Rapid Body Color Change Provides Lizards with Facultative Crypsis in the Eyes of Their Avian Predators.

AbstractColor change serves many antipredator functions and may allow animals to better match environments or disrupt outlines to prevent detection. Rapid color change could potentially provide camouflage to animals that frequently move among microhabitats. Determining the adaptiveness of whole-animal rapid color changes in natural habitats with respect to predator visual systems would greatly broaden our fundamental understanding of the evolution of rapid color change. We tested whether whole-body color change provides water anoles (Anolis aquaticus) with camouflage against avian predators and whether these rapid changes allow them to shift between environment matching and edge disruption. We manipulated A. aquaticus placement in natural microhabitats and used digital image analysis to quantify color matching, pattern matching, and edge disruption produced by microhabitat-induced color change. Color change reduced lizard detectability to predators in microhabitat-specific ways. Environment matching was favored when lizards were in solid-colored microhabitats, regardless of exposure to predators. Edge disruption was instead induced by high exposure and varied by body region. We provide the first evidence that rapid color change permits a tetrapod to flexibly employ the most optimal camouflaging strategy by form (e.g., color matching vs. edge disruption) to minimize detection in the eyes of its predators.

High household transmission of SARS-CoV-2 in the United States: living density, viral load, and disproportionate impact on communities of color

BackgroundFew prospective studies of SARS-CoV-2 transmission within households have been reported from the United States, where COVID-19 cases are the highest in the world and the pandemic has had disproportionate impact on communities of color. Methods and FindingsThis is a prospective observational study. Between April-October 2020, the UNC CO-HOST study enrolled 102 COVID-positive persons and 213 of their household members across the Piedmont region of North Carolina, including 45% who identified as Hispanic/Latinx or non-white. Households were enrolled a median of 6 days from onset of symptoms in the index case. Secondary cases within the household were detected either by PCR of a nasopharyngeal (NP) swab on study day 1 and weekly nasal swabs (days 7, 14, 21) thereafter, or based on seroconversion by day 28. After excluding household contacts exposed at the same time as the index case, the secondary attack rate (SAR) among susceptible household contacts was 60% (106/176, 95% CI 53%-67%). The majority of secondary cases were already infected at study enrollment (73/106), while 33 were observed during study follow-up. Despite the potential for continuous exposure and sequential transmission over time, 93% (84/90, 95% CI 86%-97%) of PCR-positive secondary cases were detected within 14 days of symptom onset in the index case, while 83% were detected within 10 days. Index cases with high NP viral load (>10^6 viral copies/ul) at enrollment were more likely to transmit virus to household contacts during the study (OR 4.9, 95% CI 1.3-18 p=0.02). Furthermore, NP viral load was correlated within families (ICC=0.44, 95% CI 0.26-0.60), meaning persons in the same household were more likely to have similar viral loads, suggesting an inoculum effect. High household living density was associated with a higher risk of secondary household transmission (OR 5.8, 95% CI 1.3-55) for households with >3 persons occupying <6 rooms (SAR=91%, 95% CI 71-98%). Index cases who self-identified as Hispanic/Latinx or non-white were more likely to experience a high living density and transmit virus to a household member, translating into an SAR in minority households of 70%, versus 52% in white households (p=0.05). ConclusionsSARS-CoV-2 transmits early and often among household members. Risk for spread and subsequent disease is elevated in high-inoculum households with limited living space. Very high infection rates due to household crowding likely contribute to the increased incidence of SARS-CoV-2 infection and morbidity observed among racial and ethnic minorities in the US. Quarantine for 14 days from symptom onset of the first case in the household is appropriate to prevent onward transmission from the household. Ultimately, primary prevention through equitable distribution of effective vaccines is of paramount importance. AUTHORS SUMMARYO_ST_ABSWhy was this study done?C_ST_ABSO_LIUnderstanding the secondary attack rate and the timing of transmission of SARS-CoV-2 within households is important to determine the role of household transmission in the larger pandemic and to guide public health policies about quarantine. C_LIO_LIProspective studies looking at the determinants of household transmission are sparse, particularly studies including substantial racial and ethnic minorities in the United States and studies with adequate follow-up to detect sequential transmission events. C_LIO_LIIdentifying individuals at high risk of transmitting and acquiring SARS-CoV-2 will inform strategies for reducing transmission in the household, or reducing disease in those exposed. C_LI What did the researchers do and find?O_LIBetween April-November 2020, the UNC CO-HOST study enrolled 102 households across the Piedmont region of North Carolina, including 45% with an index case who identified as racial or ethnic minorities. C_LIO_LIOverall secondary attack rate was 60% with two-thirds of cases already infected at study enrollment. C_LIO_LIDespite the potential for sequential transmission in the household, the majority of secondary cases were detected within 10 days of symptom onset of the index case. C_LIO_LIViral loads were correlated within families, suggesting an inoculum effect. C_LIO_LIHigh viral load in the index case was associated with a greater likelihood of household transmission. C_LIO_LISpouses/partners of the COVID-positive index case and household members with obesity were at higher risk of becoming infected. C_LIO_LIHigh household living density contributed to an increased risk of household transmission. C_LIO_LIRacial/ethnic minorities had an increased risk of acquiring SARS-CoV-2 in their households in comparison to members of the majority (white) racial group. C_LI What do these findings mean?O_LIHousehold transmission often occurs quickly after a household member is infected. C_LIO_LIHigh viral load increases the risk of transmission. C_LIO_LIHigh viral load cases cluster within households - suggesting high viral inoculum in the index case may put the whole household at risk for more severe disease. C_LIO_LIIncreased household density may promote transmission within racial and ethnic minority households. C_LIO_LIEarly at-home point-of-care testing, and ultimately vaccination, is necessary to effectively decrease household transmission. C_LI

Practical strategies for SARS-CoV-2 RT-PCR testing in resource-constrained settings

Alternatives to nasopharyngeal sampling are needed to increase capacity for SARS-CoV-2 testing. Among 275 participants, we piloted the collection of nasal mid-turbinate swabs amenable to self-testing, including polyester flocked swabs as well as 3D printed plastic lattice swabs, placed into viral transport media or an RNA stabilization agent. Flocked nasal swabs identified 104/121 individuals who were PCR-positive for SARS-CoV-2 by nasopharyngeal sampling (sensitivity 87%, 95% CI 79-92%), mostly missing those with low viral load (<103 viral copies/uL). 3D-printed nasal swabs showed similar sensitivity. When nasal swabs were placed directly into RNA preservative, the mean 1.4 log decrease in viral copies/uL compared to nasopharyngeal samples was reduced to <1 log, even when samples were left at room temperature for up to 7 days. We also evaluated pooling strategies that involved pooling specimens in the lab versus pooling swabs at the point of collection, finding both successfully detected samples >102 viral copies/uL.