Anatomy of the plague

Anatomy of the plague IN ANCIENT times, it was seen as a curse from the gods. The Romans believed it to be a blast hurled down by one of their angered deities. In the 2nd century, at the height of the plague during the reign of Marcus Aurelius, the toll is said to have been 2,000 people a day, and finally contributed to the decline of the Roman empire.

The early Christians thought that the plague was divine punishment. For the Muslims, it became a symbol of martyrdom related to jihad, the holy war. After it rolled like unstoppable bushfire to the West, it was la morte nera, the Black Death. The horror of the Black Death was so enduring that even now, when there are proven ways to control a plague pandemic, the panic hasn"t lessened an iota.

The word "plague" is derived from "plaga", a blow. And this blow first struck in China and Inner Asia in the 10th century. Later it spread to Europe (AD 1347) as a result of the first recorded incident of biological warfare. The same year, in the seige of Caffa (now in Ukraine) in the Crimea, the Mongols catapulted corpses of plague victims over the walls of the Genoese defenders. And from the Mediterranean ports the plague spread to Sicily, North Africa, Italy, Spain, England, France, Austria, Hungary, Switzerland, Germany, Scandanavia and the Baltics.

According to the French chronicler Jean Froissart, "The first wave of plague in France reduced the population of the Normandy by two-thirds." Whole villages and communities were annihilated by this deadly disease. About 25 million people in Europe died from the plague; since then it has been referred to as the Black Death, sparing not even society"s highest. Even royalty, capable of faster flight, fell prey to it. Joan, the daughter of the English King, Edward III, died at Bordeaux on the way to her wedding. Canterbury lost 2 successive archbishops to plague.

Such horrific sights also had their influence on the philosophers and writers of the times. Albert Camus" 2nd novel, La Peste (1847) is a symbolic account of characters in Oran whose efforts to control the epidemic resulted in a determined assertion of human dignity and fraternity. In the Journal of the Plague Year (1722), Daniel Defoe has documented the events of the year of the Black Death.

Till then, all that was known was that plague is a highly contagious disease. So the only way to control it was be to isolate the victims and the suspected cases as well as those who had been in contact with the infected. The belongings of those who died were burnt to prevent the infection from spreading.

Strong measures were taken by healthy communities to prevent the entry of goods and people from an infected community. In AD 7, armed guards were stationed between plague-stricken Provence and the diocese of Cahors. The observation that the plague was generally spread by trading ships led to quarantining for the first time in Venice. At first the period of isolation was 14 days, gradually increased to 40 days. It is said that the choice of this period was based on the period that Christ and Moses spent in isolation in the desert. In modern times, a better understanding of communicable diseases has led to quarantine measures being modified.

Once, leprosy and tuberculosis aroused the same mindless panic. It isn"t as if this scare was unfounded, what with teeming tens of thousands falling victim to these diseases. In fact, it was the fear of such highly infectious diseases, a fear further aggravated by the onslaught of the plague, that stirred the public officials in Europe to create a system of sanitary controls to combat contagious diseases.

The pest identified
In 1894, Alexandre Yersin was one of the first to describe the plague bacillus, Pastuerella pestis (also called Yersina pestis or bacillus pestis). It was found that the rat flea (Xenopsylla cheipos) is the most efficient carrier of the plague. Field mice, gerbils, skunks and other small wild animals are the natural reservoirs of the disease. Over 200 species of flea are known to be infected by the plague bacillus, and an additional 10 species have been implicated as carriers of the classic-type urban plague.

Endemic foci of the plague exist in almost all continents: they are found in mountains, deserts, cultivated areas and forests in temperate and tropical regions. Usually, the disease is spread by resistant species of wild rodents, which have become immune to the plague. The black rat and the less susceptible gray sewer rat are commonly associated with the disease but are too vulnerable to allow its persistence -- the host is destroyed. However, the infection locates itself in relatively resistant wild rodents.

In India, foci of infection persist for periods of up to several years because the population of the wild rodents, species of gerbils, in which the disease occurs is not sufficiently resistant. Here, the plague reoccurs through the reintroduction of the parasite (rat flea) from permanent foci of infection elsewhere, usually by means of the highly susceptible rat, which transmits the infection to the indigenous gerbil population. The gerbils then pass the infection to other field and urban rats. When these rats become victims of the plague and start dropping dead, it is a clear indication that the plague might hit the human population.

A flea, a rat and the world
The rat flea is a parasite that ingests the blood of the host rodent and thereby gets infected by the plague bacillus. Thus when the rats fall victim to the plague, the flea turns to human beings as its new host. But why does it attack humans? Simple: because it has to find a host within jumping distance, as the flea cannot fly.

Human plague has been reported from the United States as well as several Southeast Asian countries, including Indonesia, Myanmar and Vietnam. However, epidemics of the kind that is being seen in India are rare.

Often, the spread of the plague has been attributed to social factors. For example, in 1967, 94 per cent of the world total of human plague cases occurred in Vietnam. Several years of military operations are said to have indirectly resulted in a plague epidemic.

Generally, plague outbreaks have been related to the seasons. For instance, in northern India, the plague season falls between September and May. This curious seasonality of the disease is because from May onwards, the field rodents close themselves in their burrows and live on stored food reserves. Then the epizootic ceases to advance and at the same time infection of the village rats comes to an end. Field rodents become active again in mid-October, when the monsoon floods dry up. The epizootic is revived in the fields.

The most favourable weather conditions are a mean temperature of 20 to 25 degrees Celsius, and a relative humidity of 60 per cent and above. Human beings have not developed any natural immunity against the plague, which occurs in 2 main forms. One is the bubonic plague, which asserts itself 2-6 days after the bite of an infected flea. It is identified by a sudden onset of fever and intense pain in any anatomic region of lymph nodes -- axilla, groin or neck. Untreated bubonic plague can allow the bacterium to enter the bloodstream and cause clotting of the blood throughout the circulatory system. This is called septicaemia plague.

The other form, the pneumonic plague, is highly infectious. It becomes fatal when antibiotic therapy is delayed for more than 20 hours after the onset of the illness. Tetracycline, chloramphenicol, cotrimoxazole, sulphonamides and streptomycin are some of the drugs that are used to treat the plague.

While 2 vaccines, Haffkine and live virulent cultures of the EV strain, are available their effectiveness is not well established, which is why mass vaccination is not recommended. But it has been used under highly endemic conditions or for high risk groups vaccination, and may be given for individual protection. Nevertheless, US troops in Vietnam were vaccinated and had a much lower incidence of the plague than the Vietnamese. The immunity conferred is of short duration, about 6 months. To maintain immunity, revaccination is necessary and must be spread over a period and reinforced by booster injections. Often, high risk groups like laboratory workers are given preventive shots.

However, the most effective way to prevent an epidemic of plague is to reduce the rodent population. And this can be done only through improvements in sanitation, proper waste disposal, and proper storage of grain and foodstuffs. Sometimes, to control an epidemic rats are trapped and rodenticides are used. But such methods are ineffective in places which have a large rodent population. Bombay alone has a rat population of about 5 crore, and it"s a wonder that it hasn"t fallen prey to the plague.