Epidemiology Distribution and Incidence

The epidemic of a highly fatal disease (later named Ebola virus disease) began in June 1976, with an index case in Nzara, southern Sudan, among workers in a cotton factory. This patient went to a large hospital in Maridi, where the disease spread rapidly among hospital patients and staff. The epidemic ran its course by November 1976. There were 148 deaths in 284 detected cases (52 percent mortality). In 1979 a further outbreak occurred in southern Sudan, with fewer cases and a small number of deaths.

The epidemic in Zaire was traced to an index case seen on September 1, 1976. The individual in question had received an intravenous injection of chloroquine for presumptive malaria with fever at the outpatient clinic of Yambuku Mission Hospital, Bumba District. He recovered, but within a week a large epidemic of fever began in hospital patients and staff. A total of 318 cases occurred, with 288 deaths (90.5 percent mortality). A number of inpatients and members of the hospital staff, physicians, and attendants also died. The epidemic had terminated by November 5, 1976. The diagnosis of the first epidemiological team sent to the area was "a fulminating epidemic of typhoid fever in a non-vaccinated population." Fatalities, however, occurred in a hospital in Kinshasa in the cases of three nurses who had been transferred from the infected area, and it became clear, as investigations continued, that passage of the virus from human to human had occurred through the medium of contaminated needles and syringes. Whereas formerly rigidly enforced isolation and barrier procedures had been somewhat relaxed, strict syringe and needle discipline and isolation of patients were reestablished and maintained as a permanent part of hospital operations protocol.

The epidemics in the Sudan and Zaire terminated as abruptly as they had started. However, in 1979 another hospital-centered outbreak occurred in Tan-dala, Zaire, 300 kilometers distant from the original Bumba outbreak. In total, 33 patients were diagnosed, of whom 22 died (66 percent mortality). Through the 1980s no further outbreaks have been reported in Sudan or Zaire or elsewhere in Africa, with the exception of a probable case from Kenya reported in 1983.

Complacency was shattered in the United States and internationally in early November 1989 when an epidemic, confirmed to be caused by Ebola virus, erupted in a shipment of 100 Macaca cynomolgus monkeys originating in the Philippines and shipped to a laboratory in Virginia, in the United States, via Amsterdam and J. F. Kennedy airports. Sixty of the 100 monkeys died. A second shipment received 2 to 3 weeks later in Virginia had two infected monkeys therein.

Extensive epidemiological explorations internationally have focused on this frightening episode. No human cases have been reported. At the time of writing (February 14,1990), no satisfactory explanations have been advanced. All exposed individuals are being monitored.

This demonstration of the danger of transmission of virus by use and reuse of inadequately sterilized needles and syringes has important implications for medical practice, not just in underdeveloped countries but also in developed cultures because of AIDS. Excessive parenteral administration of many drugs, which could be equally efficacious given by mouth, constitutes bad medical practice. Parenteral administration of drugs in medical emergencies is understandable and desirable. But such a practice for the "typical" patients seen at the clinic for undiagnosed fevers that are not immediately life-threatening is indefensible.

Unsophisticated patients unfortunately cherish an intuitive feeling that drugs, from vitamin preparations up the scale to specific therapeutic agents, are much more effective when given intradermally, subcutaneously, intramuscularly, or intravenously. Indeed, patients often demand parenteral administration of drugs and think poorly of a physician who does not oblige them. This view unfortunately is not discouraged by some practitioners of the medical arts, both licensed and unlicensed, and the practice also greatly increases the bill for pharmaceuticals benefiting drug companies and pharmacists. The poorer countries can ill afford the increased cost.

Epidemiologists have been active in trying to trace the origins of the Ebola virus and the distribution of the infection throughout Africa, locate host vertebrates other than humans, as well as learn methods of transmission to humans and the ways the virus is maintained and propagated in nature. Table VIII.42.1 summarizes these data. Although it may appear that much has been done, actually efforts have been limited to a handful of dedicated investigators, and to a scattered, spotty sampling of the vast expanse of Africa south of the Sahara.

Primates have been sampled (see Table VIII.42.1) and have revealed no involvement, or at best mini

Table VIII.42.1. Ebola serosurveys

Study area Date No. examined No. positive Percent positive Remarks

Humans

Study area Date No. examined No. positive Percent positive Remarks

Humans

Northern Senegal

1977

273

5

1.8

semidesert region

Zaire, Bumba province

1979

251

43

17

region of 1967 outbreak

Cent. African Republic

1980

499

17

3.4

several regions

Zaire, Tandala

1980

?

?

7

region of 1969 outbreak

Liberia

1982

400+

24

6

several regions

Zaire, Tandala

1982

138

7

5.1

Cameroons

1982

1517

-

3.2-23.5

several regions

Kenya

1983

52

2

4

Kenya

1983

741

8

1.1

Kenya

1986

471

46

10

in fever cases

Northern Sudan

1986

% of2000

?

v. few pos

desert region, north of out

break

Southern Sudan

1986

% of2000

?

15-30

in Maridi region; agricul

tural

Nigeria

1988

1677

30

1.8

several regions

Primates

Kenya

1982

136

0

0

monkeys of 3 species

Kenya

1982

184

3

1.6

baboons

Zaire

1981

200+

0

0

monkeys

Guinea pigs

Zaire, Tandala

1982

138

36

26.1

region of 1979 epidemic

mal involvement. In connection with the 1979 Tandala, Zaire, outbreak is the unexpected finding of guinea pig immunes. Guinea pigs are South American rodents, inquilines in human habitations in the high Andes. The inhabitants raise them for pets and for food. They were introduced to Africa decades ago and in some regions have established themselves as inquilines in houses. In this respect, their behavior resembles that of the abundant multimammate rat (Mastomys natalensis), already known to be involved in Lassa virus maintenance and spread to human beings. Guinea pig immune rates as high as 26.1 percent were found in these animals in some houses in Tandala. Study of the background of those who were positive, however, failed to indicate guinea pig-to-guinea pig transmission, guinea pig-to-human spread, or human-to-guinea pig spread.

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