Brugia pahangi Infections in Mongolian Jirds and Dogs Following the Ocular Inoculation of Infective Larvae

Abstract

Infective larvae of Brugia pahangi collected from mosquitoes readily infected Mongolian jirds or dogs when placed on the intact eyeball. Histological studies in jirds showed that the larvae quickly penetrated into the orbital tissues. Further study in jirds showed that the larvae migrated rapidly via the veins or lymphatic vessels to the lungs, produced pulmonary ecchymotic hemorrhages within 5 min, and then accumulated in the pleural cavity where they induced a profuse pleural exudate. A considerable number of larvae persisted in the heart or pulmonary artery of jirds. Some of the larvae migrated to the cervical, iliolumbar, and renal lymphatics of jirds and a few larvae traveled to the peritoneal cavity. Thus, ocular inoculation of infective 3rd-stage larvae in jirds produced an infection predominantly of the heart, lungs, and pleural cavity. Third-stage larvae that had developed for 2 days in the peritoneal cavity of jirds were not infective for this host by ocular inoculation. Although inoculation of infective 3rd-stage larvae regularly induced patent infections in both jirds and dogs, the numbers of circulating microfilariae were low. Experimental infections of Brugia pahangi, a lymphatic-dwelling filaria, are usually achieved by the introduction of the infective thirdstage larvae by either the bite of infected mosquitoes or surgical methods such as syringe injection or inoculation onto artificial puncture wounds (Ewert and Singh, 1969). The subcutaneous route of larval inoculation by syringe is most commonly used for establishing infection. By this route, infections have been induced by injecting infective larvae in man (Buckley, 1958), lower primates, dogs, cats, and rodents (cf. reviews by Nelson, 1969; Ash and Riley, 1970). Successful infections were also produced in Mongolian jirds by intraperitoneal (McCall et al., 1973) and oral (Gwadz and Chernin, 1972) routes of infection. This paper presents evidence indicating that infective third-stage larvae of B. pahangi placed upon the corneal surface of the eye penetrate the conjunctival epithelium of jirds and dogs and subsequently produce patent infections Received for publication 29 May 1973. * Published as paper 1043, University of Georgia Institute of Comparative Medicine. This work was supported in part by the U. S.Japan Cooperative Medical Science Program, administered by the Geographic Medicine Branch, NIAID, Contract 69-92; Grant AI 09280 from NIAID, NIH; and in part by NIH-General Support Grant 3-R01-AM14901. t Department of Biology, Millersville State College, Millersville, Pa. $ Deceased. with microfilaremia. Observations on the migratory behavior and pathways of the early developing stages of the parasite are also presented. MATERIALS AND METHODS The animals used in this work were juvenile jirds (Meriones unguiculatus) procured from commercial sources and laboratory-reared mongrel dogs (Males, approximately 4 months old). Infective third-stage larvae of Brugia pahangi were obtained from Aedes aegypti (Liverpool strain) 10 days after the infective blood meals, by procedures previously described (Ah and Thompson, 1973). Inocula were prepared in Hanks' balanced salt solution (HBSS) by placing thoroughly washed infective larvae in 1-ml syringes. To permit prompt settling of larvae at the tip of the syringe barrel, the syringes containing the suspension were placed upright in the test tube rack. The larvae concentrated at the bottom of syringes were placed on the surface of the right eyeball of jirds by expelling a minute amount of HBSS. In dogs, drops of larval suspension were instilled onto the eyeball. Inoculations were done without anesthesia. Microfilarial counts were made by examining Giemsa-stained thick films of 20-mm3 samples of blood. At necropsy, all jirds were examined with the aid of a dissecting microscope. Generally, the protocol was as follows: (1) examination of all major lymphatic vessels and nodes, based upon prior studies of their location using Evans blue (Ah and Thompson, 1973); (2) examinations of heart blood, heart, lungs, and washings of pleural and peritoneal cavities; and (3) search of the subcutaneous tissues and removed skin, directly and by soaking. Recovery of the larvae from heart