Entomologic index for human risk of Lyme disease.

An entomologic index based on density estimates of Lyme disease spirochete-infected nymphal deer ticks (lxodes scapularis) was developed to assess human risk of Lyme disease. The authors used a standardized protocol to determine tick density and infection in numerous forested sites in six Rhode Island towns. An entomologic risk index calculated for each town was compared with the number of human Lyme disease cases reported to the Rhode Island State Health Department for the same year. A strong positive relation between entomologic risk index and the Lyme disease case rate for each town suggested that the entomologic index was predictive of Lyme disease risk.

Methods for evaluating Lyme disease risks using geographic information systems and geospatial analysis.

Lyme disease is a tick-transmitted borreliosis of humans and domestic animals emerging as one of the most significant threats to public health in north temperate regions of the world. However, despite a myriad of studies into symptomology, causes, and treatment of the disease, few researchers have addressed the spatial aspects of Lyme disease transmission. Using statewide data collected in Rhode Island (United States) as a test case, we demonstrated that exposure to deer ticks and the risk of contracting Lyme disease occurs mostly in the peridomestic environment. A Geographic Information System model was developed indicating a strong association among Lyme disease in humans, the degree of nymphal blacklegged tick, Ixodes scapularis Say, abundance in the environment, and prevalence of Borrelia burgdorferi infection in ticks. In contrast, occurrence of plant communities suitable for sustaining I. scapularis populations (forests) was not predictive of Lyme disease risk. Instead, we observed a highly significant spatial trend for decreasing number of ticks and incident cases of Lyme disease with increasing latitude. Geostatistics were employed for modeling spatial autocorrelation of tick densities. These findings were combined to create a model that predicts Lyme disease transmission risk, thereby demonstrating the utility of incorporating geospatial modeling techniques in studying the epidemiology of Lyme disease.

Entomological correlates of Babesia microti prevalence in an area where Ixodes scapularis (Acari:Ixodidae) is endemic.

Zoonotic prevalence of Babesia microti Franca piroplasms infecting white-footed mice, Peromyscus leucopus Rafinesque, was determined at 34 sites in Rhode Island where nymphal blacklegged tick, Ixodes scapularis Say, densities ranged from low to hyperabundant (1.7-525.3 nymphs per hour of flagging). Babesia was only detected at sites where tick abundance was moderate to high (> 20 nymphs per hour of flagging) and appeared to exhibit a clumped distribution. Where B. microti was detected, the mean number of nymphal ticks collected per hour of flagging was 229.2 compared with a mean of 40.1 at sites where Babesia was not detected. By combining the spatial occurrence of Babesia with a tick density database in a geographic information system, it may be possible to predict the pattern of zoonotic and human infection with B. microti.

Determining the duration of Ixodes scapularis (Acari: Ixodidae) attachment to tick-bite victims.

The duration of tick attachment is one factor associated with risk for human infection caused by several tick-borne pathogens. We measured tick engorgement indices at known time intervals after tick attachment and used these indices to determine the length of time that ticks were attached to tick-bite victims in selected Rhode Island and Pennsylvania communities where the agents of Lyme disease and human babesiosis occur. The total body length and width as well as the length and width of the scutum were measured on nymphal and adult female Ixodes scapularis Say removed from laboratory animals at 0, 12, 24, 36, 48, 60, and 72 h after their attachment. Three engorgement indices were calculated at each time interval. In addition, engorgement indices measurements were recorded for 504 ticks submitted to a commercial laboratory for pathogen detection testing between 1990 and 1992. No detectable change was observed in the average engorgement indices for either nymphal or adult ticks between 0 and 24 h of attachment using any of the engorgement indices. After 24 h of tick attachment, all engorgement indices continuously increased: average indices for nymphs attached 36, 48, and 60 h were significantly different from those attached < or = 24 h and from each other. Similarly, average engorgement indices for adult ticks attached < or = 36 h were significantly different from those attached for 48 h or more. More than 60% of tick-bite victims removed adult ticks by 36 h of attachment, but only 10% found and removed the smaller nymphal ticks within the first 24 h of tick feeding. The duration of tick attachment may serve as a useful predictor of risk for acquiring various infections, such as Lyme disease and babesiosis, transmitted by I. scapularis. Regression equations developed herein correlate tick engorgement indices with duration of feeding. A table containing specific engorgement index prediction intervals calculated for both nymphs and adults will allow the practitioner or clinical laboratory to use easily measured tick engorgement indices to predict transmission risk by determining the duration of feeding by individual ticks.

Visual hallucinations in patients with macular degeneration.

OBJECTIVE: This study was undertaken to determine the prevalence of visual hallucinations in patients with macular degeneration, describe such hallucinations phenomenologically, and possibly determine factors predisposing to their development. METHOD: Using a case-control design, the authors screened 100 consecutive patients with age-related macular degeneration for visual hallucinations. Each patient with visual hallucinations was matched to the next three patients without hallucinations. The patients and comparison subjects were compared in terms of scores on the Beck Depression Inventory, Eysenck Personality Questionnaire, Telephone Interview for Cognitive Status, and a structured questionnaire including demographic characteristics, family history, and medical and psychiatric history. Ophthalmologic data were obtained by chart review. RESULTS: Of the 100 patients, 13 experienced visual hallucinations. Four variables were significantly associated with having hallucinations: living alone, lower cognition score, history of stroke, and bilaterally worse visual acuity. Hallucinations were not associated with family or personal history of psychiatric disorder or with personality traits. In 11 (84.6%) of the 13 patients, the hallucinations had begun in association with an acute change in vision. CONCLUSION: These results indicate that visual hallucinations are prevalent among patients with macular degeneration. They appear unrelated to primary psychiatric disorder. The predisposing factors of bilaterally worse vision and living alone support an association with sensory deprivation, while history of stroke and worse cognition support a decreased cortical inhibition theory.