Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 28, No. 5, May 2022 1055 RESEARCH LETTERS The Vanuatu Health Program is supported by the Australian Department of Foreign Affairs and Trade Australian Aid Program. C.v.G. is a recipient of an Early Career Research Fellowship, supported by the Australian National Health and Medical Research Council. About the Author Dr. van Gemert is an epidemiologist and postdoctoral research fellow in the Vanuatu Health Program, Port Vila, Vanuatu, and with the Burnet Institute, Melbourne, Victoria, Australia. Her primary research interest is surveillance of infectious disease in resource-poor settings. References 1. Vanuatu Government Office of the President. Extraordinary Gazette Numbero Special No. 3. Extension of Declaration of State of Emergency Order No. 93 of 2020 [cited 2020 Jul 13]. https://www.gov.vu/index.php/events/news/86-exten- sion-of-the-declaration-of-the-soe-order-no-93-of-2020 2. Vanuatu Ministry of Health. Vanuatu situation report 59—23 December 2021 [cited 2022 Jan 10]. https://covid19.gov.vu/ images/Situation-reports/19122021_Vanuatu_COVID19_ NHEOC_SitRep_59_2.pdf 3. Yang B, Tsang TK, Wong JY, He Y, Gao H, Ho F, et al. The differential importation risks of COVID-19 from inbound travellers and the feasibility of targeted travel controls: a case study in Hong Kong. Lancet Reg Health West Pac. 2021;13:100184. https://doi.org/10.1016/j.lanwpc. 2021.100184 4. Clifford S, Pearson CA, Klepac P, Van Zandvoort K, Quilty BJ, Eggo RM, et al.; CMMID COVID-19 working group. Effectiveness of interventions targeting air travellers for delaying local outbreaks of SARS-CoV-2. J Travel Med. 2020;27:taaa068. https://doi.org/10.1093/ jtm/taaa068 5. World Health Organization. WHO coronavirus (COVID-19) dashboard 2022 [cited 2022 Jan 10]. https://covid19.who.int/ 6. Vanuatu National Statistics Office. Statistics update: international visitor arrivals. December 2020 provisional highlights [cited 2021 Feb 10]. https://www.stats.govt.nz/ information-releases/international-travel-december-2021 7. Pritchard E, Matthews PC, Stoesser N, Eyre DW, Gethings O, Vihta KD, et al. Impact of vaccination on new SARS-CoV-2 infections in the United Kingdom. Nat Med. 2021;27:1370–8. https://doi.org/10.1038/ s41591-021-01410-w Address for correspondence: Caroline van Gemert, The Burnet Institute, 85 Commercial Rd, Melbourne, VIC 3004, Australia; email: caroline.vangemert@burnet.edu.au SARS-CoV-2 Seroprevalence after Third Wave of Infections, South Africa Jackie Kleynhans, Stefano Tempia, Nicole Wolter, Anne von Gottberg, Jinal N. Bhiman, Amelia Buys, Jocelyn Moyes, Meredith L. McMorrow, Kathleen Kahn, F. Xavier Gómez-Olivé, Stephen Tollman, Neil A. Martinson, Floidy Wafawanaka, Limakatso Lebina, Jacques D. du Toit, Waasila Jassat, Mzimasi Neti, Marieke Brauer, Cheryl Cohen, for the PHIRST-C Group1 Author affiliations: National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa (J. Kleynhans, S. Tempia, N. Wolter, A. von Gottberg, J.N. Bhiman, A. Buys, J. Moyes, W. Jassat, M. Neti, C. Cohen); University of the Witwatersrand, Johannesburg (J. Kleynhans, S. Tempia, N. Wolter, A. von Gottberg, J.N. Bhiman, J. Moyes, C. Cohen); US Centers for Disease Control and Prevention, Atlanta, Georgia, USA (S. Tempia, M.L. McMorrow); US Centers for Disease Control and Prevention, Pretoria, South Africa (M.L. McMorrow); MRC/Wits Rural Public Health and Health Transitions Research Unit (Agincourt), University of the Witwatersrand, Johannesburg (K. Kahn, F.X. Gómez-Olivé, S. Tollman, F. Wafawanaka, J. du Toit); Johns Hopkins University Center for Tuberculosis Research, Baltimore, Maryland, USA (N.A. Martinson); Perinatal HIV Research Unit, University of the Witwatersrand, Johannesburg (N.A. Martinson, L. Lebina); Africa Health Research Institute, Durban, South Africa (L. Lebina); Ampath Pathology, Pretoria (M. Brauer) DOI: https://doi.org/10.3201/eid2805.220278 South Africa has experienced 4 waves of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections, the fourth dominated by the Omicron vari- ant of concern (1). Data on the proportion of the pop- ulation with serologic evidence of previous infection at the time of Omicron emergence are important to contextualize the observed rapid increases and subse- quent quick decline in case numbers (1), as well as the lower severity compared with previous variants (2). By November 2021, after the third wave of severe acute respiratory syndrome coronavirus 2 infections in South Af- rica, seroprevalence was 60% in a rural community and 70% in an urban community. High seroprevalence before the Omicron variant emerged may have contributed to re- duced illness severity observed in the fourth wave. 1Additional members of the PHIRST-C group who contributed to this article are listed at the end of this article. 1056 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 28, No. 5, May 2022 RESEARCH LETTERS We previously described the seroprevalence of SARS-CoV-2 in the PHIRST-C (Prospective House- hold Study of SARSCoV-2, Influenza, and Respira- tory Syncytial Virus Community Burden, Trans- mission Dynamics, and Viral Interaction) cohort in a rural and an urban community at 5 timepoints during July 2020–March 2021 (3). By using the same methods (Appendix, https://wwwnc.cdc.gov/ EID/article/28/5/22-0278-App1.pdf), we report seroprevalence at 4 additional timepoints through November 27, 2021, spanning the third, Delta-dom- inated wave (Appendix Figure 1), ending the week Omicron was identified (4). We tested serum sam- ples by using the Roche Elecsys Anti-SARS-CoV-2 assay (Roche Diagnostics, https://www.roche. com); we considered a cutoff index >1.0 an indica- tion of prior infection. The immunoassay detects nucleocapsid (N) antibodies; thus, it does not detect postvaccination antibody responses. We obtained se- roprevalence 95% credible intervals (CrIs) by using Bayesian inference with 10,000 posterior draws (5). We estimated the age- and sex-adjusted number of infections and age-adjusted diagnosed cases, hospi- talizations, deaths, case-to-infection ratio (CIR), hos- pitalization-to-infection ratio (HIR), and in-hospital and excess death fatality-to-infection ratio (FIR), as described previously (3) (Appendix). Third-wave infections were defined as participants who had a paired blood draw (BD) from the fifth timepoint of the previous study (BD5) (collected March 22–April 11, 2021) and from the ninth timepoint of this study (BD9) (collected November 15–27, 2021) and who were seronegative at BD5 and seropositive at BD9 or seropositive at BD5 but had a >2-fold higher cut- off index in BD9 (because 38 possible reinfections occurred after BD5 [Appendix]). We obtained vac- cination status through reviewing vaccine cards that participants kept at home. The study was approved by the University of the Witwatersrand Human Re- search Ethics Committee (reference no. 150808); the US Centers for Disease Control and Prevention re- lied on local clearance (IRB approval no. 6840). Overall, pre–third wave (BD5) SARS-CoV-2 sero- prevalence adjusted for assay sensitivity and speci- ficity was 26% (95% CrI 22%–29%) in the rural and 41% (95% CrI 37%–45%) in the urban community. After the third wave (BD9), overall seroprevalence increased to 60% (95% CrI 56%–64%) in the rural community and 70% (95% CrI 66%–74%) in the ur- ban community (Figure; Appendix Table 1). In both communities, the largest increase in seroprevalence was seen in children 13–18 years of age, who also had the highest seroprevalence of all ages after the third wave: 80% (95% CrI 70%–88%) in the rural commu- nity (a 49% increase) and 83% (95% CrI 73%–90%) in the urban community (a 19% increase). Figure. Severe acute respiratory syndrome coronavirus 2 seroprevalence at each blood collection, by age group, in a rural community (A) and urban community (B), South Africa, March 2020– November 2021. Baseline blood draw (BD1) collected July 20–September 17, 2020; second draw (BD2), September 21 – October 10, 2020; third draw (BD3), November 23– December 12, 2020; fourth draw (BD4), January 25– February 20, 2021; fifth draw (BD5), March 22–April 11, 2021; sixth draw (BD6), May 20–June 9, 2021; seventh draw (BD7), July 19–August 5, 2021; eighth draw (BD8), September 13–25, 2021; ninth draw (BD9), November 15–27, 2021. Error bars represent 95% credible intervals. Seroprevalence estimates adjusted for sensitivity and specificity of assay. Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 28, No. 5, May 2022 1057 RESEARCH LETTERS During the third wave of infections, the incidence at the rural site was 39% (95% CrI 24%–55%), result- ing in a CIR of 3% (95% CI 2%–5%). HIR was 0.5% (95% CI 0.3%–0.7%) and in-hospital FIR was 0.1% (95% CI 0.1%–0.2%); excess deaths FIR was 0.5% (95% CI 0.4%–0.8%) (Figure; Appendix Figure 2). In the urban community, the incidence during the third wave was 40% (95% CrI 26%–54%). CIR was a 5% (95% CI 4%–8%), and HIR was 2% (95% CI 2%– 4%). In-hospital FIR was 0.4% (95% CI 0.3%–0.6%) and excess deaths FIR was 0.6% (95% CI 0.4%–0.9%) (Figure; Appendix Figure 2). HIR and FIR were similar between wave 2 and 3 (Appendix Figure 3). SARS-CoV-2 vaccines became available in South Africa in February 2021, after the second wave. By the end of wave 3, only 8% (49/609) of participants were fully vaccinated (1 dose of John- son & Johnson/Janssen or 2 doses of Pfizer-BioN- Tech) in the rural community and 19% (97/512) in the urban community (Appendix Table 2). Considering the overall low vaccination coverage in these commu- nities during the study period, the similar HIR and FIR in wave 2 and 3 were likely driven by a combina- tion of natural immunity and potentially a moderate effect attributable to vaccination. Taken together, by the end of November 2021, just before the emergence of Omicron, the combined proportion of persons who had serologic evidence of previous infection (at any timepoint), were fully vac- cinated, or both was 62% (389/631) at the rural com- munity and 72% (411/568) at the urban community (Appendix Table 3). After the third wave of infections in South Africa, we observed a >60% overall seroprevalence attribut- able to SARS-CoV-2 infection, ranging from 43% in ru- ral community children <5 years of age to 83% in urban community children 13–18 years of age (Figure). CIR, HIR, and FIRs were similar between the second and third waves. Similar to our data, results from a study in Gauteng Province found seroprevalence of 56%–80% attributable to natural infection before the emergence of Omicron (6). The high seroprevalence before Omi- cron emergence may have contributed to reduced ill- ness severity observed in the fourth wave (2). Additional members of the PHIRST-C Group who contributed: Kgaugelo Patricia Kgasago, Linda de Gouveia, Maimuna Carrim, Mignon du Plessis, Retshidisitswe Kotane, and Tumelo Moloantoa. Acknowledgments We thank all persons participating in the study and the field teams for their hard work and dedication to the study, the laboratory teams, the PHIRST-C scientific and safety committee, the national SARS-CoV-2 National Institute for Communicable Diseases (NICD) surveillance team, and NICD Information Technology. This work was supported by the NICD of the National Health Laboratory Service and the US Centers for Disease Control and Prevention (cooperative agreement no. 6U01IP001048-04-02 awarded to C.C.). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. C.C. received grant funds from US Centers for Disease Control and Prevention, Wellcome Trust, and South African Medical Research Council. N.W. and A.v.G. received grant funds from Sanofi and the Gates Foundation. The investigators welcome enquiries about possible collaborations and requests for access to the dataset. Data will be shared after approval of a proposal and with a signed data access agreement. Investigators interested in more details about this study, or in accessing these resources, should contact the corresponding author. About the Author Ms. Kleynhans is an epidemiologist in the Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases. Her primary research interests include the epidemiology of respiratory diseases like influenza and COVID-19, vaccine impact studies, and modelling of infectious disease transmission dynamics. References 1. National Institute for Communicable Diseases. COVID-19 weekly epidemiology brief week 3. 2022 Jan 26 [cited 2022 Jan 31]. https://www.nicd.ac.za/wp-content/ uploads/2022/01/COVID-19-Weekly-Epidemiology- Brief-week-3-2022.pdf 2. Wolter N, Jassat W, Walaza S, Welch R, Moultrie H, Groome M, et al. Early assessment of the clinical severity of the SARS-CoV-2 omicron variant in South Africa: a data linkage study. Lancet. 2022;399:437–46. https://doi.org/ 10.1016/S0140-6736(22)00017-4 3. Kleynhans J, Tempia S, Wolter N, von Gottberg A, Bhiman JN, Buys A, et al.; PHIRST-C Group. PHIRST-C Group. SARS-CoV-2 seroprevalence in a rural and urban household cohort during first and second waves of infections, South Africa, July 2020–March 2021. Emerg Infect Dis. 2021;27:3020–9. https://doi.org/10.3201/eid2712.211465 4. World Health Organization. Classification of Omicron (B.1.1.529): SARS-CoV-2 variant of concern. 2021 Nov 26 [cited 2022 Jan 5]. https://www.who.int/news/ item/26-11-2021-classification-of-omicron-(b.1.1.529)-sars- cov-2-variant-of-concern 5. Larremore DB, Fosdick BK, Bubar KM, Zhang S, Kissler SM, Metcalf CJE, et al. Estimating SARS-CoV-2 seroprevalence and epidemiological parameters with uncertainty from serological surveys. eLife. 2021;10:e64206. https://doi.org/ 10.7554/eLife.64206 1058 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 28, No. 5, May 2022 RESEARCH LETTERS 6. Madhi SA, Kwatra G, Myers JE, Jassat W, Dhar N, Mukendi CK, et al. Population immunity and Covid-19 severity with Omicron variant in South Africa. N Engl J Med. 2022;NEJMoa2119658. https://doi.org/10.1056/ NEJMoa2119658 Address for correspondence: Jackie Kleynhans, Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases of the National Health Laboratory Service, 1 Modderfontein Rd, Sandringham, 2192, Johannesburg, South Africa; email: jackiel@nicd.ac.za Angiostrongylus cantonensis in a Red Ruffed Lemur at a Zoo, Louisiana, USA Jessica Rizor, Ryan A. Yanez, Tuddow Thaiwong, Matti Kiupel Authors affiliation: Michigan State University Veterinary Diagnostic Laboratory, Lansing, Michigan, USA DOI: https://doi.org/10.3201/eid2805.212287 Angiostrongylus cantonensis is a parasitic metastron- gyloid nematode that has a neurotropic larval stage and is endemic throughout Southeast Asia and the Pacific Islands. The rat (Rattus spp.) is the main definitive host and a variety of gastropods serve as intermediate hosts. In rats, infections cause no brain damage and only some pulmonary disease in severe infections. However, in aberrant hosts, including hu- mans and nonhuman primates, larvae cause severe eosinophilic meningoencephalitis. Clinical signs are associated with migration of the larvae and the im- mune response to dead or dying nematodes (1). In 1987, A. cantonensis nematodes were detected in rats in New Orleans, Louisiana, USA (2); in 1995, a human case of eosinophilic meningitis was reported in North America in a child from New Orleans (3). A. can- tonensis nematodes have now become endemic in the southeastern United States, as evidenced by reports of infection in a child in Texas (4); a horse from Mississippi (5); captive Geoffroy’s tamarins (Saguinus geoffroyi) in Alabama (6); and several animals in Florida, including a white-handed gibbon (Hylobates lar), an orangutan (Pongo pygmaeus), a white-throated capuchin monkey (Cebus capucinus), a red ruffed lemur (Varecia rubra), and a nine-banded armadillo (Dasypus novemcinctus) (7,8). Ingestion of infected gastropods and paratenic hosts or unwashed contaminated vegetables are pro- posed routes of infection for aberrant hosts. The International Union for Conservation of Na- ture lists red ruffed lemurs (Varecia rubra) as critically endangered (9). In June 2021, a 9-year-old male red ruffed lemur from a zoo in Louisiana was humanely euthanized because of hind limb paresis and a right head tilt that worsened over an 8-day period. The le- mur was housed in a troop of 5 adult lemurs in an out- door exhibit. Various snail species are common in the enclosure, but no other lemurs were clinically affected. A necropsy performed at the Michigan State University Veterinary Diagnostic Laboratory (Lan- sing, Michigan, USA) identified no gross lesions. The laboratory formalin-fixed and processed the brain, the entire spinal cord, and all major organs for his- topathology. Histopathologic examination revealed multiple transverse and longitudinal sections of adult nematodes within the subarachnoid space and neu- ropil of the cerebellum and brainstem. Nematodes were ≈50–70 μm in diameter and had a 3–4-μm thick smooth, eosinophilic cuticle and prominent lateral cords. Adult nematodes had coelomyarian muscula- ture, and the pseudocoelom contained a reproductive tract and an intestinal tract lined by multinucleated cells with flocculent eosinophilic to brown material in the lumen (Figure). Nematodes were surrounded by hemorrhage and small numbers of eosinophils, neu- trophils, macrophages, and glial cells. Several cerebel- lar folia were effaced by invading nematodes, hemor- rhage, and inflammation. The cerebellar meninges were expanded by numerous eosinophils, fewer neutrophils, foamy macrophages, multinucleated gi- ant cells, and lymphocytes. A representative section of thoracic spinal cord contained an identical single adult nematode in the subdural space. Another adult nematode had regionally effaced the dorsal horn in a section of lumbar spinal cord. The affected spinal cord had regional rarefaction of both gray and white A red ruffed lemur (Varecia rubra) from a zoo in Louisiana, USA, was euthanized for worsening paresis. Brain and spinal cord histology identified eosinophilic meningoen- cephalomyelitis with intralesional adult Angiostrongylus sp. nematodes. PCR and sequencing confirmed A. can- tonensis infection, indicating this parasite constitutes an emerging zoonosis in the southeastern United States.