Tropical Diseases/Chapter 16

by Patrick Manson

CHAPTER XVI

PHLEBOTOMUS FEVER

Definition.— A specific fever of short duration and no mortality, caused by a germ— ultramicroscopic—introduced by the bite of the sand-fly (phlebotomus).

History.— This disease has been recognized clinically for upwards of a century and described under a variety of local names; but its definite relation to its transmitting agent, although suspected by McCarrison (if his three days' fever of Chitral be the same) in 1903 and by Taussig in 1905, was not established till 1908, when Doerr published his observations of the infectivity of the blood in this form of fever and the role of the sand-fly as transmitter. Doerr's conclusions have been confirmed by numerous observers in Malta and elsewhere around the Mediterranean, including Kilroy. Kilroy exposed himself for five nights to the bites of sand-flies on Suda Island, where these insects are particularly abundant and where phlebotomus fever is prevalent; subsequently, at the end of the first day of his fever, he injected his blood into a healthy man and thereby communicated the disease.

Geographical and seasonal distribution.— The range of phlebotomus fever is probably co-extensive with that of the insect transmitter. In the tropics it may break out at any time as an epidemic amongst new arrivals; in the sub-tropics it occurs only or principally during the summer and early autumn. Where the phlebotomus is absent, e.g.Bermuda (Birt), the fever is not found. In some phlebotomus-haunted places as many as 50 per cent, of new-comers are attacked.

Etiology.— The germ resides in the blood of the patient during the first day or two of the fever. It is ultramicroscopic, passing through filters which arrest Micrococcus melitensis. According to Doerr it is transmitted hereditarily through the egg and larva of phlebotomus to the imago; this, however, has not been firmly established experimentally.

Representatives of the genus Phlebotomus are to be found in most tropical and sub-tropical countries. The various species are usually designated "sand-flies." They are exceedingly minute, very delicate, yellowish, greyish, or brownish, somewhat slenderly built insects that bite principally during the night and

Fig. 62.—Female phlebotomus. (After Alcock.)

that can pass easily through the meshes of an ordinary mosquito net. At rest the wings are uplifted. The legs are long and slender; the wings, body and antennæ are thickly covered with short hairs. The joints of the antennæ are constricted. The proboscis is as long as the head. The tips of the piercing apparatus (which in other respects resembles that of the mosquito) project beyond the labium. The leaf-shaped wings are somewhat narrow and show all three branches of the second longitudinal vein very distinctly. (Fig. 62.)

P. papatasii (the species on which Doerr's observations were made, hence one of the names for the disease, papatasii fever) lays about forty eggs, selecting for the purpose damp localities such as the walls of cellars, of latrines, cesspools, crevices in walls, caves and embankments. The cycle of egg, larva and imago takes about one month in warm and upwards of two months in cooler weather to complete. The duration of the life of the imago is not known. It is difficult to keep it in captivity; under such conditions it rarely lives as long as fifteen days.^[1]

Fig. 63.—a, Abdomen of female phlebotomus, showing eggs; b, young phlebotomus. (After Alcock.)

There has been much confusion in the nomenclature of the various species of phlebotomus, and it has not been determined which of them, other than P. papatasii, convey the infection.

Pathology.—Yellow fever, dengue and phlebotomus fever have several important points in common, a circumstance suggestive of the possibility of a common or, at all events, a similar origin. Each is transmitted by an insect; their germs occur in the blood-stream and are ultramicroscopic; they are diseases of warm climates only; and, clinically, they are characterized by a short incubation period, a short and rapidly developed fever which is usually associated with relatively slow pulse and leucopenia, with relative decrease of the polynuclears. It would be interesting to ascertain if these diseases are mutually protective.

Symptoms.— These are practically the same as those described by McCarrison for the three-days' fever of Chitral, now regarded, as suggested by that observer, as being caused possibly by the sand-fly. After an incubation period of from one to six days, with or without a prodromal stage, the fever is ushered in by slight or more severe rigor. The face becomes flushed, headache is intense, and there is usually severe general aching. In from twenty-four to thirty-six hours the temperature has reached 103-4° F. It keeps about this point for a day longer, and then begins to fall, with or without epistaxis, vomiting, sweating, or diarrhœa, reaching the normal about the end of the third or beginning of the fourth day. The patient continues debilitated, especially mentally, for a week or two longer.

Serious complications do not occur, but in some years diarrhœa, in other years pharyngitis, are features of the epidemic.

There are no important sequelæ. Desquamation is very rare; a point which, together with the absence of an eruption, serves to differentiate this fever from dengue, a disease resembling it in many respects. The mortality is nil in the healthy.

Treatment.— There is no specific known for this disease. Treatment must therefore be conducted on general principles.

As it would appear that three-days' fever is a disease of locality, houses and places believed to be infected should be avoided, and, where possible, disinfected.

With a view to diminishing the local sand- fly pest, all rubbish should be burned or otherwise got rid of, ruinous walls should be demolished, latrines smoked with sulphur fumes and put into sanitary condition, dark damp places dried, whitewashed, and ventilated. By these and similar measures much can be done to control the infection. Unfortunately, a mosquito-net having a mesh sufficiently small to keep out sand-flies is intolerable to a white man in a hot climate, and the influence of the essential oils is too evanescent to be of practical value.

CHARACTERS OF THE GENUS PHLEBOTOMUS

Small hairy flies from 1.5-2.5 mm. in length, easily recognized by their form and thick hairy coat. The females only suck blood; in some people the bite causes a considerable local disturbance, in others little or none.

The greater part of the body is covered with long yellow hairs, for the most part, probably, modified scales. The antennæ have sixteen joints. The proboscis is as long as the head and contains a number of piercing organs.

The wings are definitely pointed, and on removal of the outer coating of scales the venation can be seen. The insect possesses six slender legs. The abdomen is divided into ten segments.

In the female the abdomen is spindle-shaped, and is provided with an upper and a lower pair of small claspers. In the male there are five pairs of sexual appendages— the upper and lower claspers, and various other structures known as the " submedian lamellæ," "intermediate appendages," and "intromittent organ" (Newstead).

The female lays her eggs in rubble walls and in caves. The eggs, six to nine days after being laid, hatch into twelve segmented caterpillar-like larvæ (Fig. 63), further characterized by two pairs of bristles on the posterior extremity and by the absence of eyes or organs of locomotion. In six to eight weeks the larvæ are 5 mm. in length, and feed on organic detritus and algæ. The pupæ are fixed in crevices of stones, slates, etc., the imagines emerging after fourteen days (Marett).

In the classification of these insects, entomologists have relied on the slender differences afforded by the venation of the wings, the length of segments of the palps, the number and arrangement of the bristles or spines on the claspers. Up to the present there has been little agreement on this subject. A synoptical table of the genus follows; but it should be remembered that this classification must be regarded as temporary until the group has been more extensively studied.

Great care must be exercised in the preservation of specimens for identification. The insects should be placed in a web-like layer of teased cotton-wool, but must not be covered with the wool, as even such slight pressure breaks their appendages.

SYNOPSIS OF THE GENUS

Asiatic and American Species
Marginal cell

Length of 2nd marginal cell 1/3 length of wing.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	(Head and abdomen brown; sides of thorax coxæ, and trochanters yellowish; legs, antennæ, and palpi grey; wings blue iridescence. P. argentipes (India).
Length of 2nd marginal cell more than 1/3 length of wing.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Grey, wings bluish iridescence. Greatest breadth of wing not quite 1/3 its length. P. major (India)
Length of 2nd marginal cell nearly 1/2 length of wing. Four spines on appendages of ♂.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Thorax, abdomen, and legs brown; wings purplish. Greatest breadth of wing 1/2 its length. P. malabaricus (India).
Length of 2nd marginal cell less than 1/4 length of wing.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Grey. Greatest breadth of wing between 1/4 and 1/5 its length. P. babu (India).
Length of 2nd marginal cell more than 1/3 length of wing. Superior appendages of ♂ bear three spines.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Yellowish-grey. Greatest breadth of wing slightly over 1/3 its length. P. himalayensis (India).
Length of 2nd marginal cell a little more than 1/4 length of wing.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Head and thorax yellowish-brown. Greatest breadth of wing 1/3 its length. P. perturbans (Java).
Length of 2nd marginal cell barely 1/3 length of wing.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Wings long and narrow. P. angustipennis (Java).
Length of 2nd marginal cell twice length of its petiole.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Yellow; mesonotum brown. P. vexator (N. America).
Length of 2nd marginal cell thrice length of its petiole.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Hairs chiefly yellow, otherwise like P. vexator P. cruciatus (Guatemala).
European Species Terminal segment of upper clasper
Terminal segment of upper clasper of ♂ slightly longer than lower segment.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Pale yellowish-grey; thorax dull red-brown with a median stripe. 2nd segment of palpi a little longer than 3rd. P. papatasii (Europe, Asia and Africa).
Terminal segment of upper clasper of ♂ slightly longer than lower segment.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Resembles P. papatasii, distinguished by darker integument and by shorter 6th longitudinal vein. P. nigerrimus (Europe).
Five spines of terminal segment of upper clasper very long and falciform, otherwise resembles P. papatasii.	$\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,}$	P. mascittii (Italy).
Terminal segment of upper clasper of ♂ half the length of the lower clasper.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	Abdominal hairs more or less erect. 2nd and 3rd segments of palpi equal in length. P. perniciosus (Malta and Asia).
Terminal segment of upper clasper of ♂ with only four spine.	$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$	2nd segment of palp half the length of the 3rd. Length of ♀ 2 mm P. minutus (Europe, Asia, and Africa)

Additional species have lately been described—P. rostrans (S. America) distinguished by the large size of its head, P. marginatus zeylanicus (Ceylon), P. antennatus (Gold Coast), P. squamipleuris (Khartoum), P. dubosqii (Africa), P. squamiventris and longipalpis (Brazil). It must be distinctly understood that this list is by no means final.

1. Lately, Wenyon has succeeded in keeping these insects alive as long as fifty days.