The American Journal of Tropical Medicine and Hygiene - Volume 54, Issue 1, 1996

The reservoir competence of two lizard species, the southeastern five-lined skink (Eumeces inexpectatus) and the green anole (Anolis carolinensis), for Borrelia burgdorferi was evaluated. Skinks and anoles were exposed by needle inoculation or tick bite to B. burgdorferi. Xenodiagnosis with larval Ixodes scapularis and culture of tissues were used to assess infection and the ability of infected lizards to infect attached ticks. Both lizard species were susceptible to B. burgdorferi by both routes of exposure. Xenodiagnostic ticks acquired spirochetes while feeding on both species. One tick that dropped from a skink on the ninth day after exposure was infected. The remainder of xenodiagnostic ticks that acquired spirochetes fed three weeks after exposure of the lizards to the spirochete. Lizards remained infectious to attached ticks for at least five weeks. Overall, more than 20% of xenodiagnostic larvae fed on southeastern five-lined skinks acquired spirochetes. Individual skinks infected up to 34% of attached ticks. A smaller proportion of ticks feeding on green anoles became infected. Borrelia burgdorferi recovered from infected lizards retained their infectivity for mammalian hosts. The ability of the lizards to sustain a Borrelia infection and infect attached ticks suggests that they may play a role in the maintenance of spirochete transmission.

This report describes one of the few remaining foci of endemic malaria on the island of Java, the Kokap subdistrict, near the southcentral coast. Kokap was hypoendemic in June 1994 with prevalence of parasitemia at 0.98% (n = 10,606 of 40,246 residents). Plasmodium vivax comprised 63% of infections and P. falciparum all others. The incidence of indigenous infection during 1993 was 48 cases/1,000 person-years (p-yr), and it was relatively uniform among age groups (38 to 53/1,000 p-yr). Nine deaths due to malaria had been recorded in the past three years (8.3 deaths per 100,000 p-yr); the case fatality rate was 0.17%. Subdistricts adjoining Kokap to the north, east, and south reported incidence rates of < 2 cases/1,000 p-yr. To the west, Purworejo District had a high case incidence (11 cases/1,000 p-yr) but other districts to the west did not (< 1.2 cases/1,000 p-yr). The highest case incidence village area within Kokap (169 cases/1,000 p-yr) bordered the district of Purworejo to the west. Endemic malaria in Kokap and Purworejo coincided with where steep hills and narrow valleys dominated the terrain.

When mosquitoes feed on a vertebrate host that is infected concurrently with virus and microfilariae (mf), both pathogens are ingested. If mf penetrate the mosquito midgut, a small portion of the ingested virus may disseminate directly into the mosquito hemocoel. This phenomenon, termed microfilarial enhancement of arboviral transmission, has the potential to enhance the infectivity of arboviruses to mosquitoes. We investigated whether concurrent ingestion of Brugia mf and eastern equine encephalitis virus would enhance the infectivity and subsequent transmissibility of the virus by Aedes mosquitoes. Trials with Ae. triseriatus and B. pahangi mf indicated that microfilarial enhancement was dose dependent. Both a sufficient number of penetrating mf and a sufficient viremia were required for enhancement to occur. Furthermore, studies with B. malayi and three species of Aedes indicated that under comparable conditions of host viremia and microfilaremia, microfilarial enhancement occurred in some mosquito species (i.e., Ae. aegypti and Ae. taeniorhynchus) but not in others (Ae. triseriatus). We suggest that certain key parameters determine whether dual virus/mf host infections will enhance arboviral infectivity to mosquitoes. These include species differences in the capacity of mf to penetrate the mosquito midgut, the amount of virus passing into the hemocoel during mf penetration, and the innate susceptibility of mosquitoes to hemocoelomically introduced virus.