Chesson strain Plasmodium vivax in Saimiri sciureus boliviensis monkeys

Nine Saimiri sciureus boliviensis monkeys were inoculated with sporozoites of Plasmodium vivax (Chesson strain) dissected from Anopheles stephensi mosquitoes infected by feeding on blood from infected chimpanzees. The animals were splenectomized 7 days after inoculation. Seven animals developed infections with prepatent periods ranging from 12 to 43 days (mean of 19.6 days). Parasitemias were low during the first 50 days. Maximum parasitemias in 5 animals in which the strain adapted ranged from 10,000 to 46,800 per mm3. Anopheles freeborni mosquitoes were infected by feeding on 4 of the monkeys.     

The Peruvian III strain of Plasmodium brasilianum in Saimiri sciureus boliviensis monkeys

A strain of Plasmodium brasilianum was isolated from a naturally infected Saimiri monkey from Peru and subsequently passaged to 21 splenectomized Saimiri sciureus boliviensis monkeys. Nine of 12 attempts to transmit infection by sporozoite inoculation were successful with prepatent periods ranging from 23 to 41 days. Gametocytes were infective to Anopheles freeborni, Anopheles stephensi, Anopheles dirus, Anopheles maculatus, and Anopheles gambiae mosquitoes. The strain demonstrated a high level of resistance to cure with chloroquine.     

Infection of Aotus and Saimiri monkeys with Plasmodium gonderi

Attempts were made to infect 4 species of New World monkeys (Saimiri boliviensis, Aotus nancymai, A. vociferans, A. azarae boliviensis) with Plasmodium gonderi, a malaria parasite of African monkeys. Sporozoites were obtained from Anopheles dirus or A. stephensi mosquitoes that fed on an infected rhesus monkey (Macaca mulatta). Inoculation of sporozoites was by injection of dissected sporozoites by either the intravenous or intrahepatic routes, or by mosquito bite. Liver biopsies done 7 or 8 days after sporozoite inoculation showed that hepatocytes of all 4 species of these New World monkeys supported exoerythrocytic stages of P. gonderi, but daily blood film examination during a 60-day observation period failed to detect blood stages of the parasite.     

Infection of Aotus azarae boliviensis monkeys with different strains of Plasmodium falciparum

Eleven strains of Plasmodium falciparum from Asia, Africa, and Central America were inoculated into a total of 58 splenectomized Aotus azarae boliviensis monkeys. Eight of the strains produced high-level parasitemias, whereas 3 (2 from Honduras and 1 from Zaire) produced only low-level parasitemias. Mosquito infections were only obtained during the first 2 linear passages of the Santa Lucia strain from El Salvador. The results indicate that this species of Aotus monkey is highly susceptible to infection with strains of P. falciparum from different geographic areas, and therefore may be useful for a number of chemotherapeutic or immunologic studies. Its usefulness for mosquito infection studies is very limited.     

Infection of Aotus azarae boliviensis monkeys with different strains of Plasmodium vivax

Sixty-seven splenectomized Aotus azarae boliviensis were infected with strains of Plasmodium vivax from Southeast Asia (2), New Guinea (2), North Korea (1), and Central America (3). Maximum parasitemias varied among the different strains, with the mean maximum parasitemia for the primary infection period being 16,200 per mm3. Animals previously infected with Plasmodium falciparum and Plasmodium malariae produced maximum parasitemias of 30,200 and 11,900 per mm3, respectively. Gametocytes infective to Anopheles freeborni mosquitoes were produced with 7 of the 8 strains examined.     

Sporozoite-induced infections of the Salvador I strain of Plasmodium vivax in Saimiri sciureus boliviensis monkeys

Twenty Saimiri sciureus boliviensis monkeys from Bolivia were inoculated intravenously with sporozoites of the Salvador I strain of Plasmodium vivax. All animals were splenectomized 7 days after inoculation. Inoculation of 100,000 sporozoites resulted in prepatent periods averaging 16.6 days; all monkeys developed high-level parasitemias with an average maximum of 103,000 per mm3. Inoculation of 10,000 sporozoites resulted in average prepatent periods of 19.4 days; one of the resulting infections produced a transient low-level parasitemia. Of 5 monkeys inoculated with 1,000 sporozoites, 4 had prepatent periods of from 24 to 35 days and 1 failed to demonstrate any parasitemia; 1 monkey supported a low-level transient parasitemia, whereas the other 3 monkeys had high-level parasitemias. It is proposed that by using a minimum inoculum of 10,000 sporozoites, the model system may be useful in the testing of anti-sporozoite vaccines directed against P. vivax.     

Age-related hormonal differences in cycling squirrel monkeys (Saimiri boliviensis boliviensis)

This study was planned to evaluate the poor reproductive performance of aged squirrel monkeys in a self-sustaining breeding colony. Two groups of monkeys aged 6–8 years (Group 1), and >12 years (Group 2) were evaluated. During the midbreeding season, daily blood samples were obtained for a period of 35 days from 10 animals in each group. Blood samples were assayed for serum estradiol (E), progesterone (P), and bioassayable luteinizing hormone (bio-LH) concentrations and the data were analyzed by ANOVA (analysis of variance). Bio-LH surges were less frequent in the aged breeders (Group 2). Total P output during periovulatory period (day ?;3 to day + 3) and the total P output during the luteal phases of the estrus cycles were significantly lower in aged squirrel monkeys (Group 2, P < 0.003). Although E peaks occurred less frequently in Group 2, they had higher concentrations as compared to Group 1 (P < 0.003). Cumulative periovulatory and luteal phase E levels did not differ between the two groups. The reduction in P output in aged squirrel monkeys may interfere with proper implantation, thus contributing to the lower pregnancy rate observed in this age group. The decreased frequency of bio-LH surges indicated less frequent ovulations in the aged animals which may further impair reproduction with aging. © 1994 Wiley-Liss, Inc.     

Transmission of the OS strain of Plasmodium inui to Saimiri sciureus boliviensis and Aotus azarae boliviensis monkeys by Anopheles dirus mosquitoes

Eight Saimiri and 7 Aotus monkeys were exposed to infection with the OS strain of Plasmodium inui via the bites of from 2 to 7 Anopheles dirus mosquitoes. All Saimiri monkeys developed high-level infections of from 152,000 to 500,000/mm3 after prepatent periods of from 14 to 17 days. Only 1 Aotus monkey developed a patent infection after a period of 28 days. Feeding on these animals failed to result in infection of An. dirus mosquitoes.     

Ovarian stimulation of squirrel monkeys (Saimiri boliviensis boliviensis) using pregnant mare serum gonadotropin

The application of assisted reproductive technologies (ART) to nonhuman primates has created opportunities for improving reproductive management in breeding colonies, and for creation of new animal models by genetic modification. One impediment to the application of ART in Saimiri spp. has been the lack of an effective gonadotropin preparation for ovarian stimulation. Pregnant mare serum gonadotropin (PMSG) is inexpensive and readily available, but its repeated use in rhesus monkeys has been associated with induction of a refractory state. We have compared PMSG to recombinant human follicle stimulating hormone (rhFSH) for controlled ovarian stimulation in Bolivian squirrel monkeys. Groups of mature squirrel monkeys received rhFSH (75 IU daily) or PMSG (250 IU twice daily) by subcutaneous injection for 4 d during the breeding season (November to January) or nonbreeding season (March to September). Serum estradiol (E2) was measured daily. Follicular growth was monitored by abdominal ultrasound. During the breeding season, PMSG induced a higher E2 response than did rhFSH, with mean E2 levels being significantly higher within 3 d of stimulation. Superior follicular development in PMSG animals was confirmed by abdominal ultrasonography. During the nonbreeding season, PMSG elicited a similar increase in serum E2 levels despite the fact that basal serum E2 is typically low during the nonbreeding season. Repeated use of PMSG (< or = 3 cycles of administration) produced no attenuation of the E2 response. We conclude that PMSG is highly effective for repeated cycles of controlled ovulation stimulation in the squirrel monkey.     

Microsatellite polymorphisms in Bolivian squirrel monkeys (Saimiri boliviensis)

Two different approaches were used to identify new microsatellite polymorphisms among captive Bolivian squirrel monkeys (Saimiri boliviensis). In the first case, PCR primers for published human microsatellite loci were screened using genomic DNA from squirrel monkeys. Six polymorphic loci were identified using DNA samples from 19 unrelated individuals. The average heterozygosity among these six loci is 0.73. In the second set of experiments, a DNA library was created from Saimiri genomic DNA, and clones were selected from that library by screening with probes containing di-, tri-, and tetranucleotide repeats. Six novel microsatellites were identified this way, with an average heterozygosity of 0.59. Primer pairs for these six cloned microsatellites were also screened using a series of DNA samples from ten other platyrrhine species to assess the potential utility of these loci in other taxa. This study provides 12 new DNA polymorphisms that will be useful for various studies of this genus and demonstrates that both approaches can be used to develop new DNA polymorphisms in platyrrhine species.     

Age-related diffuse chronic telogen effluvium- type alopecia in female squirrel monkeys (Saimiri boliviensis boliviensis)

We investigated the diffuse alopecia affecting some female squirrel monkeys (Saimiri boliviensis boliviensis) housed in a breeding facility. We randomly selected 100 female and 10 male animals and performed a complete physical exam and a hair assessment on all animals; blood tests, trichograms, hair density; and skin biopsies in representative cases; and a dominance behavioral assessment of 50 animals. Hair coat was normal in 35 female monkeys and all 10 male animals. Of the 65 females with diffuse alopecia, 17 had mild, 22 moderate, and 26 severe hair loss. The alopecia group had a mean age of 9.6 +/- 0.6 years, whereas that of the normal group was 4.7 +/- 0.6 years (P < 0.05). The parity in the alopecia group was 4.2 +/- 0.6 but 2.0 +/- 0.6 (P < 0.05) in the normal group. There were no statistically significant differences in body weight, hemoglobin, blood urea nitrogen, serum glucose, liver aspartate aminotransaminase, or free thyroxine. The trichogram demonstrated 20.8% +/- 1.6% (mean +/- standard error) of telogen hairs in the alopecia group compared with 9.5% +/- 2.8% of the control group (P < 0.05). The hair density in the alopecia group was 52.8 +/- 4.1/cm2 and 79.6 +/- 14.3/cm2 in the control group. Skin biopsies in affected monkeys demonstrated increased telogen follicles, with no fibrosis or inflammation. There were no statistically significant differences in the dominance behavioral analysis. The findings are consistent with chronic telogen effluvium (CTE). A number of organic, behavioral, and dominance-related stress causes of CTE were excluded. CTE appears to be predominantly age-related in this population. CTE in female squirrel monkeys may serve as an animal model for human diffuse alopecia.     

Transmission of Plasmodium fragile to Saimiri monkeys

Saimiri monkeys from Bolivia and Guyana were infected with the Nilgiri and Ceylon strains of Plasmodium fragile. Of 20 attempted sporozoite transmissions of the Ceylon strain involving 11 splenectomized Saimiri sciureus boliviensis, only 8 were successful, 2 by mosquito bite and 6 by intravenous injection of sporozoites dissected from salivary glands. Prepatent periods ranged from 18 to 30 days with a mean of 25.8 days.     

Captive breeding of squirrel monkeys,Saimiri sciureus and Saimiri boliviensis: The problem of hybrid groups

The electrophoretic variability of blood proteins coding for up to 32 genetic loci was analyzed in 108 squirrel monkeys (Saimiri sciureus, Saimiri boliviensis, hybrids) from two captive colonies. Twelve polymorphic loci with 31 alleles are reported. The biallelic Ada* locus, G-statistics and Hardy-Weinberg genotype equilibria are useful for recognizing hybrids between S. sciureus and S. boliviensis. Backcrosses in hybrid stocks and gene flow in a natural hybrid belt, however, complicate the taxonomic diagnosis of captive specimens: S. sciureus phenotypes imported from Peru possessed the allele Ada*132, which generally characterizes S. boliviensis (or species hybrids). The complex taxonomy of Saimiri spp. Requires careful planning of captive breeding. We suggest a genetic analysis of the founder individuals before their inclusion in the European studbook population and to breed S. sciureus from Guyana separately from Peruvian imports, because the latter bear a greater risk of being taxonomically heterogeneous. Zoo Biol 17:95–109, 1998. © 1998 Wiley-Liss, Inc.     

The Uganda I/CDC strain of Plasmodium malariae in Saimiri sciureus boliviensis

The Uganda I/CDC strain of Plasmodium malariae, initially adapted to monkeys of the genus Aotus, was studied in splenectomized Saimiri sciureus boliviensis. Mean maximum parasitemia ranged from 248 to 22,134/mm3. Only 1 mosquito was infected of 2,238 examined. After the parasite was adapted to this host, infections were characterized by periods of detectable parasitemia extending up to 269 days and by sustained periods when parasite counts were greater than 1,000/mm3. After 4 linear passages, the developmental time required before the primary peak parasite count was approximately 2 mo.     

Effects of 17-hydroxyprogesterone caproate (17-OHPC) administration to pregnant squirrel monkeys (Saimiri boliviensis boliviensis)

Poor reproductive performance of the squirrel monkey (Saimiri boliviensis boliviensis) in captivity and a relative progesterone (P) deficiency in pregnancy have been reported. Since premature births may contribute to pregnancy wastage, we attempted to measure the effectiveness of 17-hydroxyprogesterone caproate (17-OHPC) treatment of pregnant squirrel monkeys to prevent early deliveries. Based on clearance studies of nonpregnant animals, 25 mg of 17-OHPC was administered at 6-day intervals to a test group of 31 pregnant monkeys while the control group of 29 received saline. Venous blood was obtained at 6- to 12-day intervals for measurement of 17-hydroxyprogesterone (17-OHP), P, 17-B estradiol (E), and androstenedione (A), and dihydroepiandrosterone (DHEA) levels by radioimmunoassays. The treated group had a significant increase in serum 17-OHP (P < 0.001), P (P < 0.01), and DHEA (P < 0.05) levels compared to controls. The numbers of live births, stillbirths, or neonatal deaths did not differ significantly between groups. Although 17-OHPC administration appeared to increase P and 17-OHP levels, this did not alter the duration of pregnancy nor delay the onset of labor. A significant fall in 17-OHP, P, and E levels was observed 6–12 days before delivery.     

Male behavior through the breeding season in Saimiri boliviensis boliviensis

The Bolivian squirrel monkey (Saimiri boliviensis boliviensis) is a seasonal breeder. Male squirrel monkeys show distinct morphological and behavioral changes prior to and during the breeding season. A “fatting syndrome” includes increased body weight, increased levels of androgens, and in the Bolivian subspecies, an increasingly active role in the social organization of the group. In this study, the behavior of ten adult male Bolivian squirrel monkeys was analyzed over a 6-month period prior to, during, and after the breeding season. Each was housed as the only adult male in a breeding unit with six to ten adult females and one juvenile male. Employing a principle components method, 11 behavioral clusters were generated from 27 responses. Their activity clusters were identified as follows: sexual activity that showed a peak around the time of peak conceptions; excitatory activity that was initially high but decreased throughout the breeding season; and maintenance activity that did not change across the breeding season. The changing social behavior of the male squirrel monkey parallels physiological changes and is correlated with changing androgen levels.     

Gait selection and the ontogeny of quadrupedal walking in squirrel monkeys (Saimiri boliviensis)

Locomotor researchers have long known that adult primates employ a unique footfall sequence during walking. Most mammals use lateral sequence (LS) gaits, in which hind foot touchdowns are followed by ipsilateral forefoot touchdowns. In contrast, most quadrupedal primates use diagonal sequence (DS) gaits, in which hind foot touchdowns are followed by contralateral forefoot touchdowns. However, gait selection in immature primates is more variable, with infants and juveniles frequently using LS gaits either exclusively or in addition to DS gaits. I explored the developmental bases for this phenomenon by examining the ontogeny of gait selection in juvenile squirrel monkeys walking on flat and simulated arboreal substrates (i.e., a raised pole). Although DS gaits predominated throughout development, the juvenile squirrel monkeys nonetheless utilized LS gaits in one-third of the ground strides and in one-sixth of pole strides. Multiple logistic regression analyses showed that gait selection within the juvenile squirrel monkey sample was not significantly associated with either age or body mass per se, arguing against the oft-cited argument that general neuromuscular maturation is responsible for ontogenetic changes in preferred footfall sequence. Rather, lower level biomechanical variables, specifically the position of the whole-body center of mass and the potential for interference between ipsilateral fore and hindlimbs, best explained variation in footfall patterns. Overall, results demonstrate the promise of developmental studies of growth and locomotor development to serve as "natural laboratories" in which to explore how variability in morphology is, or is not, associated with variability in locomotor behavior.