THE RELATION OF GOAT'S MILK TO THE SPREAD OF

MALTA FEVER.

By JOHN F. ANDERSON.

Passed Assistant Surgeon and Assistant Director Hygienic Laboratory, Public Health and Marine-Hospital Service.

Recently it has been shown that Malta fever is conveyed by means of the milk of goats infected with the specific organism of the disease. While the disease may undoubtedly be spread by other means, the use of infected goat's milk in Malta is by far the most important factor.

Malta fever is a specific febrile infection caused by the Micrococcus melitensis discovered by Bruce in 1887. The fever is of an irregular, recurring or undulating type; in a typical case it lasts for several weeks, followed by a period of a few days or weeks of a relative apyrexia, which is again followed by other febrile periods.

Clinically, Malta fever is usually characterized by profuse perspiration, constipation, frequent relapses, often accompanied by pains of a rheumatic or neuralgic character, sometimes swelling of joints or orchitis. The disease is characterized by low mortality and indefinite duration.

Malta fever smolders endemically on the island of Malta, at Gibraltar, and other places on the Mediterranean basin. At times the number of cases at one place constitutes an epidemic. Bruce believes that one attack confers a definite immunity against subsequent attacks. Strangers particularly, visiting in the endemic focus, are liable to infection. On account of the almost invariable tendency to undulations of pyrexial intensity Malta fever is often called "undulating fever," a name proposed by Hughes. The disease is also known as Gibraltar fever, Mediterranean fever, rock fever, etc., depending upon the locality.

The following is a list of places from which Malta fever has been reported: "

Spain-Gibraltar; Islands of the Mediterranean-Balearic Islands, Corsica, Sardinia, Sicily, Malta, Gozo, Cyprus, Crete; Italy-—Rome, Naples, Caserta, Benevento, Campobosso, Aricca, Terano, Fermo, Padua, Cittanova, etc.; Greece-Athens, Cephalonia; Turkey-Constantinople, Smyrna; Palestine-Jerusalem; Africa-Tunis, Algiers, Alexandria, Suakin, Massowah, Zanzibar, Kimberley (?), Aden; India-Calcutta, Mian-Mir, Nowshera, Secunderabad, Simla, Delhi, Lucknow, Agra, Allahabad, Choabattia, Subatha, Assam, Swat Valley; China-Hongkong; Philippine Islands; Fiji Islands; North America-Mississippi Valley (?); West Indies (?)—Cuba (?), Porto Rico (?); South America-Venezuela, Brazil, Montevideo.

Malta fever is a general infection not unlike other specific bacteremias, such as typhoid fever. The Micrococcus melitensis is found. especially in the spleen and also in the blood. The inoculation of pure cultures of this organism into monkeys produces a prolonged febrile disease similar to Malta fever. There have been several instances of the inoculation of pure cultures into man, both intentionally and accidentally, which were followed by the characteristic symptoms of the fever after an incubation period of from five to fifteen days. Little doubt, therefore, remains that the organism is the true cause of the disease.

From the standpoint of prophylaxis it is of the first importance. to determine the channel of infection by which the micrococcus enters the body. In the cases before mentioned in which the disease was produced by inoculating pure cultures of the Micrococcus melitensis into man, in one instance the culture was accidentally introduced into the conjunctival sac; in the others, by subcutaneous inoculation. One case which arose in England is supposed to have been conveyed from son to father by using a clinical thermometer in the mouth immediately after its use by the patient. From experimental evidence, therefore, it would appear that the infection of Malta fever may be taken in through wounds, the mucous membranes, or by food and drink introduced into the mouth. There is no evidence that the disease is directly contagious from the sick to the well.

Malta fever occurs especially in the officers and men of the British army and navy stationed at Malta and Gibraltar. All authorities recognize the influence of unfavorable hygienic conditions as an etiological factor of the greatest importance in prophylaxis. Sex has no predisposing influence and every age is prone to attacks, but it occurs mostly between the ages of 6 and 30 years.

In Malta the greatest incidence of the disease is in the hot, dry month of July. Chilling of the surface, bodily and mental depression, etc., are quoted as incidental causes.

The morbid process is that of a general infection and is seen especially in the condition of the spleen, which is enlarged, soft, even

diffluent. The blood gives the usual picture of secondary anemia. The lymphoid elements are but slightly involved; the liver is congested and the seat of cloudy swelling, and the kidneys are sometimes swollen and show glomerular nephritis.

The period of incubation appears to be from a few days to thirty days, usually about fifteen.

On account of the large number of cases of Malta fever in the military and naval population of the island of Malta a commission was appointed by the admiralty, the war office, and the civil government of Malta in 1904 for the purpose of studying this disease with a view especially of determining the source of infection. This commission up to the present time has issued six reports. These reports include a minute study of the general sanitary conditions of the island of Malta, the prevalence of the disease there, the various experiments upon the viability of the organism under many conditions, and experimental work upon susceptible animals. The following data in regard to the relation of goat's milk to the spread of Malta fever are largely drawn from these reports and, in many instances, are taken verbatim from the reports.

Until the researches of the commission the means of infection were not definitely known. Various theories had been suggested, such as the agency of biting insects, the ingestion of infected food and drink, the breathing of infected dust, and contacts.

Epidemiological studies having shown that, while the consumption of infected milk may and probably does account for Malta fever among the Maltese, yet many cases occur among the military and naval population in Malta which can not be attributed to this cause. Accordingly a study of mosquitoes as possible carriers of the M. melitensis was begun.

The M. melitensis was recovered four times from a total of 896 mosquitoes dissected. Deducting from these 896 mosquitoes those collected where there was no case of Malta fever or where the cases were mostly chronic we would have 4 infected mosquitoes out of 450 collected in presumably infected places. This result was not unexpected considering the small numbers of the specific organisms found in the peripheral blood of Malta fever patients. The mosquitoes could not be infected in great numbers or the disease would be much more prevalent than it is at present.

a

Captain Kennedy was able experimentally to infect a monkey as the result of bites of mosquitoes (Culex pipiens) which had fed on patients suffering from Malta fever. An attempt to infect a monkey by bites from artificially infected mosquitoes, however, failed.

"Reports of the commission

fever

*

* for the investigation of Mediterranean

*. Part 4, 1906, p. 187..

In the examination of 103 cases of Malta fever for the specific organism the minimum quantity of blood from which a positive result was obtained was cubic centimeters. This fact has an important bearing on the question of the possibility of the transmission of infection by biting insects such as mosquitoes. This is a larger amount of blood than any biting insect to be found in Malta. can contain."

The water supply of Malta is drawn from two sources, the one for general use being derived from three springs which are pumped to a central reservoir and thence distributed, the second being rain water, most of the houses being provided with cisterns for the collection of rain water which is largely used for drinking purposes.

The milk supply of Malta is derived almost entirely from goats, though there is a small number of cows on the island and condensed milk is used to some extent. The number of milk goats in Malta is probably at least 20,000.

As showing the prevalence of the disease in Malta the following figures are of interest: From 1894 to 1903 there was an average of 32 cases per 10,000 inhabitants per year in the civil population; for the same period in the military population the yearly average was 25.6 per 10,000; from 1901 to 1903, for which years only figures are obtainable, the yearly average was 28.55 per 10,000 among the naval population.

In regard to infection other than through goat's milk, Major Horrocks concludes that so far as the experiments go it appears that infection can not be conveyed from infected to healthy monkeys by skin contact alone, all other sources of infection being excluded. Infection can not be conveyed from infected to healthy monkeys by ecto-parasites alone. When healthy monkeys living in intimate contact with diseased monkeys, under mosquito-proof conditions, become infected, the infection is due to the absorption of the M. melitensis excreted in the urine of the diseased monkeys.

There is no evidence that Mediterranean fever can be contracted by contact with cutaneous surfaces uncontaminated by urine.

Infection can be acquired by the absorption of urine secreted by cases of Mediterranean fever, and this is probably one way in which workers in hospitals become infected.

There is evidence to show that monkeys can be infected by dry dust artificially contaminated with cultures of M. melitensis isolated from

the spleen of cases of Mediterranean fever. The path of absorption may be through the nares, throat, respiratory passages, and alimentary canal. Dry dust contaminated with the urine of cases of Mediterranean fever has given rise to infection in goats, but not in monkeys. The experience gained during the work performed in Malta during 1904-5 has convinced Horrocks that men are more susceptible than monkeys and goats. Shaw's work on ambulatory cases of Mediterranean fever among the Maltese has also shown that opportunities for the creation of infected dust are plentiful in Malta. Infected dry dust as a cause of Mediterranean fever can not therefore be discarded. When infection is acquired in this manner the incubation period is probably at least a month.

Mediterranean fever can be acquired by the absorption of infected goat's milk from the alimentary canal. The incubation period in this case is also probably long, and may even extend to two months. This mode of infection probably plays a great part in the causation of Mediterranean fever among the Maltese, who drink raw milk drawn at the doors of their houses.

Horrocks found that the M. melitensis could be recovered from khaki cotton, khaki serge, and blankets up to the eightieth day. Shaw recovered it from blue serge up to the seventy-eighth day.

The above results obtained by Horrocks upon the longevity of the organism upon khaki, cotton, etc., are important as showing the possible relation of fomites to the transmission of the disease.

The presence of ambulatory cases of Malta fever must be taken into account in the spread and continuance of the disease in Malta. These ambulatory cases constantly pass the specific organism in their urine and are undoubtedly as much a source of danger to those with whom they come in contact as are the bacillus carriers in typhoid fever.

The usual source of milk in Malta is the goat. These animals are driven about the streets and milked at the customer's door into his own container. The udders, which are abnormally large, often touch the ground and are very liable to be soiled. There are so many herds that it is often difficult for a householder to tell the source of his milk supply. No regulations are in force for the effectual control of these vendors.