Original articlePathology of the swine-origin influenza A (H1N1) flu
Introduction
The outbreak of the new swine-origin influenza A origin (H1N1) flu has been the first pandemic of the century, and has resulted in thousands of deaths through the world, involving many previously healthy young people [1]. Although the origin of this pathogen remains uncertain, an increase in the incidence of respiratory diseases was noted during March 2009 at the town of La Gloria, in the southeastern state of Veracruz in Mexico. It was probably the first community in which a case of novel influenza A H1N1 virus has been identified [2]. This virus has molecular features of North American and Eurasian swine, avian and human influenza virus, and was similar to the H1N1 virus of Spanish flu that had caused millions of deaths in 1918 and 1919 [3]. Some data support the hypothesis that the 1918 pandemic influenza virus was able to infect and replicate in swine, resulting in the current lineage of the classical H1N1 swine influenza viruses. These deaths are attributed to pneumonia and respiratory failure [4], [5]. There is also evidence that seasonal influenza infection is associated with increased deaths by certain conditions, including chronic heart disease [6], [7].
Although the causes are not completely understood, death from new swine-origin influenza A is more prevalent in patients with certain conditions, such as asthma, diabetes, and hypertension. A study of 574 deaths associated with pandemic H1N1 influenza suggests that the elderly may, to some extent, be protected from infection, and that there was an underlying disease in at least half of the fatal cases. This study also suggests that the major risk factors are pregnancy and metabolic condition, including obesity, which has not been considered as a risk factor in previous pandemics or seasonal influenza [8].
One important step to understand the poor outcome of the new influenza flu among people with these risk factors is to perform pathological autopsy studies using histological tests of different organs in severe cases. These studies would help to delineate adequate strategies for treating patients with poor clinical outcome of influenza A H1N1 swine flu. The objective of the present work is to describe these autopsy (histological) findings in 6 cases of patients with this disease.
Section snippets
Materials and methods
Autopsies of six cases of influenza A H1N1 swine flu were studied at the Pathology Department of the Emilio Ribas Institute (a reference center for infectious diseases) in Sao Paulo, Brazil. On hospital admission, five of these patients presented classical clinical symptoms of influenza flu (fever, muscle pain) plus persistent cough and dyspnea at the hospitalization that rapidly evolved to respiratory distress (adult respiratory distress syndrome) and required mechanical ventilation. One of
Results
The clinical data, laboratory tests, and autopsy findings of the cases of influenza A H1N1 swine flu are summarized in Table 1. Radiologically, there was extensive bilateral pneumonia with shadow nodules in all cases.
There were remarkable morphologic changes in the lungs of all patients. The lungs had extensive hemorrhagic appearance similar to red consolidation of lobular pneumonia (as red hepatization). The most important histological changes were alveolitis (and sometimes bronchiolitis),
Discussion
There was evidence that the swine-origin influenza (H1N1) virus is more pathogenic than seasonal influenza A virus, particularly in young people. This is due to a more extensive replication of this virus in the respiratory tract. Experimental data indicates that while replication of seasonal influenza A virus was restricted to the upper airway, swine-origin influenza A (H1N1) replicated also in trachea, bronchi, and bronchioles [11]. In addition, it was demonstrated that the 1918 influenza
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