreak of psittacosis in the United States, the last known cases were in 1917, found in captive birds in the basement of a department store in Pennsylvania.^[4] The causative pathogen, C. psittaci, was not discovered until the 1960s.^[2][6][7]

There were multiple origins, involving several countries and several species of birds.^[4] Affected people typically experienced headache, poor sleep, fatigue and a cough trailing several days of fever. Some subsequently became delirious and semi-conscious, after which some died, and others recovered with a prolonged convalescent period.^[2]

Initial outbreaks were linked to exotic birds from South America.^[2] The source of the Córdoba outbreak was traced to an import of 5,000 parrots from Brazil. The birds had been confined in unsanitary and crowded containers. Although the Argentine parrot trade was stopped, a number of birds were sold on to visitors to its seaports, and psittacosis, also known as parrot fever, was transmitted to several countries. Its mode of transmission to humans by mouth-to-beak contact or inhaling dried bird secretions and droppings was not known at the time.^[2][8] Germany, the United Kingdom and the United States were the most severely affected with more than 100 cases each. Implicated birds included green Amazon parrots, canaries, lovebirds and shell parakeets.^[9][10]

By early 1930, the disease was reported in humans in several countries around the world, accelerated by the popular hobby of domestic bird-keeping at the time. Many cases and clusters had links with sick parrots. Around 750 to 800 people were affected. The average mortality was 15%, with a total of more than 100 deaths.^[2][11]

The majority of cases in the U.S. were found in 1931 to be linked to endemic psittacosis in California, associated with the increasingly popular trade of breeding lovebirds for sale chiefly to housewives and widows.^[2][8]

When cases appeared in Amsterdam, Netherlands Health Department asked that steamships that call at South American seaports refuse to take on board parrots.^[13]

In 1929, around 500,000 canaries and nearly 50,000 parrots were imported to the United States from Brazil, Argentina, Colombia, Cuba, Trinidad, Salvador, Mexico and Japan. Most birds entered the U.S. via New York, except budgerigars, which entered via San Francisco and Los Angeles.^[2]

The first reports of the disease were recorded in July 1929, in Córdoba, Argentina.^[14] During the summer and autumn of 1929, Córdoba and Tucumán in Argentina, reported over 100 cases of a severe atypical pneumonia linked to a large shipment of birds from Brazil.^[2][4]

One of the outbreaks occurred among an Argentine theatrical group in October 1929, after they had purchased an Amazon parrot in Buenos Aires. Two of the actors died from the illness.^[14] Florencio Parravicini, the main male actor, contracted the disease and according to the Hearst, recovered after suffering significantly for 17 days. Cases in Argentina followed a number of auctions that took place in several cities, with owners selling a number of sick birds as quickly as possible. In response, the Argentine parrot trade was stopped and pet owners were cautioned by authorities to look out for sick birds and report them. However, dishonest traders continued to sell sick birds to visitors to its seaports. The cases were reported in an Argentinian journal in November 1929 and later picked up by sensational American press.^{[2][4][28][29]}

There were no reported cases in Brazil.^[2] The disease was reported in:^[4][2]

Meyer later demonstrated that psittacosis could be transmitted by around 50 species of birds.^[6] Birds implicated in the 1929–30 pandemic included:

• Amazon parrots (Amazona species)^[4]
• Canary (Serinus canaria)^[4]
• Lovebirds (Agapornis species)^[4]
• Shell parakeets (Australian budgerigars, Melopsittacus undulatus).^[4][8]
• Talking parrots^[4]
• Grey parrots^[16] (Psittacus erithacus)
• Thrushes^[16]