During the last century there were three other pandemics: the well-known, and erroneously called “Spanish flu”, which debuted in a military training center (Fort Ridley, Kansas, United States) on March 4, 1918, and that oscillatingly remained until almost 1920; and the pandemic flu of the years 1957, 1968 and 2009. [Existieron otras que los científicos califican como seudopandemias por su escasa relevancia, la de 1947 y la del bienio 1977-1978].
There is, however, another almost forgotten flu pandemic, the appropriately named “Russian flu”, that arose in Saint Petersburg (Russia) in another month of March, in the year 1889. The initial morbidity and mortality records came mainly from those provided by the European armies (especially French, British and German) together with the information obtained from the cities of the Helvetic Confederation (Switzerland). Despite the times, the “Russian flu” reached the United States seventy days after its appearance in St. Petersburg; and in just four months he circumnavigated the entire planet. Their mortality was estimated between 0.1 and 0.28% (with great variability between different cities), similar to that of the subsequent influenza pandemics of 1957 and 1968; and ten times less than that of 1918, highly conditioned by the First World War. The mortality estimate for the “Spanish flu” is highly variable depending on the source consulted, frequently using the figure of fifty million deaths, a number higher than that of the direct victims of the Great War.
The 2009 A / H1N1 flu was considered a pandemic when the World Health Organization (WHO) on June 11, 2009, it raised the alert to level 6, the maximum. This episode was added to eleven other pandemics that occurred during the 18th, 19th and 20th centuries. The time intervals between pandemics ranged from 8 years (between the pandemics of 1781 and 1789), to 42 years, the longest inter-pandemic period (between those of 1847 and 1889), and only one year less (41) was the time between 1968 and 2009. In any case, all these pandemics were caused by different strains (genetic variants) of the influenza virus.
Many studies and concepts about pandemics emerged from the “Spanish flu.” Among them the “basic reproduction number” (R 0) that indicates how many people are infected (on average) from one infected. It was also the first time that monthly surveys were conducted in Germany; on January 5 in Paris; reaching January 12 (the duration of a transatlantic voyage) United States.
There are very few studies of the pandemics of the years 1957 and 1968; still less of the 1889-1890 pandemic, the “Russian flu,” possibly caused by the H3N8 strain. The route by which this flu spread through Europe was the railroad. The 19 European countries, including Russia, were interconnected by 202,887 kilometers of railways, much more than today. It was the transmission route in Europe. The peak of mortality in Saint Petersburg occurred around December 1 (1889); the 22 of the same month in Germany; on January 5 in Paris; reaching January 12 (the duration of a transatlantic voyage) United States.
Transatlantic voyages took less than six days in relation to a current day (counting the change of time zones), a minimal difference, in any case, for the spread of a virus with pandemic potential.
The experience of the “Russian flu” taught that travel restrictions have, if anything, a very modest effect in slowing the spread of the virus. This calls into question some of the current mobility restrictions, taken with more political than truly scientific criteria.
There are other aspects that are undoubtedly more important, such as latitude (determining the climate), the number of people who share the same home, and hygiene habits (determining socioeconomic status).
With regard to the current Covid-19 pandemic, one of the aspects that creates more confusion is what can be considered as true symptoms of the infection.
When they arose the first cases in the city of Wuhan (Hubei province, People’s Republic of China) was classified as an atypical pneumonia, ignoring other symptoms. In light of current experience, it is estimated that up to 86% of all cases in China were lost (not taken into account).
In a variable, but not negligible, percentage of patients (between 2 and 40%) the first symptom is diarrhea. It is unknown whether the virus directly affects the cells that line the digestive tract, or is a consequence of previous involvement of the central nervous system, or is the result of the massive secretion of cytokines (molecules that mediate the immune response).
The virus has been detected in the feces, indicating a possible fecal-oral transmission, which is why personal hygiene must be extreme. Another well-known effect of infection (sometimes the first and only symptom) is the loss of the sense of smell (anosmia) that is observed in around 53% of those infected, with a higher incidence in young people. In some images obtained by nuclear magnetic resonance, inflammatory obstruction of the olfactory clefts is observed, without visible alteration of the olfactory bulb.
Note that anosmia is relatively common in many viral infections of the respiratory tract. Animal experiments have shown that the olfactory nerve (1st cranial nerve) is the most likely route by which the SARS-CoV-2 virus invades brain tissue, causing neuronal damage, usually fatal.
32% of patients
A growing number of scientific reports report neurological symptoms (stroke, ischemic or hemorrhagic, vertigo, severe headache, confusion, Guillain-Barré síndrome, and acute necrotizing encephalopathy. Sometimes this host of serious neurological effects is not linked to viral invasion of nervous tissue.
Cardiovascular disease associated with covid-19 includes myocardial inflammation (myocarditis), arrhythmias and even heart failure. Some studies carried out in China have shown a state of hypercoagulation with cases of thrombophlebitis and venous thrombosis. An indicative symptom of the risk of embolism is chest pain. Ocular manifestations (hyperemia, conjunctival edema) have been observed in approximately 32% of patients, in agreement with the detection of viral RNA in tears.
For unknown reasons, children do not become ill or their infections are mostly asymptomatic, except for severe, very rare cases of multiple organ failure (multisystem).
On the other hand, in the elderly many signs and symptoms can remain masked, delaying its diagnosis and worsening its evolution. For example, pneumonia in an elderly person can present with a mild or moderate fever, prone to a fall or a state of confusion. A matter not yet estimated is the risk of transmission of asymptomatic infected.
On the other hand, similar viral loads have been detected in patients, people with mild symptoms or without any symptoms. It is considered that more than 12% of all infections occur when the transmitting person is asymptomatic. In these circumstances, it is very difficult to stop the spread of the infection, which will probably follow its natural evolution. Remember that the SARS-CoV-1 epidemic of 2003 did not acquire pandemic expansion because only symptomatic people spread the infection.
**José Manuel López Tricas is specialist pharmacist Hospital Pharmacy. Las Fuentes Pharmacy (Zaragoza)