Orthomyxoviruses are the influenza viruses from the family Orthomyxoviradae. Various animal species become infected with their own specific strains of influenza, and, in some cases, the animal strains may produce mild infections in humans. Some of the human strains cause the more explosive and severe viral infection forms. The term “flu” is used to refer to a wide variety of infections, ranging from the common cold to various forms of enteritis.
There are three general types of influenza viruses, designated types A, B, and C.
- Causes the major outbreaks of influenza epidemics, and was discovered in 1933. Variants include New Jersey and Bankok. It has undergone two antigenic shifts, one in 1957 and the other in 1968.
- Causes moderate outbreaks and was isolated in 1940. A variation is the Hong Kong flu.
- Is relatively insignificant so far. It was discovered in 1947.
In type A, the inner core of the virion contains a helical capsid that surrounds an ss-RNA molecule. The RNA molecule is somewhat unique in that it is made up of eight loosely connected segments, with each segment containing the genetic information for the formation of a specific viral component. Of some importance are the two protein components (peplomers) that are embedded in the envelope and project out from the virus. It is these two proteins that are the immunity providers. One serves as the attachment site between the virus and the host cells, and is simply called the H antigen. The other is an enzyme called neuraminic acid, or the N antigen.
Antibodies formed against the H and N antigens are important protective antibodies. Minor mutations sometimes occur in the RNA segments that determine the configurations of the H and N antigens. These minor changes are called antigenic drift. When this occurs, the antibodies in the general population are less effective in providing immunity, and outbreaks of influenza develop. When a new subtype of the H or N antigen appears in a strain of influenza virus, it is called an antigenic shift. The origin of this has been theoretically attributed to the reassortment of the RNA segment between two different influenza subtypes simultaneously affecting the same host. When this happens, the protective antibodies that are already in the population are of no further value. The virus is then able to spread without restriction, and a pandemic of influenza results. Subtypes of type A influenza viruses that tell where and when they were first isolated as well as the antigenic composition are given. For example, A/Hong Kong/68 (H3N2) would be the influenza A subtype isolated in Hong Kong in 1968 with the H3 and N2 antigens.
Infection comes via the airborne route, with the viruses specifically attaching to the epithelial cells of the respiratory tract where they begin to grow, resulting in widespread inflammation. Infection is usually restricted to the upper respiratory tract, but will occasionally spread lower. In severe cases, the infection spreads to the blood or deeper body tissues where toxic products from the virus are absorbed into the blood, causing the generalized symptoms of influenza.
Influenza has a distinct clinical pattern that begins one to three days after exposure, starting with a sore throat, possibly hoarseness, and nasal discharge, followed by systemic symptoms of headache, fever, chills, generalized muscular aches, possibly some gastrointestinal distresses, and, in severe cases, prostration. Recovery takes aboutfour to seven days. Deaths are rare in healthy individuals, but can happen in the very young, elderly, and chronically ill. Since influenza weakens the natural defence mechanisms of the respiratory tract, it is common for such secondary infections as pneumonia to develop in those with compromised immune systems.
In 1932-33, epidemics occurred around the world. At that time, the first influenza virus from humans was isolated. The isolates from this period had the antigenic makeup of H1N1. Over the next twenty years, antigenic drifting occurred in these viruses, with limited epidemics resulting every three to four years, with a rather extensive epidemic occurring in 1947. The H1N1 subtype generally disappeared from the world population in the early 1950s. Major antigenic shifts occurred in 1957 in both the H and N antigens, resulting in a new subtype with H2N2 antigens. A prototype, called the “Asian flu,” developed, and, because there was no known antibody immunity, the disease spread rapidly within a year, causing major pandemics in most parts of the world. Epidemics continued every three or four years over the next ten years. In 1968, a major shift occurred in the H antigen, creating a subtype A/Hong Kong/68 (H3N2), commonly known as the “Hong Kong flu.” Like its predecessor, it swept to most parts of the world. To date, no other major antigenic shifts have occurred.
Unlike most viral diseases, early therapy of type A influenza can be accomplished with amantadine hydrochloride. This compound prevents the uncoating of the virus in host cells and so restricts its replication. Amantadine is also used prophylactically in high-risk persons. The compound, however, is not effective against either types B or C viruses.
The vaccines used for the influenza viruses are of limited value because of the specificity needed for each type of virus. The killed vaccine is only moderately effective in about 70% of the time and offers protection for only six months to a year. The vaccine contains toxic products of the virus that often induces mild symptoms of the influenza. Purified vaccines have only the H and N antigens and do not contain any of the toxic by products. When an antigenic shift occurs, the vaccines then in stock may be of no value. When a new subtype is found, a race begins between humans and the virus with the goal being to produce enough of the vaccine before the pandemic arrives. Those who are allergic to eggs should not accept flu shots since most of the vaccines are developed on chicken eggs.
The influenza virus has an uncommonly high mutation rate of up to one million times that of DNA. Only HIV mutates at a faster rate. Every year, as many as fifty million Americans contract the flu, with 10,000 to 40,000 dying. The Spanish flu of 1918-19 was the 20th century’s worst flu outbreak. Despite its name, it appears to have started in the US, and ended with the killing of an estimated twenty to forty million people. Almost half of those deaths occurred in India alone. Since no blood samples were saved, it will never be known exactly what type of virus caused the epidemic. However, autopsies revealed swollen, wet lungs filled with enormous quantities of thin, bloody fluid. The tiny air pockets that normally allow oxygen to enter the blood and carbon dioxide to leave it were full of fluid. The passages leading to the throat were filled with a bloody froth of fluid and air. The victims rapidly became cyanotic, beginning at the ears and spreading over the face. At the point of death, lung fluid would flood out and drench bed sheets. One unusual feature of this flu was that it preferred young people rather than the elderly, who are the usual targets.
In the 1970s, a major campaign was undertaken in the US against the “swine flu.” However, increased incidents of Guillain-Barre appeared at ten times the normal rate in those who had been vaccinated against the flu. The program was stopped after the government was forced to pay out millions of dollars in damages. Cross contamination from animals is always a threat, whether in the development of vaccines or directly. For example, in 1980, the virus produced an epidemic in seals, and caused conjunctivitis in humans who tried to help. Another interesting observation comes from Dr. Michael DeBakey of Baylor University. He saw that, in more than 15,000 patients, cholesterol was not the central cause of atherosclerotic heart disease. The underlying causes were not identified, but there appeared to be a distinct relationship between an abrupt rise in heart disease following an influenza epidemic.
Parainfluenza and respiratory syncytial viruses (RSV’s) include four types of viruses of interest. Generally, they cause lower respiratory diseases in children and upper respiratory infections in adults. In children, the most common form of the infection is called ‘croup.’ These viruses cause bronchiolitis and pneumonia that affect babies under six months old. It is the only virus that causes pediatric epidemics of respiratory disease every winter in cities, with the poor suffer the most.
Natural influenza treatments include the herb elder (Sambucus nigra), which has traditionally been used to treat colds and flu. The flowers from this plant have demonstrated antiviral and antiinflammatory activity against both A and B types of flu, as well as herpes simplex. The standardized elderberry extract, Sambucol, has proven to lessen the symptoms of the flu, with complete recovery in two or three days compared to a six-day recovery using other methods. Elder is speculated to stimulate the body’s own interferon or to prevent the virus from attaching to the body’s cell surfaces. In a study done with licorice root, mice were infected with lethal doses of influenza virus, and then treated with glycyrrhizin, an active component of licorice. It seemed to protect them from death. Also, they had less lung damage than those treated only with saline controls. As with any other illness, prevention is the best treatment. This involves healthy eating at all times, and not just when one expects trouble.