Abstract. Experimental infection of non-human primates with simian malaria parasites offers a controlled system to study malarial immunity. Plasmodium cynomolgi (P. vivax-like) and P. knowlesi (P. falciparum-like) infections in the rhesus monkey were used as a model to test the hypothesis that initial acute infection stimulates type 1/pro-inflammatory cytokine expression followed by a gradual type 2/anti-inflammatory response upon re-infection. This study analyzed cytokine gene expression (interleukin-12, interferon-␥, tumor necrosis factor-␣ ס type 1; interleukin-4, interleukin-10 ס type 2) using a semi-quantitative reverse transcriptase−polymerase chain reaction in monkeys infected with each of the parasites (three per group). Clinicoparasitologic and serologic parameters were also monitored. Monkeys were reinfected to assess whether enhanced immunity could increase parasite clearance. The immune response to P. cynomolgi infection in rhesus monkeys seemed to be mediated by anti-parasite, pro-inflammatory responses during primary infection with a transition to protective type 2 responses after repeat infection. The immune responses to P. knowlesi infection were more varied. Anti-inflammatory responses were more prevalent during primary infection. Repeat infection stimulated a wide variety of responses; most included expression of tumor necrosis factor-␣, a cytokine that has been associated with inflammatory and host-destructive effects (weight loss, fever, anemia). These observations further confirmed that the simian malaria/rhesus monkey model is well suited for studies on the regulation of immunity to acute Plasmodium infection.
Studies of naturally-acquired immunity to malaria in endemic regions provide the potential for a greater understanding of the regulation of human immune responses to the malarial parasite. However, little is known about the acquisition of malaria-specific immunity in regions of unstable, meso-endemic or hypo-endemic transmission. Cytokine profiles - patterns in the expression of interleukin-4 (IL-4), interleukin-10, interleukin-12, interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha) - were therefore studied during the natural acquisition of immunity to Plasmodium falciparum and P. vivax among individuals from Buenaventura, a meso-endemic region on the Pacific Coast of Colombia. In general, specific type-1 immune responses, characterized by IFN-gamma expression, were more likely to develop during P. falciparum infection, whereas pro-inflammatory cytokine profiles (with TNF-alpha expression) were observed more frequently among the P. vivax infections. Type-2 cytokine profiles, characterized by dominant IL-4 expression, were infrequent. Expression of IL-4 probably occurs primarily after prolonged exposure to parasites (which would, by definition, not be common in a meso-endemic region).
Epidemiologic information about snakebites in Ecuador is scarce. Snakebites are more common in the lowlands east of the Andes, in the Amazon basin. In the present study, a retrospective review of all (n = 142) snakebite admissions to Hospital Pio XII, a regional health center/ hospital in the canton of Sucúa, Morona Santiago, Ecuador was carried out between the years of 1996 and 2000. Bites occurred more frequently during the months of March to May. The largest group of patients were in the 15to 49-year-old range (52.5%), and agricultural workers were the most affected of all patients by occupation (> 40%). In most cases of snakebite, patients could not identify the type of snake that had bitten them. A small number of patients (n = 60, 42.3%) received some type of treatment prior to arrival at the hospital. Bites occurred most frequently on the left lower extremity (31.7%). Typical symptoms included pain and local edema at the snakebite site; generalized symptoms such as fever, nausea, and vomiting were less frequent. Most patients (almost 90%) received antivenin during hospitalization in addition to supportive care. The mean hospital stay was 4.3 days. More than 90% of all 142 patients recovered, about 8% with local abscesses. Mortality was 2.9% and occurred as a result of complications, including renal failure, respiratory failure, and disseminated intravascular coagulation.
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